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_decode.h"
9
base64_decode_value(char value_in)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
base64_init_decodestate(base64_decodestate * state_in)19 void base64_init_decodestate(base64_decodestate* state_in)
20 {
21 state_in->step = step_a;
22 state_in->plainchar = 0;
23 }
24
base64_decode_block(const char * code_in,const int length_in,char * plaintext_out,base64_decodestate * state_in)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