libcitadel/lib/b64/cdecode.c

   1 /*
   2 cdecoder.c - c source to a base64 decoding algorithm implementation
   3
   4 This is part of the libb64 project, and has been placed in the public domain.
   5 For details, see http://sourceforge.net/projects/libb64
   6 */
   7
   8 #include "b64/cdecode.h"
   9
  10 int base64_decode_value(char value_in)
  11 {
  12         static const char decoding[] = {62,-1,-1,-1,63,52,53,54,55,56,57,58,59,60,61,-1,-1,-1,-2,-1,-1,-1,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,-1,-1,-1,-1,-1,-1,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51};
  13         static const char decoding_size = sizeof(decoding);
  14         value_in -= 43;
  15         if (value_in < 0 || value_in > decoding_size) return -1;
  16         return decoding[(int)value_in];
  17 }
  18
  19 void base64_init_decodestate(base64_decodestate* state_in)
  20 {
  21         state_in->step = step_a;
  22         state_in->plainchar = 0;
  23 }
  24
  25 int base64_decode_block(const char* code_in, const int length_in, char* plaintext_out, base64_decodestate* state_in)
  26 {
  27         const char* codechar = code_in;
  28         char* plainchar = plaintext_out;
  29         char fragment;
  30
  31         *plainchar = state_in->plainchar;
  32
  33         switch (state_in->step)
  34         {
  35                 while (1)
  36                 {
  37         case step_a:
  38                         do {
  39                                 if (codechar == code_in+length_in)
  40                                 {
  41                                         state_in->step = step_a;
  42                                         state_in->plainchar = *plainchar;
  43                                         return plainchar - plaintext_out;
  44                                 }
  45                                 fragment = (char)base64_decode_value(*codechar++);
  46                         } while (fragment < 0);
  47                         *plainchar    = (fragment & 0x03f) << 2;
  48         case step_b:
  49                         do {
  50                                 if (codechar == code_in+length_in)
  51                                 {
  52                                         state_in->step = step_b;
  53                                         state_in->plainchar = *plainchar;
  54                                         return plainchar - plaintext_out;
  55                                 }
  56                                 fragment = (char)base64_decode_value(*codechar++);
  57                         } while (fragment < 0);
  58                         *plainchar++ |= (fragment & 0x030) >> 4;
  59                         *plainchar    = (fragment & 0x00f) << 4;
  60         case step_c:
  61                         do {
  62                                 if (codechar == code_in+length_in)
  63                                 {
  64                                         state_in->step = step_c;
  65                                         state_in->plainchar = *plainchar;
  66                                         return plainchar - plaintext_out;
  67                                 }
  68                                 fragment = (char)base64_decode_value(*codechar++);
  69                         } while (fragment < 0);
  70                         *plainchar++ |= (fragment & 0x03c) >> 2;
  71                         *plainchar    = (fragment & 0x003) << 6;
  72         case step_d:
  73                         do {
  74                                 if (codechar == code_in+length_in)
  75                                 {
  76                                         state_in->step = step_d;
  77                                         state_in->plainchar = *plainchar;
  78                                         return plainchar - plaintext_out;
  79                                 }
  80                                 fragment = (char)base64_decode_value(*codechar++);
  81                         } while (fragment < 0);
  82                         *plainchar++   |= (fragment & 0x03f);
  83                 }
  84         }
  85         /* control should not reach here */
  86         return plainchar - plaintext_out;
  87 }
  88