用c语言写的base64编码解码函数！

/* *****************************************************************************

* Description : BASE64 encoding and decoding

* Date : 06-08-21 21:00

* Author : aishen944

* Copryright :

********************************************************************************/

#include <string.h>
#include <stdlib.h>
#include <errno.h>

#define BASE64_PAD64 '='

char base64_alphabet[] = {'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I',
'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R',
'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a',
'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j',
'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's',
't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1',
'2', '3', '4', '5', '6', '7', '8', '9', '+',
'/'};

char base64_suffix_map[256] = {
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 62, 255, 255, 255, 63, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 255, 255,
255, 255, 255, 255, 255, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,
15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 255, 255, 255, 255, 255, 255, 26, 27, 28,
29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48,
49, 50, 51, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255};

static char cmove_bits(unsigned char src, unsigned lnum, unsigned rnum) {
src <<= lnum;
src >>= rnum;
return src;
}

char* base64_encode(const char *data) {
char *ret, *retpos;
int n, m, padnum = 0, retsize, dlen = strlen(data);

if(dlen == 0) return NULL;

/* Account the result buffer size and alloc the memory for it. */
if((dlen % 3) != 0)
padnum = 3 - dlen % 3;
retsize = (dlen + padnum) + ((dlen + padnum) * 1/3) + 1;
if((ret = malloc(retsize)) == NULL)
return NULL;
retpos = ret;

/* Starting to convert the originality characters to BASE64 chracaters.
Converting process keep to 4->6 principle. */
for(m = 0; m < (dlen + padnum); m += 3) {
/* When data is not suffice 24 bits then pad 0 and the empty place pad '='. */
*(retpos) = base64_alphabet[cmove_bits(*data, 0, 2)];
if(m == dlen + padnum - 3 && padnum != 0) { /* Whether the last bits-group suffice 24 bits. */
if(padnum == 1) { /* 16bit need pad one '='. */
*(retpos + 1) = base64_alphabet[cmove_bits(*data, 6, 2) + cmove_bits(*(data + 1), 0, 4)];
*(retpos + 2) = base64_alphabet[cmove_bits(*(data + 1), 4, 2)];
*(retpos + 3) = BASE64_PAD64;
} else if(padnum == 2) { /* 8bit need pad two'='. */
*(retpos + 1) = base64_alphabet[cmove_bits(*data, 6, 2)];
*(retpos + 2) = BASE64_PAD64;
*(retpos + 3) = BASE64_PAD64;
}
} else { /* 24bit normal. */
*(retpos + 1) = base64_alphabet[cmove_bits(*data, 6, 2) + cmove_bits(*(data + 1), 0, 4)];
*(retpos + 2) = base64_alphabet[cmove_bits(*(data + 1), 4, 2) + cmove_bits(*(data + 2), 0, 6)];
*(retpos + 3) = base64_alphabet[*(data + 2) & 0x3f];
}

retpos += 4;
data += 3;
}

ret[retsize - 1] =0;

return ret;
}

char* base64_decode(const char *bdata) {
char *ret = NULL, *retpos;
int n, m, padnum = 0, retsize, bdlen = strlen(bdata);

if(bdlen == 0) return NULL;
if(bdlen % 4 != 0) return NULL;

/* Whether the data have invalid base-64 characters? */
for(m = 0; m < bdlen; ++m) {
if(bdata[m] != BASE64_PAD64 && base64_suffix_map[bdata[m]] == 255)
goto LEND;
}

/* Account the output size. */
if(bdata[bdlen - 1] == '=') padnum = 1;
if(bdata[bdlen - 1] == '=' && bdata[bdlen - 2] == '=') padnum = 2;
retsize = (bdlen - 4) - (bdlen - 4) / 4 + (3 - padnum) + 1;
ret = malloc(retsize);
if(ret == NULL)
return NULL;
retpos = ret;

/* Begging to decode. */
for(m = 0; m < bdlen; m += 4) {
*retpos = cmove_bits(base64_suffix_map[*bdata], 2, 0) + cmove_bits(base64_suffix_map[*(bdata + 1)], 0, 4);
if(m == bdlen - 4 && padnum != 0) { /* Only deal with last four bits. */
if(padnum == 1) /* Have one pad characters, only two availability characters. */
*(retpos + 1) = cmove_bits(base64_suffix_map[*(bdata + 1)], 4, 0) + cmove_bits(base64_suffix_map[*(bdata + 2)], 0, 2);
/*
Have two pad characters, only two availability characters.
if(padnum == 2) {
}
*/
retpos += 3 - padnum;
} else {
*(retpos + 1) = cmove_bits(base64_suffix_map[*(bdata + 1)], 4, 0) + cmove_bits(base64_suffix_map[*(bdata + 2)], 0, 2);
*(retpos + 2) = cmove_bits(base64_suffix_map[*(bdata + 2)], 6, 0) + base64_suffix_map[*(bdata + 3)];
retpos += 3;
}
bdata += 4;
}

ret[retsize - 1] = 0;

LEND: return ret;
}