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/*Written by Timothy B. Terriberry (tterribe@xiph.org) 1999-2009 public domain.
Based on the public domain implementation by Robert J. Jenkins Jr.*/
#include "isaac.h"
#include <float.h>
#include <math.h>
#include <string.h>
#define ISAAC_MASK (0xFFFFFFFFU)
static void isaac_update(isaac_ctx *_ctx)
{
unsigned *m;
unsigned *r;
unsigned a;
unsigned b;
unsigned x;
unsigned y;
int i;
m = _ctx->m;
r = _ctx->r;
a = _ctx->a;
b = _ctx->b + (++_ctx->c) & ISAAC_MASK;
for (i = 0; i < ISAAC_SZ / 2; i++) {
x = m[i];
a = (a ^ a << 13) + m[i + ISAAC_SZ / 2] & ISAAC_MASK;
m[i] = y = m[(x & ISAAC_SZ - 1 << 2) >> 2] + a + b & ISAAC_MASK;
r[i] = b = m[y >> ISAAC_SZ_LOG + 2 & ISAAC_SZ - 1] + x & ISAAC_MASK;
x = m[++i];
a = (a ^ a >> 6) + m[i + ISAAC_SZ / 2] & ISAAC_MASK;
m[i] = y = m[(x & ISAAC_SZ - 1 << 2) >> 2] + a + b & ISAAC_MASK;
r[i] = b = m[y >> ISAAC_SZ_LOG + 2 & ISAAC_SZ - 1] + x & ISAAC_MASK;
x = m[++i];
a = (a ^ a << 2) + m[i + ISAAC_SZ / 2] & ISAAC_MASK;
m[i] = y = m[(x & ISAAC_SZ - 1 << 2) >> 2] + a + b & ISAAC_MASK;
r[i] = b = m[y >> ISAAC_SZ_LOG + 2 & ISAAC_SZ - 1] + x & ISAAC_MASK;
x = m[++i];
a = (a ^ a >> 16) + m[i + ISAAC_SZ / 2] & ISAAC_MASK;
m[i] = y = m[(x & ISAAC_SZ - 1 << 2) >> 2] + a + b & ISAAC_MASK;
r[i] = b = m[y >> ISAAC_SZ_LOG + 2 & ISAAC_SZ - 1] + x & ISAAC_MASK;
}
for (i = ISAAC_SZ / 2; i < ISAAC_SZ; i++) {
x = m[i];
a = (a ^ a << 13) + m[i - ISAAC_SZ / 2] & ISAAC_MASK;
m[i] = y = m[(x & ISAAC_SZ - 1 << 2) >> 2] + a + b & ISAAC_MASK;
r[i] = b = m[y >> ISAAC_SZ_LOG + 2 & ISAAC_SZ - 1] + x & ISAAC_MASK;
x = m[++i];
a = (a ^ a >> 6) + m[i - ISAAC_SZ / 2] & ISAAC_MASK;
m[i] = y = m[(x & ISAAC_SZ - 1 << 2) >> 2] + a + b & ISAAC_MASK;
r[i] = b = m[y >> ISAAC_SZ_LOG + 2 & ISAAC_SZ - 1] + x & ISAAC_MASK;
x = m[++i];
a = (a ^ a << 2) + m[i - ISAAC_SZ / 2] & ISAAC_MASK;
m[i] = y = m[(x & ISAAC_SZ - 1 << 2) >> 2] + a + b & ISAAC_MASK;
r[i] = b = m[y >> ISAAC_SZ_LOG + 2 & ISAAC_SZ - 1] + x & ISAAC_MASK;
x = m[++i];
a = (a ^ a >> 16) + m[i - ISAAC_SZ / 2] & ISAAC_MASK;
m[i] = y = m[(x & ISAAC_SZ - 1 << 2) >> 2] + a + b & ISAAC_MASK;
r[i] = b = m[y >> ISAAC_SZ_LOG + 2 & ISAAC_SZ - 1] + x & ISAAC_MASK;
}
_ctx->b = b;
_ctx->a = a;
_ctx->n = ISAAC_SZ;
}
static void isaac_mix(unsigned _x[8])
{
static const unsigned char SHIFT[8] = { 11, 2, 8, 16, 10, 4, 8, 9 };
int i;
for (i = 0; i < 8; i++) {
_x[i] ^= _x[i + 1 & 7] << SHIFT[i];
_x[i + 3 & 7] += _x[i];
_x[i + 1 & 7] += _x[i + 2 & 7];
i++;
_x[i] ^= _x[i + 1 & 7] >> SHIFT[i];
_x[i + 3 & 7] += _x[i];
_x[i + 1 & 7] += _x[i + 2 & 7];
}
}
void isaac_init(isaac_ctx *_ctx, const void *_seed, int _nseed)
{
const unsigned char *seed;
unsigned *m;
unsigned *r;
unsigned x[8];
int i;
int j;
_ctx->a = _ctx->b = _ctx->c = 0;
m = _ctx->m;
r = _ctx->r;
x[0] = x[1] = x[2] = x[3] = x[4] = x[5] = x[6] = x[7] = 0x9E3779B9;
for (i = 0; i < 4; i++)
isaac_mix(x);
if (_nseed > ISAAC_SEED_SZ_MAX)
_nseed = ISAAC_SEED_SZ_MAX;
seed = (const unsigned char *)_seed;
for (i = 0; i < (_nseed >> 2); i++) {
r[i] = seed[i << 2 | 3] << 24 | seed[i << 2 | 2] << 16 |
seed[i << 2 | 1] << 8 | seed[i << 2];
}
if (_nseed & 3) {
r[i] = seed[i << 2];
for (j = 1; j < (_nseed & 3); j++)
r[i] += seed[i << 2 | j] << (j << 3);
i++;
}
memset(r + i, 0, (ISAAC_SZ - i) * sizeof(*r));
for (i = 0; i < ISAAC_SZ; i += 8) {
for (j = 0; j < 8; j++)
x[j] += r[i + j];
isaac_mix(x);
memcpy(m + i, x, sizeof(x));
}
for (i = 0; i < ISAAC_SZ; i += 8) {
for (j = 0; j < 8; j++)
x[j] += m[i + j];
isaac_mix(x);
memcpy(m + i, x, sizeof(x));
}
isaac_update(_ctx);
}
unsigned isaac_next_uint32(isaac_ctx *_ctx)
{
if (!_ctx->n)
isaac_update(_ctx);
return _ctx->r[--_ctx->n];
}
/*Returns a uniform random integer less than the given maximum value.
_n: The upper bound on the range of numbers returned (not inclusive).
This must be strictly less than 2**32.
Return: An integer uniformly distributed between 0 (inclusive) and _n
(exclusive).*/
unsigned isaac_next_uint(isaac_ctx *_ctx, unsigned _n)
{
unsigned r;
unsigned v;
unsigned d;
do {
r = isaac_next_uint32(_ctx);
v = r % _n;
d = r - v;
} while ((d + _n - 1 & ISAAC_MASK) < d);
return v;
}
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