php，谁能帮我解释下这个代码

PHP_FUNCTION(bcdiv)
{
char *left, *right;
size_t left_len, right_len;
zend_long scale_param = 0;
bc_num first, second, result;
int scale = (int)BCG(bc_precision), argc = ZEND_NUM_ARGS();

if (zend_parse_parameters(argc, "ss|l", &left, &left_len, &right, &right_len, &scale_param) == FAILURE) {
    return;
}

if (argc == 3) {
    scale = (int) ((int)scale_param < 0 ? 0 : scale_param);
}

bc_init_num(&first);
bc_init_num(&second);
bc_init_num(&result);
php_str2num(&first, left);
php_str2num(&second, right);

switch (bc_divide(first, second, &result, scale)) {
    case 0: /* OK */
        if (result->n_scale > scale) {
            result = split_bc_num(result);
            result->n_scale = scale;
        }
        RETVAL_STR(bc_num2str(result));
        break;
    case -1: /* division by zero */
        php_error_docref(NULL, E_WARNING, "Division by zero");
        break;
}

bc_free_num(&first);
bc_free_num(&second);
bc_free_num(&result);
return;

}
/* }}} */

/* {{{ proto string bcmod(string left_operand, string right_operand)
Returns the modulus of the two arbitrary precision operands */
PHP_FUNCTION(bcmod)
{
char *left, *right;
size_t left_len, right_len;
bc_num first, second, result;

if (zend_parse_parameters(ZEND_NUM_ARGS(), "ss", &left, &left_len, &right, &right_len) == FAILURE) {
    return;
}

bc_init_num(&first);
bc_init_num(&second);
bc_init_num(&result);
bc_str2num(&first, left, 0);
bc_str2num(&second, right, 0);

switch (bc_modulo(first, second, &result, 0)) {
    case 0:
        RETVAL_STR(bc_num2str(result));
        break;
    case -1:
        php_error_docref(NULL, E_WARNING, "Division by zero");
        break;
}

bc_free_num(&first);
bc_free_num(&second);
bc_free_num(&result);
return;

}

这是C++代码，不是php的。应该是用c++写php扩展模块。