src/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 "cdecode.h"
   9 #include "utils.h"
  10
  11 _hidden int base64_decode_value(char value_in)
  12 {
  13         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};
  14         static const char decoding_size = sizeof(decoding);
  15         value_in -= 43;
  16         if (value_in < 0 || value_in > decoding_size) return -1;
  17         return decoding[(int)value_in];
  18 }
  19
  20 void base64_init_decodestate(base64_decodestate* state_in)
  21 {
  22         state_in->step = step_a;
  23         state_in->plainchar = 0;
  24 }
  25
  26 _hidden int base64_decode_block(const char* code_in, const int length_in,
  27         char* plaintext_out, base64_decodestate* state_in)
  28 {
  29         const char* codechar = code_in;
  30         char* plainchar = plaintext_out;
  31         char fragment;
  32
  33         *plainchar = state_in->plainchar;
  34
  35         switch (state_in->step)
  36         {
  37                 while (1)
  38                 {
  39         case step_a:
  40                         do {
  41                                 if (codechar == code_in+length_in)
  42                                 {
  43                                         state_in->step = step_a;
  44                                         state_in->plainchar = *plainchar;
  45                                         return plainchar - plaintext_out;
  46                                 }
  47                                 fragment = (char)base64_decode_value(*codechar++);
  48                         } while (fragment < 0);
  49                         *plainchar    = (fragment & 0x03f) << 2;
  50         case step_b:
  51                         do {
  52                                 if (codechar == code_in+length_in)
  53                                 {
  54                                         state_in->step = step_b;
  55                                         state_in->plainchar = *plainchar;
  56                                         return plainchar - plaintext_out;
  57                                 }
  58                                 fragment = (char)base64_decode_value(*codechar++);
  59                         } while (fragment < 0);
  60                         *plainchar++ |= (fragment & 0x030) >> 4;
  61                         *plainchar    = (fragment & 0x00f) << 4;
  62         case step_c:
  63                         do {
  64                                 if (codechar == code_in+length_in)
  65                                 {
  66                                         state_in->step = step_c;
  67                                         state_in->plainchar = *plainchar;
  68                                         return plainchar - plaintext_out;
  69                                 }
  70                                 fragment = (char)base64_decode_value(*codechar++);
  71                         } while (fragment < 0);
  72                         *plainchar++ |= (fragment & 0x03c) >> 2;
  73                         *plainchar    = (fragment & 0x003) << 6;
  74         case step_d:
  75                         do {
  76                                 if (codechar == code_in+length_in)
  77                                 {
  78                                         state_in->step = step_d;
  79                                         state_in->plainchar = *plainchar;
  80                                         return plainchar - plaintext_out;
  81                                 }
  82                                 fragment = (char)base64_decode_value(*codechar++);
  83                         } while (fragment < 0);
  84                         *plainchar++   |= (fragment & 0x03f);
  85                 }
  86         }
  87         /* control should not reach here */
  88         return plainchar - plaintext_out;
  89 }