转换字符大小写（Nginx、PHP、Redis源码）

剖析源码中如何做

Nginx源码中转换字符大小写

/*
 * 字符范围 十进制表示  二进制表示
 *   A-Z      65-90     0100 0001 - 0101 1010
 *   a-z      97-122    0110 0001 - 0111 1010
 *  由于0x20(2^6)该位在大写二进制中是0，小写二进制中是1
 *  则利用 | 将大写改为小写
 *  则利用 & ~0x20 将小写改为大写
 */
#define ngx_tolower(c)      (u_char) ((c >= 'A' && c <= 'Z') ? (c | 0x20) : c)
#define ngx_toupper(c)      (u_char) ((c >= 'a' && c <= 'z') ? (c & ~0x20) : c)

Redis源码中转换字符大小写

/* Apply tolower() to every character of the sds string 's'. */
void sdstolower(sds s) { 
    int len = sdslen(s), j;

    //调用C的库函数
    for (j = 0; j < len; j++) s[j] = tolower(s[j]);
}

/* Apply toupper() to every character of the sds string 's'. */
void sdstoupper(sds s) { 
    int len = sdslen(s), j;

    for (j = 0; j < len; j++) s[j] = toupper(s[j]);
}

PHP源码中转换字符大小写 (strtolower，strtoupper函数具体实现)

PHPAPI char *php_strtolower(char *s, size_t len)
{
    unsigned char *c, *e;

    c = (unsigned char *)s;
    e = c+len;

    while (c < e) {
        *c = tolower(*c);
        c++;
    }
    return s;
}

PHPAPI char *php_strtoupper(char *s, size_t len)
{
    unsigned char *c, *e;

    c = (unsigned char *)s;
    e = (unsigned char *)c+len;
    
    while (c < e) {
        *c = toupper(*c);
        c++; 
    }   
    return s;
}