83 lines
2.6 KiB
C
83 lines
2.6 KiB
C
/*
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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 "libb64/cdecode.h"
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int base64_decode_value(int value_in) {
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static const int decoding[] = { 62, -1, -1, -1, 63, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -2, -1,
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-1, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17,
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18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1, -1, 26, 27, 28, 29, 30, 31,
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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 int decoding_size = sizeof(decoding) / sizeof(decoding[0]);
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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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return decoding[value_in];
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}
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void base64_init_decodestate(base64_decodestate* state_in) {
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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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const char* codechar = code_in;
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char* plainchar = plaintext_out;
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int fragment = 0;
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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 = base64_decode_value(*codechar++);
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} while (fragment < 0);
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*plainchar = (char)((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 = base64_decode_value(*codechar++);
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} while (fragment < 0);
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*plainchar++ |= (char)((fragment & 0x030) >> 4);
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*plainchar = (char)((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 = base64_decode_value(*codechar++);
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} while (fragment < 0);
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*plainchar++ |= (char)((fragment & 0x03c) >> 2);
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*plainchar = (char)((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 = base64_decode_value(*codechar++);
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} while (fragment < 0);
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*plainchar++ |= (char)((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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