redis源码阅读之util

这两个文件是用来提供一些公用函数的，首当其冲的就是类正则表达式的stringmatchlen函数，看了之后感觉是豁然开朗，感觉对正则表达式的实现多了点理解，又可以去LeetCode装x了~~自己惦着脸加了点中文注释：-）

int stringmatchlen(const char *pattern, int patternLen, const char *string, int stringLen, int nocase)
{
    while(patternLen) {
        switch(pattern[0]) {
        case '*':
            while (pattern[1] == '*') {
                pattern++;
                patternLen--;
            }
            if (patternLen == 1)
                return 1; /* match */
            while(stringLen) {
            /*关于正则当中的'*'，只管匹配其后的模式即可，只要有一次匹配，即可匹配，所以下面用了递归*/
                if (stringmatchlen(pattern+1, patternLen-1,
                            string, stringLen, nocase))
                    return 1; /* match */
                string++;
                stringLen--;
            }
            return 0; /* no match */
            break;
        case '?':/* ?表示0次或者1次，直接跳过 */
            if (stringLen == 0)
                return 0; /* no match */
            string++;
            stringLen--;
            break;
        case '[':
        {
            int not, match;

            pattern++;
            patternLen--;
            not = pattern[0] == '^';
            if (not) {
                pattern++;
                patternLen--;
            }
            match = 0;
            while(1) {/*方括号的话，最好在自己的内部完成是否匹配，所以这边用了死循环*/
                if (pattern[0] == '\\' && patternLen >= 2) {
                    pattern++;
                    patternLen--;
                    if (pattern[0] == string[0])
                        match = 1;
                }
                else if (pattern[0] == ']') {
                    break;
                }
                else if (patternLen == 0) {
                    pattern--;
                    patternLen++;
                    break;
                }
                else if (pattern[1] == '-' && patternLen >= 3) {
                    int start = pattern[0];
                    int end = pattern[2];
                    int c = string[0];
                    if (start > end) {
                        int t = start;
                        start = end;
                        end = t;
                    }
                    if (nocase) {
                        start = tolower(start);
                        end = tolower(end);
                        c = tolower(c);
                    }
                    pattern += 2;
                    patternLen -= 2;
                    if (c >= start && c <= end)
                        match = 1;
                }
                else {
                    if (!nocase) {
                        if (pattern[0] == string[0])
                            match = 1;
                    } else {
                        if (tolower((int)pattern[0]) == tolower((int)string[0]))
                            match = 1;
                    }
                }
                pattern++;
                patternLen--;
            }
            if (not)
                match = !match;
            if (!match)
                return 0; /* no match */
            string++;
            stringLen--;
            break;
        }
        case '\\':
            if (patternLen >= 2) {
                pattern++;
                patternLen--;
            }
            /* fall through */
        default:/*默认情况直接匹配*/
            if (!nocase) {
                if (pattern[0] != string[0])
                    return 0; /* no match */
            } else {
                if (tolower((int)pattern[0]) != tolower((int)string[0]))
                    return 0; /* no match */
            }
            string++;
            stringLen--;
            break;
        }
        pattern++;
        patternLen--;
        if (stringLen == 0) {
            while(*pattern == '*') {
                pattern++;
                patternLen--;
            }
            break;
        }
    }
    if (patternLen == 0 && stringLen == 0)
        return 1;
    return 0;
}

接下来比较有意思的就是ll2string函数了，它是两位两位的除以100，而不是像想象的那样一位一位的除以10，并且它还将对应关系实现存在了一个数组里面，值得借鉴~~

int ll2string(char *dst, size_t dstlen, long long svalue) {
    static const char digits[201] =
        "0001020304050607080910111213141516171819"
        "2021222324252627282930313233343536373839"
        "4041424344454647484950515253545556575859"
        "6061626364656667686970717273747576777879"
        "8081828384858687888990919293949596979899";
    int negative;
    unsigned long long value;

    /* The main loop works with 64bit unsigned integers for simplicity, so
     * we convert the number here and remember if it is negative. */
    if (svalue < 0) {
        if (svalue != LLONG_MIN) {
            value = -svalue;
        } else {
            value = ((unsigned long long) LLONG_MAX)+1;
        }
        negative = 1;
    } else {
        value = svalue;
        negative = 0;
    }

    /* Check length. */
    uint32_t const length = digits10(value)+negative;
    if (length >= dstlen) return 0;

    /* Null term. */
    uint32_t next = length;
    dst[next] = '\0';
    next--;
    while (value >= 100) {
        int const i = (value % 100) * 2;
        value /= 100;
        dst[next] = digits[i + 1];
        dst[next - 1] = digits[i];
        next -= 2;
    }

    /* Handle last 1-2 digits. */
    if (value < 10) {
        dst[next] = '0' + (uint32_t) value;
    } else {
        int i = (uint32_t) value * 2;
        dst[next] = digits[i + 1];
        dst[next - 1] = digits[i];
    }

    /* Add sign. */
    if (negative) dst[0] = '-';
    return length;
}

之后其他的string和double类型的互转都用到了atol和snprintf等库函数，这里暂且不表