原型

_hash_hmac( $algo,  $data,  $key,  $raw_output = false )

源文件

路径:wp-includes/compat.php

<?php
...
 *
 * @param string      $str      The string to retrieve the character length from.
 * @param string|null $encoding Optional. Character encoding to use. Default null.
 * @return int String length of `$str`.
 */
function _mb_strlen( $str, $encoding = null ) {
	if ( null === $encoding ) {
		$encoding = get_option( 'blog_charset' );
	}
	/*
	 * The solution below works only for UTF-8, so in case of a different charset
	 * just use built-in strlen().
	 */
	if ( ! in_array( $encoding, array( 'utf8', 'utf-8', 'UTF8', 'UTF-8' ) ) ) {
		return strlen( $str );
	}
	if ( _wp_can_use_pcre_u() ) {
		// Use the regex unicode support to separate the UTF-8 characters into an array.
		preg_match_all( '/./us', $str, $match );
		return count( $match[0] );
...
?>

其他

英文文档:https://developer.wordpress.org/reference/functions/_hash_hmac/