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