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base64dec.c
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base64dec.c
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/*
* schizo, a set of tools for managing split disk images
* Copyright (C) 2021 Lennert Buytenhek
*
* This library is free software; you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License version
* 2.1 as published by the Free Software Foundation.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Lesser General Public License version 2.1 for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License version 2.1 along with this library; if not, write to the
* Free Software Foundation, Inc., 51 Franklin Street - Fifth Floor,
* Boston, MA 02110-1301, USA.
*/
#include <stdio.h>
#include <stdlib.h>
#include "base64dec.h"
static int base64url_index(char c)
{
if (c >= 'A' && c <= 'Z')
return 0 + (c - 'A');
if (c >= 'a' && c <= 'z')
return 26 + (c - 'a');
if (c >= '0' && c <= '9')
return 52 + (c - '0');
if (c == '-')
return 62;
if (c == '_')
return 63;
return -1;
}
int base64dec(uint8_t *data, const char *b64, int len)
{
int i;
int j;
i = 0;
j = 0;
while (i < len) {
int toread;
int val;
int k;
toread = len - i;
if (toread == 1)
return -1;
if (toread > 4)
toread = 4;
val = 0;
for (k = 0; k < toread; k++) {
int val2;
val2 = base64url_index(b64[i++]);
if (val2 < 0)
return -1;
val |= val2 << (18 - (6 * k));
}
for (k = 1; k < toread; k++) {
data[j++] = (val >> 16) & 0xff;
val <<= 8;
}
}
return 0;
}