base64编解码实现

Posted 2020-08-11 chencesc

#include <stdio.h>
#include <stdlib.h>
#include <limits.h>
#include <string.h>
#include <stdint.h>

int Base64Decode(const char *in, char* out, int out_length)
{
    int i, v;

    static const uint8_t decodeMap[] =
    {   
        0x3e, 0xff, 0xff, 0xff, 0x3f, 0x34, 0x35, 0x36,
        0x37, 0x38, 0x39, 0x3a, 0x3b, 0x3c, 0x3d, 0xff,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x00, 0x01,
        0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09,
        0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f, 0x10, 0x11,
        0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x1a, 0x1b,
        0x1c, 0x1d, 0x1e, 0x1f, 0x20, 0x21, 0x22, 0x23,
        0x24, 0x25, 0x26, 0x27, 0x28, 0x29, 0x2a, 0x2b,
        0x2c, 0x2d, 0x2e, 0x2f, 0x30, 0x31, 0x32, 0x33
    };  

    char *dst = out;

    v = 0;
    for (i = 0; in[i] && in[i] != ‘=‘; i++) {
        unsigned int index= in[i]-43;
        if (index>=80 || decodeMap[index] == 0xff)
            return -1; 
        v = (v << 6) + decodeMap[index];
        if (i & 3) {
            if (dst - out < out_length) {
                *dst++ = v >> (6 - 2 * (i & 3));
            }
        }
    }