php trim函数是怎么实现的

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PHP Warning:  trim(): Invalid '..'-range, no character to the left of '..' in Command line code on line 1
Warning: trim(): Invalid '..'-range, no character to the left of '..' in Command line code on line 1
PHP Warning:  trim(): Invalid '..'-range, no character to the right of '..' inCommand line code on line 1
Warning: trim(): Invalid '..'-range, no character to the right of '..' in Command line code on line 1

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PHP_FUNCTION(trim)
{
    php_do_trim(INTERNAL_FUNCTION_PARAM_PASSTHRU, 3);
}

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static void php_do_trim(INTERNAL_FUNCTION_PARAMETERS, int mode)
{
    char *str;
    char *what = NULL;
    int str_len, what_len = 0;
    if (zend_parse_parameters(ZEND_NUM_ARGS() TSRM_CC, "s|s", &str, &str_len, &what, &what_len) == FAILURE) {
        return;
    } 
    php_trim(str, str_len, what, what_len, return_value, mode TSRMLS_CC);
}

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PHPAPI char *php_trim(char *c, int len, char *what, int what_len, zval *return_value, int mode TSRMLS_DC)
{
    register int i;
    int trimmed = 0;
    char mask[256];
    
        if(what) {
            php_charmask((unsigned char*)what, what_len, mask TSRMLS_CC);
        } else {
            php_charmask((unsigned char*)" nrtv", 6, mask TSRMLS_CC);
        }

        if (mode & 1) {
            for (i = 0; i = 0; i--) {
                if (mask[(unsigned char)c[i]]) {
                    len--;
                } else {
                    break;
                }
            }
        }

        if (return_value) {
            RETVAL_STRINGL(c, len, 1);
        } else {
            return estrndup(c, len);
        }
        return "";
}

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static inline int php_charmask(unsigned char *input, int len, char *mask TSRMLS_DC)
{
    unsigned char *end;
    unsigned char c;
    int result = SUCCESS;
    memset(mask, 0, 256);
    for (end = input+len; input = c) { 
            memset(mask+c, 1, input[3] - c + 1);
            input+=3;
        } else if ((input+1 = input) { /* there was no 'left' char */
                php_error_docref(NULL TSRMLS_CC, E_WARNING, "Invalid '..'-range, no character to the left of '..'");
                result = FAILURE;
                continue;
            }
            if (input+2 >= end) { /* there is no 'right' char */
                php_error_docref(NULL TSRMLS_CC, E_WARNING, "Invalid '..'-range, no character to the right of '..'");
                result = FAILURE;
                continue;
            }
            if (input[-1] > input[2]) { /* wrong order */
                php_error_docref(NULL TSRMLS_CC, E_WARNING, "Invalid '..'-range, '..'-range needs to be incrementing");
                result = FAILURE;
                continue;
            }
            /* FIXME: better error (a..b..c is the only left possibility?) */
            php_error_docref(NULL TSRMLS_CC, E_WARNING, "Invalid '..'-range");
            result = FAILURE;
            continue;
        } else {
            mask[c]=1;
        }
    }    
    return result;
}

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mask['a'] = 1;
    mask['b'] = 1;
    mask['c'] = 1;

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#includeint main(){
     printf("%dn",1&1);
     printf("%dn",2&2);
     printf("%dn",3&1);
     printf("%dn",3&2);
     return 0;
}

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1
2

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for (i = 0; i

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for (i = len - 1; i >= 0; i--) {
    if (mask[(unsigned char)c[i]]) {
        len--;
    } else {
        break;
    }
}

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if (return_value) {
   RETVAL_STRINGL(c, len, 1);
} else {
   return estrndup(c, len);
}