foundationdb/contrib/libb64/cdecode.c

83 lines
2.6 KiB
C

/*
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 "libb64/cdecode.h"
int base64_decode_value(int value_in) {
static const int 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 int decoding_size = sizeof(decoding) / sizeof(decoding[0]);
value_in -= 43;
if (value_in < 0 || value_in >= decoding_size)
return -1;
return decoding[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;
int fragment = 0;
*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 = base64_decode_value(*codechar++);
} while (fragment < 0);
*plainchar = (char)((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 = base64_decode_value(*codechar++);
} while (fragment < 0);
*plainchar++ |= (char)((fragment & 0x030) >> 4);
*plainchar = (char)((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 = base64_decode_value(*codechar++);
} while (fragment < 0);
*plainchar++ |= (char)((fragment & 0x03c) >> 2);
*plainchar = (char)((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 = base64_decode_value(*codechar++);
} while (fragment < 0);
*plainchar++ |= (char)((fragment & 0x03f));
}
}
/* control should not reach here */
return plainchar - plaintext_out;
}