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/* ScummVM - Graphic Adventure Engine
*
* ScummVM is the legal property of its developers, whose names
* are too numerous to list here. Please refer to the COPYRIGHT
* file distributed with this source distribution.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version 2
* of the License, or (at your option) any later version.
*
* This program 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*
*/
#include "glk/archetype/crypt.h"
#include "glk/archetype/archetype.h"
namespace Glk {
namespace Archetype {
byte CryptMask;
EncryptionType Encryption;
static uint RandSeed;
const int RANDOM_KEY = 33797;
void crypt_init() {
Encryption = NONE;
CryptMask = 0x55;
RandSeed = 0;
}
static void setDecryptionSeed(uint new_seed) {
RandSeed = new_seed;
}
static void cycleRandomSeed() {
uint16 c = RandSeed & 0xffff;
uint val = (uint)c * RANDOM_KEY;
c <<= 3;
c = (c & 0xff) | ((((c >> 8) + c) & 0xff) << 8);
val += (uint)c << 16;
uint16 b = RandSeed >> 16;
val += (uint)b << 16;
b <<= 2;
val += (uint)b << 16;
val += (uint)(b & 0xff) << 24;
b <<= 5;
val += (uint)(b & 0xff) << 24;
RandSeed = val + 1;
}
static uint getDeterministicRandomNumber(uint limit) {
cycleRandomSeed();
return (limit == 0) ? 0 : (RandSeed >> 16) % limit;
}
void cryptinit(EncryptionType crypt_kind, uint seed) {
CryptMask = seed & 0xff;
Encryption = crypt_kind;
if (Encryption == COMPLEX)
setDecryptionSeed(seed);
}
void cryptstr(char *buffer, size_t length) {
byte nextMask;
char *p = buffer;
switch (Encryption) {
case SIMPLE:
for (size_t i = 0; i < length; ++i, ++p)
*p ^= CryptMask;
break;
case PURPLE:
for (size_t i = 0; i < length; ++i, ++p) {
*p ^= CryptMask;
CryptMask += *p & 7;
}
break;
case UNPURPLE:
for (size_t i = 0; i < length; ++i, ++p) {
nextMask = CryptMask + (*p & 7);
*p ^= CryptMask;
CryptMask = nextMask;
}
break;
case COMPLEX:
for (size_t i = 0; i < length; ++i, ++p) {
*p ^= CryptMask;
CryptMask = (byte)getDeterministicRandomNumber(0x100);
}
break;
default:
break;
}
}
} // End of namespace Archetype
} // End of namespace Glk
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