base64编解码--C语言实现

最近项目需要在传输数据的时候进行base64编码传输，在此记录一下实现过程
下边是具体的实现源码

static const char *ALPHA_BASE = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
 
char *encode(const char *buf, const long size, char *base64Char) {
    int a = 0;
    int i = 0;
    while (i < size) {
        char b0 = buf[i++];
        char b1 = (i < size) ? buf[i++] : 0;
        char b2 = (i < size) ? buf[i++] : 0;
         
        int int63 = 0x3F; //  00111111
        int int255 = 0xFF; // 11111111
        base64Char[a++] = ALPHA_BASE[(b0 >> 2) & int63];
        base64Char[a++] = ALPHA_BASE[((b0 << 4) | ((b1 & int255) >> 4)) & int63];
        base64Char[a++] = ALPHA_BASE[((b1 << 2) | ((b2 & int255) >> 6)) & int63];
        base64Char[a++] = ALPHA_BASE[b2 & int63];
    }
    switch (size % 3) {
        case 1:
            base64Char[--a] = '=';
        case 2:
            base64Char[--a] = '=';
    }
    return base64Char;
}
 
char *decode(const char *base64Char, const long base64CharSize, char *originChar, long originCharSize) {
    int toInt[128] = {-1};
    for (int i = 0; i < 64; i++) {
        toInt[ALPHA_BASE[i]] = i;
    }
    int int255 = 0xFF;
    int index = 0;
    for (int i = 0; i < base64CharSize; i += 4) {
        int c0 = toInt[base64Char[i]];
        int c1 = toInt[base64Char[i + 1]];
        originChar[index++] = (((c0 << 2) | (c1 >> 4)) & int255);
        if (index >= originCharSize) {
            return originChar;
        }
        int c2 = toInt[base64Char[i + 2]];
        originChar[index++] = (((c1 << 4) | (c2 >> 2)) & int255);
        if (index >= originCharSize) {
            return originChar;
        }
        int c3 = toInt[base64Char[i + 3]];
        originChar[index++] = (((c2 << 6) | c3) & int255);
    }
    return originChar;
}