95 lines
3.3 KiB
C
95 lines
3.3 KiB
C
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/*
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cdecoder.c - c source to a base64 decoding algorithm implementation
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This is part of the libb64 project, and has been placed in the public domain.
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For details, see http://sourceforge.net/projects/libb64
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*/
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#include "cdecode.h"
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int base64_decode_value(char value_in)
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{
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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};
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static const char decoding_size = sizeof(decoding);
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value_in -= 43;
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if (value_in < 0 || value_in > decoding_size) {
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return -1;
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}
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return decoding[(int)value_in];
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}
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void base64_init_decodestate(base64_decodestate* state_in)
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{
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state_in->step = step_a;
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state_in->plainchar = 0;
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}
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int base64_decode_block(const char* code_in, const int length_in, char* plaintext_out, base64_decodestate* state_in)
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{
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const char* codechar = code_in;
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char* plainchar = plaintext_out;
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char fragment;
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*plainchar = state_in->plainchar;
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switch (state_in->step) {
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while (1) {
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case step_a:
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do {
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if (codechar == code_in+length_in) {
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state_in->step = step_a;
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state_in->plainchar = *plainchar;
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return plainchar - plaintext_out;
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}
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fragment = (char)base64_decode_value(*codechar++);
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} while (fragment < 0);
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*plainchar = (fragment & 0x03f) << 2;
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case step_b:
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do {
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if (codechar == code_in+length_in) {
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state_in->step = step_b;
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state_in->plainchar = *plainchar;
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return plainchar - plaintext_out;
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}
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fragment = (char)base64_decode_value(*codechar++);
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} while (fragment < 0);
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*plainchar++ |= (fragment & 0x030) >> 4;
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*plainchar = (fragment & 0x00f) << 4;
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case step_c:
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do {
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if (codechar == code_in+length_in) {
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state_in->step = step_c;
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state_in->plainchar = *plainchar;
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return plainchar - plaintext_out;
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}
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fragment = (char)base64_decode_value(*codechar++);
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} while (fragment < 0);
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*plainchar++ |= (fragment & 0x03c) >> 2;
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*plainchar = (fragment & 0x003) << 6;
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case step_d:
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do {
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if (codechar == code_in+length_in) {
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state_in->step = step_d;
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state_in->plainchar = *plainchar;
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return plainchar - plaintext_out;
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}
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fragment = (char)base64_decode_value(*codechar++);
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} while (fragment < 0);
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*plainchar++ |= (fragment & 0x03f);
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}
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}
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/* control should not reach here */
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return plainchar - plaintext_out;
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}
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int base64_decode_chars(const char* code_in, const int length_in, char* plaintext_out)
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{
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base64_decodestate _state;
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base64_init_decodestate(&_state);
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int len = base64_decode_block(code_in, length_in, plaintext_out, &_state);
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if(len > 0) {
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plaintext_out[len] = 0;
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}
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return len;
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}
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