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Fixed random lfsr generation in pokey.c. This fixes MT00501 while tempest is still starting up. [Couriersud]

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Couriersud 2012-05-18 22:02:51 +00:00
parent d211dd4ec3
commit 94a28f7834
1 changed files with 42 additions and 2 deletions
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44
src/emu/sound/pokey.c
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@ -89,7 +89,7 @@
#define VERBOSE_SOUND 0
#define VERBOSE_TIMER 0
#define VERBOSE_POLY 0
#define VERBOSE_RAND 0
#define VERBOSE_RAND 1
#define LOG(x) do { if (VERBOSE) logerror x; } while (0)
@ -419,6 +419,46 @@ static void poly_init(UINT8 *poly, int size, int left, int right, int add)
}
static void rand_init(UINT8 *rng, int size, int left, int right, int add)
{
int mask = (1 << size) - 1;
int i;
UINT32 lfsr = 0;
LOG_RAND(("rand %d\n", size));
if (size == 17)
{
for( i = 0; i < mask; i++ )
{
/* calculate next bit @ 7 */
int in8 = !((lfsr >> 8) & 1) ^ ((lfsr >> 13) & 1);
int in = (lfsr & 1);
lfsr = lfsr >> 1;
lfsr = (lfsr & 0xff7f) | (in8 << 7);
lfsr = (in << 16) | lfsr;
*rng = (lfsr >> 8) & 0xff; /* use bits 0..7 */
LOG_RAND(("%05x: %02x\n", lfsr, *rng));
rng++;
}
}
else
{
for( i = 0; i < mask; i++ )
{
/* calculate next bit */
int in = !((lfsr >> 0) & 1) ^ ((lfsr >> 5) & 1);
lfsr = lfsr >> 1;
lfsr = (in << 8) | lfsr;
*rng = lfsr & 0xff; /* use bits 0..7 */
LOG_RAND(("%05x: %02x\n", lfsr, *rng));
rng++;
}
}
}
#if 0
static void rand_init_old(UINT8 *rng, int size, int left, int right, int add)
{
int mask = (1 << size) - 1;
int i, x = 0;
@ -436,7 +476,7 @@ static void rand_init(UINT8 *rng, int size, int left, int right, int add)
x = ((x << left) + (x >> right) + add) & mask;
}
}
#endif
static void register_for_save(pokey_state *chip, device_t *device)
{