base64_to.c

   1 #include <stddef.h>
   2 #include <stdint.h>
   3 #include "types.h"
   4 #include "base64.h"
   5
   6 static const char base64t[64] = {
   7         'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H',
   8         'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',
   9         'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X',
  10         'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f',
  11         'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n',
  12         'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
  13         'w', 'x', 'y', 'z', '0', '1', '2', '3',
  14         '4', '5', '6', '7', '8', '9', '+', '/',
  15 };
  16
  17 char *base64_to(char *dst,const u8 *src,size_t slen)
  18 {
  19         if (!slen) {
  20                 *dst = '\0';
  21                 return dst;
  22         }
  23
  24         for(size_t i = 0; i < slen;) {
  25                 u32 threebytes = 0;
  26                 threebytes |= (i < slen ? (unsigned char)src[i++] : (unsigned char)0) << (2 * 8);
  27                 threebytes |= (i < slen ? (unsigned char)src[i++] : (unsigned char)0) << (1 * 8);
  28                 threebytes |= (i < slen ? (unsigned char)src[i++] : (unsigned char)0) << (0 * 8);
  29
  30                 *dst++ = base64t[(threebytes >> (3 * 6)) & 63];
  31                 *dst++ = base64t[(threebytes >> (2 * 6)) & 63];
  32                 *dst++ = base64t[(threebytes >> (1 * 6)) & 63];
  33                 *dst++ = base64t[(threebytes >> (0 * 6)) & 63];
  34         }
  35
  36         switch (slen % 3) {
  37                 case 0 : break;
  38                 case 1 : {
  39                         *(dst-2) = '=';
  40                         *(dst-1) = '=';
  41                         break;
  42                 }
  43                 case 2 : {
  44                         *(dst-1) = '=';
  45                         break;
  46                 }
  47         }
  48
  49         *dst = '\0';
  50         return dst;
  51 }