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 static int8_t base64_decode_value(int8_t value_in) {
  12         static const int8_t decoding[] = {
  13         62, -1, -1, -1, 63, 52, 53, 54,
  14         55, 56, 57, 58, 59, 60, 61, -1,
  15         -1, -1, -2, -1, -1, -1,  0,  1,
  16          2,  3,  4,  5,  6,  7,  8,  9,
  17         10, 11, 12, 13, 14, 15, 16, 17,
  18         18, 19, 20, 21, 22, 23, 24, 25,
  19         -1, -1, -1, -1, -1, -1, 26, 27,
  20         28, 29, 30, 31, 32, 33, 34, 35,
  21         36, 37, 38, 39, 40, 41, 42, 43,
  22         44, 45, 46, 47, 48, 49, 50, 51 };
  23     /* The value is 80, so it fits into int8_t. */
  24         static const int8_t decoding_size = sizeof(decoding)/sizeof(*decoding);
  25         value_in -= 43;
  26         if (value_in < 0 || value_in >= decoding_size) return -1;
  27         return decoding[value_in];
  28 }
  29
  30
  31 _hidden void _isds_base64_init_decodestate(base64_decodestate *state_in) {
  32         state_in->step = step_a;
  33         state_in->plainchar = 0;
  34 }
  35
  36
  37 _hidden size_t _isds_base64_decode_block(const int8_t *code_in,
  38         const size_t length_in, int8_t *plaintext_out,
  39         base64_decodestate *state_in) {
  40         const int8_t *codechar = code_in;
  41         int8_t *plainchar = plaintext_out;
  42         int8_t fragment;
  43
  44         *plainchar = state_in->plainchar;
  45
  46         switch (state_in->step) {
  47                 while (1) {
  48         case step_a:
  49                         do {
  50                                 if (codechar == code_in + length_in) {
  51                                         state_in->step = step_a;
  52                                         state_in->plainchar = *plainchar;
  53                                         return plainchar - plaintext_out;
  54                                 }
  55                                 fragment = base64_decode_value(*codechar++);
  56                         } while (fragment < 0);
  57                         *plainchar   = (fragment & 0x03f) << 2;
  58         case step_b:
  59                         do {
  60                                 if (codechar == code_in+length_in) {
  61                                         state_in->step = step_b;
  62                                         state_in->plainchar = *plainchar;
  63                                         return plainchar - plaintext_out;
  64                                 }
  65                                 fragment = base64_decode_value(*codechar++);
  66                         } while (fragment < 0);
  67                         *plainchar++ |= (fragment & 0x030) >> 4;
  68                         *plainchar    = (fragment & 0x00f) << 4;
  69         case step_c:
  70                         do {
  71                                 if (codechar == code_in+length_in) {
  72                                         state_in->step = step_c;
  73                                         state_in->plainchar = *plainchar;
  74                                         return plainchar - plaintext_out;
  75                                 }
  76                                 fragment = base64_decode_value(*codechar++);
  77                         } while (fragment < 0);
  78                         *plainchar++ |= (fragment & 0x03c) >> 2;
  79                         *plainchar    = (fragment & 0x003) << 6;
  80         case step_d:
  81                         do {
  82                                 if (codechar == code_in+length_in) {
  83                                         state_in->step = step_d;
  84                                         state_in->plainchar = *plainchar;
  85                                         return plainchar - plaintext_out;
  86                                 }
  87                                 fragment = base64_decode_value(*codechar++);
  88                         } while (fragment < 0);
  89                         *plainchar++   |= (fragment & 0x03f);
  90                 } /* while */
  91         } /* switch */
  92
  93         /* control should not reach here */
  94         return plainchar - plaintext_out;
  95 }