The smallest value that can be represented by this integer type.

Examples

assert_eq!(usize::MIN, 0);

The largest value that can be represented by this integer type (2⁶⁴ − 1 on 64-bit targets).

Examples

assert_eq!(usize::MAX, 18446744073709551615);

The size of this integer type in bits.

Examples

assert_eq!(usize::BITS, 64);

Returns the number of ones in the binary representation of self.

Examples

let n = 0b01001100usize;
assert_eq!(n.count_ones(), 3);

let max = usize::MAX;
assert_eq!(max.count_ones(), 64);

let zero = 0usize;
assert_eq!(zero.count_ones(), 0);

Returns the number of zeros in the binary representation of self.

Examples

let zero = 0usize;
assert_eq!(zero.count_zeros(), 64);

let max = usize::MAX;
assert_eq!(max.count_zeros(), 0);

Returns the number of leading zeros in the binary representation of self.

Depending on what you’re doing with the value, you might also be interested in the ilog2 function which returns a consistent number, even if the type widens.

Examples

let n = usize::MAX >> 2;
assert_eq!(n.leading_zeros(), 2);

let zero = 0usize;
assert_eq!(zero.leading_zeros(), 64);

let max = usize::MAX;
assert_eq!(max.leading_zeros(), 0);

Returns the number of trailing zeros in the binary representation of self.

Examples

let n = 0b0101000usize;
assert_eq!(n.trailing_zeros(), 3);

let zero = 0usize;
assert_eq!(zero.trailing_zeros(), 64);

let max = usize::MAX;
assert_eq!(max.trailing_zeros(), 0);

Returns the number of leading ones in the binary representation of self.

Examples

let n = !(usize::MAX >> 2);
assert_eq!(n.leading_ones(), 2);

let zero = 0usize;
assert_eq!(zero.leading_ones(), 0);

let max = usize::MAX;
assert_eq!(max.leading_ones(), 64);

Returns the number of trailing ones in the binary representation of self.

Examples

let n = 0b1010111usize;
assert_eq!(n.trailing_ones(), 3);

let zero = 0usize;
assert_eq!(zero.trailing_ones(), 0);

let max = usize::MAX;
assert_eq!(max.trailing_ones(), 64);

Returns the minimum number of bits required to represent self.

This method returns zero if self is zero.

Examples

#![feature(uint_bit_width)]

assert_eq!(0_usize.bit_width(), 0);
assert_eq!(0b111_usize.bit_width(), 3);
assert_eq!(0b1110_usize.bit_width(), 4);
assert_eq!(usize::MAX.bit_width(), 64);

Returns self with only the most significant bit set, or 0 if the input is 0.

Examples

#![feature(isolate_most_least_significant_one)]

let n: usize = 0b_01100100;

assert_eq!(n.isolate_highest_one(), 0b_01000000);
assert_eq!(0_usize.isolate_highest_one(), 0);

Returns self with only the least significant bit set, or 0 if the input is 0.

Examples

#![feature(isolate_most_least_significant_one)]

let n: usize = 0b_01100100;

assert_eq!(n.isolate_lowest_one(), 0b_00000100);
assert_eq!(0_usize.isolate_lowest_one(), 0);

Returns the index of the highest bit set to one in self, or None if self is 0.

Examples

#![feature(int_lowest_highest_one)]

assert_eq!(0b0_usize.highest_one(), None);
assert_eq!(0b1_usize.highest_one(), Some(0));
assert_eq!(0b1_0000_usize.highest_one(), Some(4));
assert_eq!(0b1_1111_usize.highest_one(), Some(4));

Returns the index of the lowest bit set to one in self, or None if self is 0.

Examples

#![feature(int_lowest_highest_one)]

assert_eq!(0b0_usize.lowest_one(), None);
assert_eq!(0b1_usize.lowest_one(), Some(0));
assert_eq!(0b1_0000_usize.lowest_one(), Some(4));
assert_eq!(0b1_1111_usize.lowest_one(), Some(0));

Returns the bit pattern of self reinterpreted as a signed integer of the same size.

This produces the same result as an as cast, but ensures that the bit-width remains the same.

Examples

let n = usize::MAX;

assert_eq!(n.cast_signed(), -1isize);

Shifts the bits to the left by a specified amount, n, wrapping the truncated bits to the end of the resulting integer.

rotate_left(n) is equivalent to applying rotate_left(1) a total of n times. In particular, a rotation by the number of bits in self returns the input value unchanged.

Please note this isn’t the same operation as the << shifting operator!

Examples

let n = 0xaa00000000006e1usize;
let m = 0x6e10aa;

assert_eq!(n.rotate_left(12), m);
assert_eq!(n.rotate_left(1024), n);

Shifts the bits to the right by a specified amount, n, wrapping the truncated bits to the beginning of the resulting integer.

rotate_right(n) is equivalent to applying rotate_right(1) a total of n times. In particular, a rotation by the number of bits in self returns the input value unchanged.

Please note this isn’t the same operation as the >> shifting operator!

Examples

let n = 0x6e10aausize;
let m = 0xaa00000000006e1;

assert_eq!(n.rotate_right(12), m);
assert_eq!(n.rotate_right(1024), n);

Performs a left funnel shift (concatenates self with rhs, with self making up the most significant half, then shifts the combined value left by n, and most significant half is extracted to produce the result).

Please note this isn’t the same operation as the << shifting operator or rotate_left, although a.funnel_shl(a, n) is equivalent to a.rotate_left(n).

Panics

If n is greater than or equal to the number of bits in self

Examples

Basic usage:

#![feature(funnel_shifts)]
let a = 0xaa00000000006e1usize;
let b = 0x2fe78e45983acd98usize;
let m = 0x6e12fe;

assert_eq!(a.funnel_shl(b, 12), m);

Performs a right funnel shift (concatenates self and rhs, with self making up the most significant half, then shifts the combined value right by n, and least significant half is extracted to produce the result).

Please note this isn’t the same operation as the >> shifting operator or rotate_right, although a.funnel_shr(a, n) is equivalent to a.rotate_right(n).

Panics

If n is greater than or equal to the number of bits in self

Examples

Basic usage:

#![feature(funnel_shifts)]
let a = 0xaa00000000006e1usize;
let b = 0x2fe78e45983acd98usize;
let m = 0x6e12fe78e45983ac;

assert_eq!(a.funnel_shr(b, 12), m);

Reverses the byte order of the integer.

Examples

let n = 0x1234567890123456usize;
let m = n.swap_bytes();

assert_eq!(m, 0x5634129078563412);

Returns an integer with the bit locations specified by mask packed contiguously into the least significant bits of the result.

#![feature(uint_gather_scatter_bits)]
let n: usize = 0b1011_1100;

assert_eq!(n.gather_bits(0b0010_0100), 0b0000_0011);
assert_eq!(n.gather_bits(0xF0), 0b0000_1011);

Returns an integer with the least significant bits of self distributed to the bit locations specified by mask.

#![feature(uint_gather_scatter_bits)]
let n: usize = 0b1010_1101;

assert_eq!(n.scatter_bits(0b0101_0101), 0b0101_0001);
assert_eq!(n.scatter_bits(0xF0), 0b1101_0000);

Reverses the order of bits in the integer. The least significant bit becomes the most significant bit, second least-significant bit becomes second most-significant bit, etc.

Examples

let n = 0x1234567890123456usize;
let m = n.reverse_bits();

assert_eq!(m, 0x6a2c48091e6a2c48);
assert_eq!(0, 0usize.reverse_bits());

Converts an integer from big endian to the target’s endianness.

On big endian this is a no-op. On little endian the bytes are swapped.

Examples

let n = 0x1Ausize;

if cfg!(target_endian = "big") {
    assert_eq!(usize::from_be(n), n)
} else {
    assert_eq!(usize::from_be(n), n.swap_bytes())
}

Converts an integer from little endian to the target’s endianness.

On little endian this is a no-op. On big endian the bytes are swapped.

Examples

let n = 0x1Ausize;

if cfg!(target_endian = "little") {
    assert_eq!(usize::from_le(n), n)
} else {
    assert_eq!(usize::from_le(n), n.swap_bytes())
}

Converts self to big endian from the target’s endianness.

On big endian this is a no-op. On little endian the bytes are swapped.

Examples

let n = 0x1Ausize;

if cfg!(target_endian = "big") {
    assert_eq!(n.to_be(), n)
} else {
    assert_eq!(n.to_be(), n.swap_bytes())
}

Converts self to little endian from the target’s endianness.

On little endian this is a no-op. On big endian the bytes are swapped.

Examples

let n = 0x1Ausize;

if cfg!(target_endian = "little") {
    assert_eq!(n.to_le(), n)
} else {
    assert_eq!(n.to_le(), n.swap_bytes())
}

Checked integer addition. Computes self + rhs, returning None if overflow occurred.

Examples

assert_eq!((usize::MAX - 2).checked_add(1), Some(usize::MAX - 1));
assert_eq!((usize::MAX - 2).checked_add(3), None);

Strict integer addition. Computes self + rhs, panicking if overflow occurred.

Panics

Overflow behavior

This function will always panic on overflow, regardless of whether overflow checks are enabled.

Examples

assert_eq!((usize::MAX - 2).strict_add(1), usize::MAX - 1);

The following panics because of overflow:

let _ = (usize::MAX - 2).strict_add(3);

Unchecked integer addition. Computes self + rhs, assuming overflow cannot occur.

Calling x.unchecked_add(y) is semantically equivalent to calling x.checked_add(y).unwrap_unchecked().

If you’re just trying to avoid the panic in debug mode, then do not use this. Instead, you’re looking for wrapping_add.

Safety

This results in undefined behavior when self + rhs > usize::MAX or self + rhs < usize::MIN, i.e. when checked_add would return None.

Checked addition with a signed integer. Computes self + rhs, returning None if overflow occurred.

Examples

assert_eq!(1usize.checked_add_signed(2), Some(3));
assert_eq!(1usize.checked_add_signed(-2), None);
assert_eq!((usize::MAX - 2).checked_add_signed(3), None);

Strict addition with a signed integer. Computes self + rhs, panicking if overflow occurred.

Panics

Overflow behavior

This function will always panic on overflow, regardless of whether overflow checks are enabled.

Examples

assert_eq!(1usize.strict_add_signed(2), 3);

The following panic because of overflow:

let _ = 1usize.strict_add_signed(-2);

let _ = (usize::MAX - 2).strict_add_signed(3);

Checked integer subtraction. Computes self - rhs, returning None if overflow occurred.

Examples

assert_eq!(1usize.checked_sub(1), Some(0));
assert_eq!(0usize.checked_sub(1), None);

Strict integer subtraction. Computes self - rhs, panicking if overflow occurred.

Panics

Overflow behavior

This function will always panic on overflow, regardless of whether overflow checks are enabled.

Examples

assert_eq!(1usize.strict_sub(1), 0);

The following panics because of overflow:

let _ = 0usize.strict_sub(1);

Unchecked integer subtraction. Computes self - rhs, assuming overflow cannot occur.

Calling x.unchecked_sub(y) is semantically equivalent to calling x.checked_sub(y).unwrap_unchecked().

If you’re just trying to avoid the panic in debug mode, then do not use this. Instead, you’re looking for wrapping_sub.

If you find yourself writing code like this:

if foo >= bar {
    // SAFETY: just checked it will not overflow
    let diff = unsafe { foo.unchecked_sub(bar) };
    // ... use diff ...
}

Consider changing it to

if let Some(diff) = foo.checked_sub(bar) {
    // ... use diff ...
}

As that does exactly the same thing – including telling the optimizer that the subtraction cannot overflow – but avoids needing unsafe.

Safety

This results in undefined behavior when self - rhs > usize::MAX or self - rhs < usize::MIN, i.e. when checked_sub would return None.

Checked subtraction with a signed integer. Computes self - rhs, returning None if overflow occurred.

Examples

assert_eq!(1usize.checked_sub_signed(2), None);
assert_eq!(1usize.checked_sub_signed(-2), Some(3));
assert_eq!((usize::MAX - 2).checked_sub_signed(-4), None);

Strict subtraction with a signed integer. Computes self - rhs, panicking if overflow occurred.

Panics

Overflow behavior

This function will always panic on overflow, regardless of whether overflow checks are enabled.

Examples

assert_eq!(3usize.strict_sub_signed(2), 1);

The following panic because of overflow:

let _ = 1usize.strict_sub_signed(2);

let _ = (usize::MAX).strict_sub_signed(-1);

Checked integer subtraction. Computes self - rhs and checks if the result fits into an isize, returning None if overflow occurred.

Examples

assert_eq!(10usize.checked_signed_diff(2), Some(8));
assert_eq!(2usize.checked_signed_diff(10), Some(-8));
assert_eq!(usize::MAX.checked_signed_diff(isize::MAX as usize), None);
assert_eq!((isize::MAX as usize).checked_signed_diff(usize::MAX), Some(isize::MIN));
assert_eq!((isize::MAX as usize + 1).checked_signed_diff(0), None);
assert_eq!(usize::MAX.checked_signed_diff(usize::MAX), Some(0));

Checked integer multiplication. Computes self * rhs, returning None if overflow occurred.

Examples

assert_eq!(5usize.checked_mul(1), Some(5));
assert_eq!(usize::MAX.checked_mul(2), None);

Strict integer multiplication. Computes self * rhs, panicking if overflow occurred.

Panics

Overflow behavior

This function will always panic on overflow, regardless of whether overflow checks are enabled.

Examples

assert_eq!(5usize.strict_mul(1), 5);

The following panics because of overflow:

let _ = usize::MAX.strict_mul(2);

Unchecked integer multiplication. Computes self * rhs, assuming overflow cannot occur.

Calling x.unchecked_mul(y) is semantically equivalent to calling x.checked_mul(y).unwrap_unchecked().

If you’re just trying to avoid the panic in debug mode, then do not use this. Instead, you’re looking for wrapping_mul.

Safety

This results in undefined behavior when self * rhs > usize::MAX or self * rhs < usize::MIN, i.e. when checked_mul would return None.

Checked integer division. Computes self / rhs, returning None if rhs == 0.

Examples

assert_eq!(128usize.checked_div(2), Some(64));
assert_eq!(1usize.checked_div(0), None);

Strict integer division. Computes self / rhs.

Strict division on unsigned types is just normal division. There’s no way overflow could ever happen. This function exists so that all operations are accounted for in the strict operations.

Panics

This function will panic if rhs is zero.

Examples

assert_eq!(100usize.strict_div(10), 10);

The following panics because of division by zero:

let _ = (1usize).strict_div(0);

Checked Euclidean division. Computes self.div_euclid(rhs), returning None if rhs == 0.

Examples

assert_eq!(128usize.checked_div_euclid(2), Some(64));
assert_eq!(1usize.checked_div_euclid(0), None);

Strict Euclidean division. Computes self.div_euclid(rhs).

Strict division on unsigned types is just normal division. There’s no way overflow could ever happen. This function exists so that all operations are accounted for in the strict operations. Since, for the positive integers, all common definitions of division are equal, this is exactly equal to self.strict_div(rhs).

Panics

This function will panic if rhs is zero.

Examples

assert_eq!(100usize.strict_div_euclid(10), 10);

The following panics because of division by zero:

let _ = (1usize).strict_div_euclid(0);

Checked integer division without remainder. Computes self / rhs, returning None if rhs == 0 or if self % rhs != 0.

Examples

#![feature(exact_div)]
assert_eq!(64usize.checked_div_exact(2), Some(32));
assert_eq!(64usize.checked_div_exact(32), Some(2));
assert_eq!(64usize.checked_div_exact(0), None);
assert_eq!(65usize.checked_div_exact(2), None);

Integer division without remainder. Computes self / rhs, returning None if self % rhs != 0.

Panics

This function will panic if rhs == 0.

Examples

#![feature(exact_div)]
assert_eq!(64usize.div_exact(2), Some(32));
assert_eq!(64usize.div_exact(32), Some(2));
assert_eq!(65usize.div_exact(2), None);

Unchecked integer division without remainder. Computes self / rhs.

Safety

This results in undefined behavior when rhs == 0 or self % rhs != 0, i.e. when checked_div_exact would return None.

Checked integer remainder. Computes self % rhs, returning None if rhs == 0.

Examples

assert_eq!(5usize.checked_rem(2), Some(1));
assert_eq!(5usize.checked_rem(0), None);

Strict integer remainder. Computes self % rhs.

Strict remainder calculation on unsigned types is just the regular remainder calculation. There’s no way overflow could ever happen. This function exists so that all operations are accounted for in the strict operations.

Panics

This function will panic if rhs is zero.

Examples

assert_eq!(100usize.strict_rem(10), 0);

The following panics because of division by zero:

let _ = 5usize.strict_rem(0);

Checked Euclidean modulo. Computes self.rem_euclid(rhs), returning None if rhs == 0.

Examples

assert_eq!(5usize.checked_rem_euclid(2), Some(1));
assert_eq!(5usize.checked_rem_euclid(0), None);

Strict Euclidean modulo. Computes self.rem_euclid(rhs).

Strict modulo calculation on unsigned types is just the regular remainder calculation. There’s no way overflow could ever happen. This function exists so that all operations are accounted for in the strict operations. Since, for the positive integers, all common definitions of division are equal, this is exactly equal to self.strict_rem(rhs).

Panics

This function will panic if rhs is zero.

Examples

assert_eq!(100usize.strict_rem_euclid(10), 0);

The following panics because of division by zero:

let _ = 5usize.strict_rem_euclid(0);

Same value as self | other, but UB if any bit position is set in both inputs.

This is a situational micro-optimization for places where you’d rather use addition on some platforms and bitwise or on other platforms, based on exactly which instructions combine better with whatever else you’re doing. Note that there’s no reason to bother using this for places where it’s clear from the operations involved that they can’t overlap. For example, if you’re combining u16s into a u32 with ((a as u32) << 16) | (b as u32), that’s fine, as the backend will know those sides of the | are disjoint without needing help.

Examples

#![feature(disjoint_bitor)]

// SAFETY: `1` and `4` have no bits in common.
unsafe {
    assert_eq!(1_usize.unchecked_disjoint_bitor(4), 5);
}

Safety

Requires that (self & other) == 0, otherwise it’s immediate UB.

Equivalently, requires that (self | other) == (self + other).

Returns the logarithm of the number with respect to an arbitrary base, rounded down.

This method might not be optimized owing to implementation details; ilog2 can produce results more efficiently for base 2, and ilog10 can produce results more efficiently for base 10.

Panics

This function will panic if self is zero, or if base is less than 2.

Examples

assert_eq!(5usize.ilog(5), 1);

Returns the base 2 logarithm of the number, rounded down.

Panics

This function will panic if self is zero.

Examples

assert_eq!(2usize.ilog2(), 1);

Returns the base 10 logarithm of the number, rounded down.

Panics

This function will panic if self is zero.

Example

assert_eq!(10usize.ilog10(), 1);

Returns the logarithm of the number with respect to an arbitrary base, rounded down.

Returns None if the number is zero, or if the base is not at least 2.

This method might not be optimized owing to implementation details; checked_ilog2 can produce results more efficiently for base 2, and checked_ilog10 can produce results more efficiently for base 10.

Examples

assert_eq!(5usize.checked_ilog(5), Some(1));

Returns the base 2 logarithm of the number, rounded down.

Returns None if the number is zero.

Examples

assert_eq!(2usize.checked_ilog2(), Some(1));

Returns the base 10 logarithm of the number, rounded down.

Returns None if the number is zero.

Examples

assert_eq!(10usize.checked_ilog10(), Some(1));

Checked negation. Computes -self, returning None unless self == 0.

Note that negating any positive integer will overflow.

Examples

assert_eq!(0usize.checked_neg(), Some(0));
assert_eq!(1usize.checked_neg(), None);

Strict negation. Computes -self, panicking unless self == 0.

Note that negating any positive integer will overflow.

Panics

Overflow behavior

This function will always panic on overflow, regardless of whether overflow checks are enabled.

Examples

assert_eq!(0usize.strict_neg(), 0);

The following panics because of overflow:

let _ = 1usize.strict_neg();

Checked shift left. Computes self << rhs, returning None if rhs is larger than or equal to the number of bits in self.

Examples

assert_eq!(0x1usize.checked_shl(4), Some(0x10));
assert_eq!(0x10usize.checked_shl(129), None);
assert_eq!(0x10usize.checked_shl(63), Some(0));

Strict shift left. Computes self << rhs, panicking if rhs is larger than or equal to the number of bits in self.

Panics

Overflow behavior

This function will always panic on overflow, regardless of whether overflow checks are enabled.

Examples

assert_eq!(0x1usize.strict_shl(4), 0x10);

The following panics because of overflow:

let _ = 0x10usize.strict_shl(129);

Unchecked shift left. Computes self << rhs, assuming that rhs is less than the number of bits in self.

Safety

This results in undefined behavior if rhs is larger than or equal to the number of bits in self, i.e. when checked_shl would return None.

Unbounded shift left. Computes self << rhs, without bounding the value of rhs.

If rhs is larger or equal to the number of bits in self, the entire value is shifted out, and 0 is returned.

Examples

assert_eq!(0x1usize.unbounded_shl(4), 0x10);
assert_eq!(0x1usize.unbounded_shl(129), 0);

Exact shift left. Computes self << rhs as long as it can be reversed losslessly.

Returns None if any non-zero bits would be shifted out or if rhs >= usize::BITS. Otherwise, returns Some(self << rhs).

Examples

#![feature(exact_bitshifts)]

assert_eq!(0x1usize.shl_exact(4), Some(0x10));
assert_eq!(0x1usize.shl_exact(129), None);

Unchecked exact shift left. Computes self << rhs, assuming the operation can be losslessly reversed rhs cannot be larger than usize::BITS.

Safety

This results in undefined behavior when rhs > self.leading_zeros() || rhs >= usize::BITS i.e. when usize::shl_exact would return None.

Checked shift right. Computes self >> rhs, returning None if rhs is larger than or equal to the number of bits in self.

Examples

assert_eq!(0x10usize.checked_shr(4), Some(0x1));
assert_eq!(0x10usize.checked_shr(129), None);

Strict shift right. Computes self >> rhs, panicking if rhs is larger than or equal to the number of bits in self.

Panics

Overflow behavior

This function will always panic on overflow, regardless of whether overflow checks are enabled.

Examples

assert_eq!(0x10usize.strict_shr(4), 0x1);

The following panics because of overflow:

let _ = 0x10usize.strict_shr(129);

Unchecked shift right. Computes self >> rhs, assuming that rhs is less than the number of bits in self.

Safety

This results in undefined behavior if rhs is larger than or equal to the number of bits in self, i.e. when checked_shr would return None.

Unbounded shift right. Computes self >> rhs, without bounding the value of rhs.

If rhs is larger or equal to the number of bits in self, the entire value is shifted out, and 0 is returned.

Examples

assert_eq!(0x10usize.unbounded_shr(4), 0x1);
assert_eq!(0x10usize.unbounded_shr(129), 0);

Exact shift right. Computes self >> rhs as long as it can be reversed losslessly.

Returns None if any non-zero bits would be shifted out or if rhs >= usize::BITS. Otherwise, returns Some(self >> rhs).

Examples

#![feature(exact_bitshifts)]

assert_eq!(0x10usize.shr_exact(4), Some(0x1));
assert_eq!(0x10usize.shr_exact(5), None);

Unchecked exact shift right. Computes self >> rhs, assuming the operation can be losslessly reversed and rhs cannot be larger than usize::BITS.

Safety

This results in undefined behavior when rhs > self.trailing_zeros() || rhs >= usize::BITS i.e. when usize::shr_exact would return None.

Checked exponentiation. Computes self.pow(exp), returning None if overflow occurred.

Examples

assert_eq!(2usize.checked_pow(5), Some(32));
assert_eq!(0_usize.checked_pow(0), Some(1));
assert_eq!(usize::MAX.checked_pow(2), None);

Strict exponentiation. Computes self.pow(exp), panicking if overflow occurred.

Panics

Overflow behavior

This function will always panic on overflow, regardless of whether overflow checks are enabled.

Examples

assert_eq!(2usize.strict_pow(5), 32);
assert_eq!(0_usize.strict_pow(0), 1);

The following panics because of overflow:

let _ = usize::MAX.strict_pow(2);

Saturating integer addition. Computes self + rhs, saturating at the numeric bounds instead of overflowing.

Examples

assert_eq!(100usize.saturating_add(1), 101);
assert_eq!(usize::MAX.saturating_add(127), usize::MAX);

Saturating addition with a signed integer. Computes self + rhs, saturating at the numeric bounds instead of overflowing.

Examples

assert_eq!(1usize.saturating_add_signed(2), 3);
assert_eq!(1usize.saturating_add_signed(-2), 0);
assert_eq!((usize::MAX - 2).saturating_add_signed(4), usize::MAX);

Saturating integer subtraction. Computes self - rhs, saturating at the numeric bounds instead of overflowing.

Examples

assert_eq!(100usize.saturating_sub(27), 73);
assert_eq!(13usize.saturating_sub(127), 0);

Saturating integer subtraction. Computes self - rhs, saturating at the numeric bounds instead of overflowing.

Examples

assert_eq!(1usize.saturating_sub_signed(2), 0);
assert_eq!(1usize.saturating_sub_signed(-2), 3);
assert_eq!((usize::MAX - 2).saturating_sub_signed(-4), usize::MAX);

Saturating integer multiplication. Computes self * rhs, saturating at the numeric bounds instead of overflowing.

Examples

assert_eq!(2usize.saturating_mul(10), 20);
assert_eq!((usize::MAX).saturating_mul(10), usize::MAX);

Saturating integer division. Computes self / rhs, saturating at the numeric bounds instead of overflowing.

Panics

This function will panic if rhs is zero.

Examples

assert_eq!(5usize.saturating_div(2), 2);

Saturating integer exponentiation. Computes self.pow(exp), saturating at the numeric bounds instead of overflowing.

Examples

assert_eq!(4usize.saturating_pow(3), 64);
assert_eq!(0_usize.saturating_pow(0), 1);
assert_eq!(usize::MAX.saturating_pow(2), usize::MAX);

Wrapping (modular) addition. Computes self + rhs, wrapping around at the boundary of the type.

Examples

assert_eq!(200usize.wrapping_add(55), 255);
assert_eq!(200usize.wrapping_add(usize::MAX), 199);

Wrapping (modular) addition with a signed integer. Computes self + rhs, wrapping around at the boundary of the type.

Examples

assert_eq!(1usize.wrapping_add_signed(2), 3);
assert_eq!(1usize.wrapping_add_signed(-2), usize::MAX);
assert_eq!((usize::MAX - 2).wrapping_add_signed(4), 1);

Wrapping (modular) subtraction. Computes self - rhs, wrapping around at the boundary of the type.

Examples

assert_eq!(100usize.wrapping_sub(100), 0);
assert_eq!(100usize.wrapping_sub(usize::MAX), 101);

Wrapping (modular) subtraction with a signed integer. Computes self - rhs, wrapping around at the boundary of the type.

Examples

assert_eq!(1usize.wrapping_sub_signed(2), usize::MAX);
assert_eq!(1usize.wrapping_sub_signed(-2), 3);
assert_eq!((usize::MAX - 2).wrapping_sub_signed(-4), 1);

Wrapping (modular) multiplication. Computes self * rhs, wrapping around at the boundary of the type.

Examples

Please note that this example is shared among integer types, which is why u8 is used.

assert_eq!(10u8.wrapping_mul(12), 120);
assert_eq!(25u8.wrapping_mul(12), 44);

Wrapping (modular) division. Computes self / rhs.

Wrapped division on unsigned types is just normal division. There’s no way wrapping could ever happen. This function exists so that all operations are accounted for in the wrapping operations.

Panics

This function will panic if rhs is zero.

Examples

assert_eq!(100usize.wrapping_div(10), 10);

Wrapping Euclidean division. Computes self.div_euclid(rhs).

Wrapped division on unsigned types is just normal division. There’s no way wrapping could ever happen. This function exists so that all operations are accounted for in the wrapping operations. Since, for the positive integers, all common definitions of division are equal, this is exactly equal to self.wrapping_div(rhs).

Panics

This function will panic if rhs is zero.

Examples

assert_eq!(100usize.wrapping_div_euclid(10), 10);

Wrapping (modular) remainder. Computes self % rhs.

Wrapped remainder calculation on unsigned types is just the regular remainder calculation. There’s no way wrapping could ever happen. This function exists so that all operations are accounted for in the wrapping operations.

Panics

This function will panic if rhs is zero.

Examples

assert_eq!(100usize.wrapping_rem(10), 0);

Wrapping Euclidean modulo. Computes self.rem_euclid(rhs).

Wrapped modulo calculation on unsigned types is just the regular remainder calculation. There’s no way wrapping could ever happen. This function exists so that all operations are accounted for in the wrapping operations. Since, for the positive integers, all common definitions of division are equal, this is exactly equal to self.wrapping_rem(rhs).

Panics

This function will panic if rhs is zero.

Examples

assert_eq!(100usize.wrapping_rem_euclid(10), 0);

Wrapping (modular) negation. Computes -self, wrapping around at the boundary of the type.

Since unsigned types do not have negative equivalents all applications of this function will wrap (except for -0). For values smaller than the corresponding signed type’s maximum the result is the same as casting the corresponding signed value. Any larger values are equivalent to MAX + 1 - (val - MAX - 1) where MAX is the corresponding signed type’s maximum.

Examples

assert_eq!(0_usize.wrapping_neg(), 0);
assert_eq!(usize::MAX.wrapping_neg(), 1);
assert_eq!(13_usize.wrapping_neg(), (!13) + 1);
assert_eq!(42_usize.wrapping_neg(), !(42 - 1));

Panic-free bitwise shift-left; yields self << mask(rhs), where mask removes any high-order bits of rhs that would cause the shift to exceed the bitwidth of the type.

Note that this is not the same as a rotate-left; the RHS of a wrapping shift-left is restricted to the range of the type, rather than the bits shifted out of the LHS being returned to the other end. The primitive integer types all implement a rotate_left function, which may be what you want instead.

Examples

assert_eq!(1usize.wrapping_shl(7), 128);
assert_eq!(1usize.wrapping_shl(128), 1);

Panic-free bitwise shift-right; yields self >> mask(rhs), where mask removes any high-order bits of rhs that would cause the shift to exceed the bitwidth of the type.

Note that this is not the same as a rotate-right; the RHS of a wrapping shift-right is restricted to the range of the type, rather than the bits shifted out of the LHS being returned to the other end. The primitive integer types all implement a rotate_right function, which may be what you want instead.

Examples

assert_eq!(128usize.wrapping_shr(7), 1);
assert_eq!(128usize.wrapping_shr(128), 128);

Wrapping (modular) exponentiation. Computes self.pow(exp), wrapping around at the boundary of the type.

Examples

assert_eq!(3usize.wrapping_pow(5), 243);
assert_eq!(3u8.wrapping_pow(6), 217);
assert_eq!(0_usize.wrapping_pow(0), 1);

Calculates self + rhs.

Returns a tuple of the addition along with a boolean indicating whether an arithmetic overflow would occur. If an overflow would have occurred then the wrapped value is returned.

Examples

assert_eq!(5usize.overflowing_add(2), (7, false));
assert_eq!(usize::MAX.overflowing_add(1), (0, true));

Calculates self + rhs + carry and returns a tuple containing the sum and the output carry (in that order).

Performs “ternary addition” of two integer operands and a carry-in bit, and returns an output integer and a carry-out bit. This allows chaining together multiple additions to create a wider addition, and can be useful for bignum addition.

This can be thought of as a 64-bit “full adder”, in the electronics sense.

If the input carry is false, this method is equivalent to overflowing_add, and the output carry is equal to the overflow flag. Note that although carry and overflow flags are similar for unsigned integers, they are different for signed integers.

Examples

//    3  MAX    (a = 3 × 2^64 + 2^64 - 1)
// +  5    7    (b = 5 × 2^64 + 7)
// ---------
//    9    6    (sum = 9 × 2^64 + 6)

let (a1, a0): (usize, usize) = (3, usize::MAX);
let (b1, b0): (usize, usize) = (5, 7);
let carry0 = false;

let (sum0, carry1) = a0.carrying_add(b0, carry0);
assert_eq!(carry1, true);
let (sum1, carry2) = a1.carrying_add(b1, carry1);
assert_eq!(carry2, false);

assert_eq!((sum1, sum0), (9, 6));

Calculates self + rhs with a signed rhs.

Returns a tuple of the addition along with a boolean indicating whether an arithmetic overflow would occur. If an overflow would have occurred then the wrapped value is returned.

Examples

assert_eq!(1usize.overflowing_add_signed(2), (3, false));
assert_eq!(1usize.overflowing_add_signed(-2), (usize::MAX, true));
assert_eq!((usize::MAX - 2).overflowing_add_signed(4), (1, true));

Calculates self - rhs.

Returns a tuple of the subtraction along with a boolean indicating whether an arithmetic overflow would occur. If an overflow would have occurred then the wrapped value is returned.

Examples

assert_eq!(5usize.overflowing_sub(2), (3, false));
assert_eq!(0usize.overflowing_sub(1), (usize::MAX, true));

Calculates self − rhs − borrow and returns a tuple containing the difference and the output borrow.

Performs “ternary subtraction” by subtracting both an integer operand and a borrow-in bit from self, and returns an output integer and a borrow-out bit. This allows chaining together multiple subtractions to create a wider subtraction, and can be useful for bignum subtraction.

Examples

//    9    6    (a = 9 × 2^64 + 6)
// -  5    7    (b = 5 × 2^64 + 7)
// ---------
//    3  MAX    (diff = 3 × 2^64 + 2^64 - 1)

let (a1, a0): (usize, usize) = (9, 6);
let (b1, b0): (usize, usize) = (5, 7);
let borrow0 = false;

let (diff0, borrow1) = a0.borrowing_sub(b0, borrow0);
assert_eq!(borrow1, true);
let (diff1, borrow2) = a1.borrowing_sub(b1, borrow1);
assert_eq!(borrow2, false);

assert_eq!((diff1, diff0), (3, usize::MAX));

Calculates self - rhs with a signed rhs

Returns a tuple of the subtraction along with a boolean indicating whether an arithmetic overflow would occur. If an overflow would have occurred then the wrapped value is returned.

Examples

assert_eq!(1usize.overflowing_sub_signed(2), (usize::MAX, true));
assert_eq!(1usize.overflowing_sub_signed(-2), (3, false));
assert_eq!((usize::MAX - 2).overflowing_sub_signed(-4), (1, true));

Computes the absolute difference between self and other.

Examples

assert_eq!(100usize.abs_diff(80), 20usize);
assert_eq!(100usize.abs_diff(110), 10usize);

Calculates the multiplication of self and rhs.

Returns a tuple of the multiplication along with a boolean indicating whether an arithmetic overflow would occur. If an overflow would have occurred then the wrapped value is returned.

If you want the value of the overflow, rather than just whether an overflow occurred, see Self::carrying_mul.

Examples

Please note that this example is shared among integer types, which is why u32 is used.

assert_eq!(5u32.overflowing_mul(2), (10, false));
assert_eq!(1_000_000_000u32.overflowing_mul(10), (1410065408, true));

Calculates the complete double-width product self * rhs.

This returns the low-order (wrapping) bits and the high-order (overflow) bits of the result as two separate values, in that order. As such, a.widening_mul(b).0 produces the same result as a.wrapping_mul(b).

If you also need to add a value and carry to the wide result, then you want Self::carrying_mul_add instead.

If you also need to add a carry to the wide result, then you want Self::carrying_mul instead.

If you just want to know whether the multiplication overflowed, then you want Self::overflowing_mul instead.

Examples

#![feature(bigint_helper_methods)]
assert_eq!(5_usize.widening_mul(7), (35, 0));
assert_eq!(usize::MAX.widening_mul(usize::MAX), (1, usize::MAX - 1));

Compared to other *_mul methods:

#![feature(bigint_helper_methods)]
assert_eq!(usize::widening_mul(1 << 63, 6), (0, 3));
assert_eq!(usize::overflowing_mul(1 << 63, 6), (0, true));
assert_eq!(usize::wrapping_mul(1 << 63, 6), 0);
assert_eq!(usize::checked_mul(1 << 63, 6), None);

Please note that this example is shared among integer types, which is why u32 is used.

#![feature(bigint_helper_methods)]
assert_eq!(5u32.widening_mul(2), (10, 0));
assert_eq!(1_000_000_000u32.widening_mul(10), (1410065408, 2));

Calculates the “full multiplication” self * rhs + carry without the possibility to overflow.

This returns the low-order (wrapping) bits and the high-order (overflow) bits of the result as two separate values, in that order.

Performs “long multiplication” which takes in an extra amount to add, and may return an additional amount of overflow. This allows for chaining together multiple multiplications to create “big integers” which represent larger values.

If you also need to add a value, then use Self::carrying_mul_add.

Examples

Please note that this example is shared among integer types, which is why u32 is used.

assert_eq!(5u32.carrying_mul(2, 0), (10, 0));
assert_eq!(5u32.carrying_mul(2, 10), (20, 0));
assert_eq!(1_000_000_000u32.carrying_mul(10, 0), (1410065408, 2));
assert_eq!(1_000_000_000u32.carrying_mul(10, 10), (1410065418, 2));
assert_eq!(usize::MAX.carrying_mul(usize::MAX, usize::MAX), (0, usize::MAX));

This is the core operation needed for scalar multiplication when implementing it for wider-than-native types.

#![feature(bigint_helper_methods)]
fn scalar_mul_eq(little_endian_digits: &mut Vec<u16>, multiplicand: u16) {
    let mut carry = 0;
    for d in little_endian_digits.iter_mut() {
        (*d, carry) = d.carrying_mul(multiplicand, carry);
    }
    if carry != 0 {
        little_endian_digits.push(carry);
    }
}

let mut v = vec![10, 20];
scalar_mul_eq(&mut v, 3);
assert_eq!(v, [30, 60]);

assert_eq!(0x87654321_u64 * 0xFEED, 0x86D3D159E38D);
let mut v = vec![0x4321, 0x8765];
scalar_mul_eq(&mut v, 0xFEED);
assert_eq!(v, [0xE38D, 0xD159, 0x86D3]);

If carry is zero, this is similar to overflowing_mul, except that it gives the value of the overflow instead of just whether one happened:

#![feature(bigint_helper_methods)]
let r = u8::carrying_mul(7, 13, 0);
assert_eq!((r.0, r.1 != 0), u8::overflowing_mul(7, 13));
let r = u8::carrying_mul(13, 42, 0);
assert_eq!((r.0, r.1 != 0), u8::overflowing_mul(13, 42));

The value of the first field in the returned tuple matches what you’d get by combining the wrapping_mul and wrapping_add methods:

#![feature(bigint_helper_methods)]
assert_eq!(
    789_u16.carrying_mul(456, 123).0,
    789_u16.wrapping_mul(456).wrapping_add(123),
);

Calculates the “full multiplication” self * rhs + carry + add.

This returns the low-order (wrapping) bits and the high-order (overflow) bits of the result as two separate values, in that order.

This cannot overflow, as the double-width result has exactly enough space for the largest possible result. This is equivalent to how, in decimal, 9 × 9 + 9 + 9 = 81 + 18 = 99 = 9×10⁰ + 9×10¹ = 10² - 1.

Performs “long multiplication” which takes in an extra amount to add, and may return an additional amount of overflow. This allows for chaining together multiple multiplications to create “big integers” which represent larger values.

If you don’t need the add part, then you can use Self::carrying_mul instead.

Examples

Please note that this example is shared between integer types, which explains why u32 is used here.

assert_eq!(5u32.carrying_mul_add(2, 0, 0), (10, 0));
assert_eq!(5u32.carrying_mul_add(2, 10, 10), (30, 0));
assert_eq!(1_000_000_000u32.carrying_mul_add(10, 0, 0), (1410065408, 2));
assert_eq!(1_000_000_000u32.carrying_mul_add(10, 10, 10), (1410065428, 2));
assert_eq!(usize::MAX.carrying_mul_add(usize::MAX, usize::MAX, usize::MAX), (usize::MAX, usize::MAX));

This is the core per-digit operation for “grade school” O(n²) multiplication.

Please note that this example is shared between integer types, using u8 for simplicity of the demonstration.

fn quadratic_mul<const N: usize>(a: [u8; N], b: [u8; N]) -> [u8; N] {
    let mut out = [0; N];
    for j in 0..N {
        let mut carry = 0;
        for i in 0..(N - j) {
            (out[j + i], carry) = u8::carrying_mul_add(a[i], b[j], out[j + i], carry);
        }
    }
    out
}

// -1 * -1 == 1
assert_eq!(quadratic_mul([0xFF; 3], [0xFF; 3]), [1, 0, 0]);

assert_eq!(u32::wrapping_mul(0x9e3779b9, 0x7f4a7c15), 0xcffc982d);
assert_eq!(
    quadratic_mul(u32::to_le_bytes(0x9e3779b9), u32::to_le_bytes(0x7f4a7c15)),
    u32::to_le_bytes(0xcffc982d)
);

Calculates the divisor when self is divided by rhs.

Returns a tuple of the divisor along with a boolean indicating whether an arithmetic overflow would occur. Note that for unsigned integers overflow never occurs, so the second value is always false.

Panics

This function will panic if rhs is zero.

Examples

assert_eq!(5usize.overflowing_div(2), (2, false));

Calculates the quotient of Euclidean division self.div_euclid(rhs).

Returns a tuple of the divisor along with a boolean indicating whether an arithmetic overflow would occur. Note that for unsigned integers overflow never occurs, so the second value is always false. Since, for the positive integers, all common definitions of division are equal, this is exactly equal to self.overflowing_div(rhs).

Panics

This function will panic if rhs is zero.

Examples

assert_eq!(5usize.overflowing_div_euclid(2), (2, false));

Calculates the remainder when self is divided by rhs.

Returns a tuple of the remainder after dividing along with a boolean indicating whether an arithmetic overflow would occur. Note that for unsigned integers overflow never occurs, so the second value is always false.

Panics

This function will panic if rhs is zero.

Examples

assert_eq!(5usize.overflowing_rem(2), (1, false));

Calculates the remainder self.rem_euclid(rhs) as if by Euclidean division.

Returns a tuple of the modulo after dividing along with a boolean indicating whether an arithmetic overflow would occur. Note that for unsigned integers overflow never occurs, so the second value is always false. Since, for the positive integers, all common definitions of division are equal, this operation is exactly equal to self.overflowing_rem(rhs).

Panics

This function will panic if rhs is zero.

Examples

assert_eq!(5usize.overflowing_rem_euclid(2), (1, false));

Negates self in an overflowing fashion.

Returns !self + 1 using wrapping operations to return the value that represents the negation of this unsigned value. Note that for positive unsigned values overflow always occurs, but negating 0 does not overflow.

Examples

assert_eq!(0usize.overflowing_neg(), (0, false));
assert_eq!(2usize.overflowing_neg(), (-2i32 as usize, true));

Shifts self left by rhs bits.

Returns a tuple of the shifted version of self along with a boolean indicating whether the shift value was larger than or equal to the number of bits. If the shift value is too large, then value is masked (N-1) where N is the number of bits, and this value is then used to perform the shift.

Examples

assert_eq!(0x1usize.overflowing_shl(4), (0x10, false));
assert_eq!(0x1usize.overflowing_shl(132), (0x10, true));
assert_eq!(0x10usize.overflowing_shl(63), (0, false));

Shifts self right by rhs bits.

Returns a tuple of the shifted version of self along with a boolean indicating whether the shift value was larger than or equal to the number of bits. If the shift value is too large, then value is masked (N-1) where N is the number of bits, and this value is then used to perform the shift.

Examples

assert_eq!(0x10usize.overflowing_shr(4), (0x1, false));
assert_eq!(0x10usize.overflowing_shr(132), (0x1, true));

Raises self to the power of exp, using exponentiation by squaring.

Returns a tuple of the exponentiation along with a bool indicating whether an overflow happened.

Examples

assert_eq!(3usize.overflowing_pow(5), (243, false));
assert_eq!(0_usize.overflowing_pow(0), (1, false));
assert_eq!(3u8.overflowing_pow(6), (217, true));

Raises self to the power of exp, using exponentiation by squaring.

Examples

assert_eq!(2usize.pow(5), 32);
assert_eq!(0_usize.pow(0), 1);

Returns the square root of the number, rounded down.

Examples

assert_eq!(10usize.isqrt(), 3);

Performs Euclidean division.

Since, for the positive integers, all common definitions of division are equal, this is exactly equal to self / rhs.

Panics

This function will panic if rhs is zero.

Examples

assert_eq!(7usize.div_euclid(4), 1); // or any other integer type

Calculates the least remainder of self (mod rhs).

Since, for the positive integers, all common definitions of division are equal, this is exactly equal to self % rhs.

Panics

This function will panic if rhs is zero.

Examples

assert_eq!(7usize.rem_euclid(4), 3); // or any other integer type

Calculates the quotient of self and rhs, rounding the result towards negative infinity.

This is the same as performing self / rhs for all unsigned integers.

Panics

This function will panic if rhs is zero.

Examples

#![feature(int_roundings)]
assert_eq!(7_usize.div_floor(4), 1);

Calculates the quotient of self and rhs, rounding the result towards positive infinity.

Panics

This function will panic if rhs is zero.

Examples

assert_eq!(7_usize.div_ceil(4), 2);

Calculates the smallest value greater than or equal to self that is a multiple of rhs.

Panics

This function will panic if rhs is zero.

Overflow behavior

On overflow, this function will panic if overflow checks are enabled (default in debug mode) and wrap if overflow checks are disabled (default in release mode).

Examples

assert_eq!(16_usize.next_multiple_of(8), 16);
assert_eq!(23_usize.next_multiple_of(8), 24);

Calculates the smallest value greater than or equal to self that is a multiple of rhs. Returns None if rhs is zero or the operation would result in overflow.

Examples

assert_eq!(16_usize.checked_next_multiple_of(8), Some(16));
assert_eq!(23_usize.checked_next_multiple_of(8), Some(24));
assert_eq!(1_usize.checked_next_multiple_of(0), None);
assert_eq!(usize::MAX.checked_next_multiple_of(2), None);

Returns true if self is an integer multiple of rhs, and false otherwise.

This function is equivalent to self % rhs == 0, except that it will not panic for rhs == 0. Instead, 0.is_multiple_of(0) == true, and for any non-zero n, n.is_multiple_of(0) == false.

Examples

assert!(6_usize.is_multiple_of(2));
assert!(!5_usize.is_multiple_of(2));

assert!(0_usize.is_multiple_of(0));
assert!(!6_usize.is_multiple_of(0));

Returns true if and only if self == 2^k for some unsigned integer k.

Examples

assert!(16usize.is_power_of_two());
assert!(!10usize.is_power_of_two());

Returns the smallest power of two greater than or equal to self.

When return value overflows (i.e., self > (1 << (N-1)) for type uN), it panics in debug mode and the return value is wrapped to 0 in release mode (the only situation in which this method can return 0).

Examples

assert_eq!(2usize.next_power_of_two(), 2);
assert_eq!(3usize.next_power_of_two(), 4);
assert_eq!(0usize.next_power_of_two(), 1);

Returns the smallest power of two greater than or equal to self. If the next power of two is greater than the type’s maximum value, None is returned, otherwise the power of two is wrapped in Some.

Examples

assert_eq!(2usize.checked_next_power_of_two(), Some(2));
assert_eq!(3usize.checked_next_power_of_two(), Some(4));
assert_eq!(usize::MAX.checked_next_power_of_two(), None);

Returns the smallest power of two greater than or equal to n. If the next power of two is greater than the type’s maximum value, the return value is wrapped to 0.

Examples

#![feature(wrapping_next_power_of_two)]

assert_eq!(2usize.wrapping_next_power_of_two(), 2);
assert_eq!(3usize.wrapping_next_power_of_two(), 4);
assert_eq!(usize::MAX.wrapping_next_power_of_two(), 0);

Returns the memory representation of this integer as a byte array in big-endian (network) byte order.

Note: This function returns an array of length 2, 4 or 8 bytes depending on the target pointer size.

Examples

let bytes = 0x1234567890123456usize.to_be_bytes();
assert_eq!(bytes, [0x12, 0x34, 0x56, 0x78, 0x90, 0x12, 0x34, 0x56]);

Returns the memory representation of this integer as a byte array in little-endian byte order.

Note: This function returns an array of length 2, 4 or 8 bytes depending on the target pointer size.

Examples

let bytes = 0x1234567890123456usize.to_le_bytes();
assert_eq!(bytes, [0x56, 0x34, 0x12, 0x90, 0x78, 0x56, 0x34, 0x12]);

Returns the memory representation of this integer as a byte array in native byte order.

As the target platform’s native endianness is used, portable code should use to_be_bytes or to_le_bytes, as appropriate, instead.

Note: This function returns an array of length 2, 4 or 8 bytes depending on the target pointer size.

Examples

let bytes = 0x1234567890123456usize.to_ne_bytes();
assert_eq!(
    bytes,
    if cfg!(target_endian = "big") {
        [0x12, 0x34, 0x56, 0x78, 0x90, 0x12, 0x34, 0x56]
    } else {
        [0x56, 0x34, 0x12, 0x90, 0x78, 0x56, 0x34, 0x12]
    }
);

Creates a native endian integer value from its representation as a byte array in big endian.

Note: This function takes an array of length 2, 4 or 8 bytes depending on the target pointer size.

Examples

let value = usize::from_be_bytes([0x12, 0x34, 0x56, 0x78, 0x90, 0x12, 0x34, 0x56]);
assert_eq!(value, 0x1234567890123456);

When starting from a slice rather than an array, fallible conversion APIs can be used:

fn read_be_usize(input: &mut &[u8]) -> usize {
    let (int_bytes, rest) = input.split_at(size_of::<usize>());
    *input = rest;
    usize::from_be_bytes(int_bytes.try_into().unwrap())
}

Creates a native endian integer value from its representation as a byte array in little endian.

Note: This function takes an array of length 2, 4 or 8 bytes depending on the target pointer size.

Examples

let value = usize::from_le_bytes([0x56, 0x34, 0x12, 0x90, 0x78, 0x56, 0x34, 0x12]);
assert_eq!(value, 0x1234567890123456);

When starting from a slice rather than an array, fallible conversion APIs can be used:

fn read_le_usize(input: &mut &[u8]) -> usize {
    let (int_bytes, rest) = input.split_at(size_of::<usize>());
    *input = rest;
    usize::from_le_bytes(int_bytes.try_into().unwrap())
}

Creates a native endian integer value from its memory representation as a byte array in native endianness.

As the target platform’s native endianness is used, portable code likely wants to use from_be_bytes or from_le_bytes, as appropriate instead.

Note: This function takes an array of length 2, 4 or 8 bytes depending on the target pointer size.

Examples

let value = usize::from_ne_bytes(if cfg!(target_endian = "big") {
    [0x12, 0x34, 0x56, 0x78, 0x90, 0x12, 0x34, 0x56]
} else {
    [0x56, 0x34, 0x12, 0x90, 0x78, 0x56, 0x34, 0x12]
});
assert_eq!(value, 0x1234567890123456);

When starting from a slice rather than an array, fallible conversion APIs can be used:

fn read_ne_usize(input: &mut &[u8]) -> usize {
    let (int_bytes, rest) = input.split_at(size_of::<usize>());
    *input = rest;
    usize::from_ne_bytes(int_bytes.try_into().unwrap())
}

New code should prefer to use usize::MIN instead.

Returns the smallest value that can be represented by this integer type.

New code should prefer to use usize::MAX instead.

Returns the largest value that can be represented by this integer type.

Calculates the midpoint (average) between self and rhs.

midpoint(a, b) is (a + b) / 2 as if it were performed in a sufficiently-large unsigned integral type. This implies that the result is always rounded towards zero and that no overflow will ever occur.

Examples

assert_eq!(0usize.midpoint(4), 2);
assert_eq!(1usize.midpoint(4), 2);

Parses an integer from a string slice with digits in a given base.

The string is expected to be an optional + sign followed by only digits. Leading and trailing non-digit characters (including whitespace) represent an error. Underscores (which are accepted in Rust literals) also represent an error.

Digits are a subset of these characters, depending on radix:

• 0-9
• a-z
• A-Z

Panics

This function panics if radix is not in the range from 2 to 36.

See also

If the string to be parsed is in base 10 (decimal), from_str or str::parse can also be used.

Examples

assert_eq!(usize::from_str_radix("A", 16), Ok(10));

Trailing space returns error:

assert!(usize::from_str_radix("1 ", 10).is_err());

Parses an integer from an ASCII-byte slice with decimal digits.

The characters are expected to be an optional + sign followed by only digits. Leading and trailing non-digit characters (including whitespace) represent an error. Underscores (which are accepted in Rust literals) also represent an error.

Examples

#![feature(int_from_ascii)]

assert_eq!(usize::from_ascii(b"+10"), Ok(10));

Trailing space returns error:

assert!(usize::from_ascii(b"1 ").is_err());

Parses an integer from an ASCII-byte slice with digits in a given base.

The characters are expected to be an optional + sign followed by only digits. Leading and trailing non-digit characters (including whitespace) represent an error. Underscores (which are accepted in Rust literals) also represent an error.

Digits are a subset of these characters, depending on radix:

• 0-9
• a-z
• A-Z

Panics

This function panics if radix is not in the range from 2 to 36.

Examples

#![feature(int_from_ascii)]

assert_eq!(usize::from_ascii_radix(b"A", 16), Ok(10));

Trailing space returns error:

assert!(usize::from_ascii_radix(b"1 ", 10).is_err());

Allows users to write an integer (in signed decimal format) into a variable buf of type NumBuffer that is passed by the caller by mutable reference.

Examples

#![feature(int_format_into)]
use core::fmt::NumBuffer;

let n = 0usize;
let mut buf = NumBuffer::new();
assert_eq!(n.format_into(&mut buf), "0");

let n1 = 32usize;
assert_eq!(n1.format_into(&mut buf), "32");

let n2 = usize :: MAX;
assert_eq!(n2.format_into(&mut buf), usize :: MAX.to_string());

Format unsigned integers in the radix.

Returns the default value of 0

Same as self / other.get(), but because other is a NonZero<_>, there’s never a runtime check for division-by-zero.

This operation rounds towards zero, truncating any fractional part of the exact result, and cannot panic.

Same as self /= other.get(), but because other is a NonZero<_>, there’s never a runtime check for division-by-zero.

This operation rounds towards zero, truncating any fractional part of the exact result, and cannot panic.

Converts a bool to usize losslessly. The resulting value is 0 for false and 1 for true values.

Examples

assert_eq!(usize::from(true), 1);
assert_eq!(usize::from(false), 0);

Converts u16 to usize losslessly.

Converts u8 to usize losslessly.

Converts an usize into an AtomicUsize.

Parses an integer from a string slice with decimal digits.

The characters are expected to be an optional + sign followed by only digits. Leading and trailing non-digit characters (including whitespace) represent an error. Underscores (which are accepted in Rust literals) also represent an error.

See also

For parsing numbers in other bases, such as binary or hexadecimal, see from_str_radix.

Examples

use std::str::FromStr;

assert_eq!(usize::from_str("+10"), Ok(10));

Trailing space returns error:

assert!(usize::from_str("1 ").is_err());

Format unsigned integers in the radix.

Format unsigned integers in the radix.

This operation satisfies n % d == n - (n / d) * d, and cannot panic.

This operation satisfies n % d == n - (n / d) * d, and cannot panic.