Source

File: wp-includes/Requests/IDNAEncoder.php

protected static function utf8_to_codepoints($input) {
		$codepoints = array();

		// Get number of bytes
		$strlen = strlen($input);

		for ($position = 0; $position < $strlen; $position++) {
			$value = ord($input[$position]);

			// One byte sequence:
			if ((~$value & 0x80) === 0x80) {
				$character = $value;
				$length = 1;
				$remaining = 0;
			}
			// Two byte sequence:
			elseif (($value & 0xE0) === 0xC0) {
				$character = ($value & 0x1F) << 6;
				$length = 2;
				$remaining = 1;
			}
			// Three byte sequence:
			elseif (($value & 0xF0) === 0xE0) {
				$character = ($value & 0x0F) << 12;
				$length = 3;
				$remaining = 2;
			}
			// Four byte sequence:
			elseif (($value & 0xF8) === 0xF0) {
				$character = ($value & 0x07) << 18;
				$length = 4;
				$remaining = 3;
			}
			// Invalid byte:
			else {
				throw new Requests_Exception('Invalid Unicode codepoint', 'idna.invalidcodepoint', $value);
			}

			if ($remaining > 0) {
				if ($position + $length > $strlen) {
					throw new Requests_Exception('Invalid Unicode codepoint', 'idna.invalidcodepoint', $character);
				}
				for ($position++; $remaining > 0; $position++) {
					$value = ord($input[$position]);

					// If it is invalid, count the sequence as invalid and reprocess the current byte:
					if (($value & 0xC0) !== 0x80) {
						throw new Requests_Exception('Invalid Unicode codepoint', 'idna.invalidcodepoint', $character);
					}

					$character |= ($value & 0x3F) << (--$remaining * 6);
				}
				$position--;
			}

			if (
				// Non-shortest form sequences are invalid
				   $length > 1 && $character <= 0x7F
				|| $length > 2 && $character <= 0x7FF
				|| $length > 3 && $character <= 0xFFFF
				// Outside of range of ucschar codepoints
				// Noncharacters
				|| ($character & 0xFFFE) === 0xFFFE
				|| $character >= 0xFDD0 && $character <= 0xFDEF
				|| (
					// Everything else not in ucschar
					   $character > 0xD7FF && $character < 0xF900
					|| $character < 0x20
					|| $character > 0x7E && $character < 0xA0
					|| $character > 0xEFFFD
				)
			) {
				throw new Requests_Exception('Invalid Unicode codepoint', 'idna.invalidcodepoint', $character);
			}

			$codepoints[] = $character;
		}

		return $codepoints;
	}