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Update seed_rng() in stdlib to take a varying seed.

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Previously, we were trying to take a uniform seed and then shuffle that
around to initialize the state for each of the program instances.  This
was becoming increasingly untenable and brittle.

Now a varying seed is expected and used.
This commit is contained in:
Matt Pharr
2012-05-30 10:35:41 -07:00
parent 5cb53f52c3
commit 8fd9b84a80
6 changed files with 11 additions and 58 deletions
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2
docs/ispc.rst
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@@ -3147,7 +3147,7 @@ library. State for the RNG is maintained in an instance of the
::
struct RNGState;
void seed_rng(varying RNGState * uniform state, uniform int seed)
void seed_rng(varying RNGState * uniform state, int seed)
void seed_rng(uniform RNGState * uniform state, uniform int seed)
After the RNG is seeded, the ``random()`` function can be used to get a

2
examples/aobench/ao.ispc
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@@ -210,7 +210,7 @@ static void ao_scanlines(uniform int y0, uniform int y1, uniform int w,
{ { 1.0f, 0.0f, -2.2f }, 0.5f } };
RNGState rngstate;
seed_rng(&rngstate, y0);
seed_rng(&rngstate, programIndex + (y0 << (programIndex & 15)));
float invSamples = 1.f / nsubsamples;
foreach_tiled(y = y0 ... y1, x = 0 ... w,

2
examples/aobench_instrumented/ao.ispc
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@@ -211,7 +211,7 @@ static void ao_scanlines(uniform int y0, uniform int y1, uniform int w,
{ { 1.0f, 0.0f, -2.2f }, 0.5f } };
RNGState rngstate;
seed_rng(&rngstate, y0);
seed_rng(&rngstate, programIndex + (y0 << (programIndex & 15)));
// Compute the mapping between the 'programCount'-wide program
// instances running in parallel and samples in the image.

59
stdlib.ispc
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@@ -4026,60 +4026,13 @@ static inline uniform float frandom(uniform RNGState * uniform state)
return floatbits(0x3F800000 | irand)-1.0f;
}
static inline uniform unsigned int __seed4(varying RNGState * uniform state,
uniform int start,
uniform unsigned int seed) {
uniform unsigned int c1 = 0xf0f0f0f0;
uniform unsigned int c2 = 0x0f0f0f0f;
state->z1 = insert(state->z1, start + 0, seed);
state->z1 = insert(state->z1, start + 1, seed ^ c1);
state->z1 = insert(state->z1, start + 2, (seed << 3) ^ c1);
state->z1 = insert(state->z1, start + 3, (seed << 2) ^ c2);
seed += 131;
state->z2 = insert(state->z2, start + 0, seed);
state->z2 = insert(state->z2, start + 1, seed ^ c1);
state->z2 = insert(state->z2, start + 2, (seed << 3) ^ c1);
state->z2 = insert(state->z2, start + 3, (seed << 2) ^ c2);
seed ^= extract(state->z2, 2);
state->z3 = insert(state->z3, start + 0, seed);
state->z3 = insert(state->z3, start + 1, seed ^ c1);
state->z3 = insert(state->z3, start + 2, (seed << 3) ^ c1);
state->z3 = insert(state->z3, start + 3, (seed << 2) ^ c2);
seed <<= 4;
seed += 3;
seed ^= extract(state->z1, 3);
state->z4 = insert(state->z4, start + 0, seed);
state->z4 = insert(state->z4, start + 1, seed ^ c1);
state->z4 = insert(state->z4, start + 2, (seed << 3) ^ c1);
state->z4 = insert(state->z4, start + 3, (seed << 2) ^ c2);
return seed;
}
static inline void seed_rng(varying RNGState * uniform state,
uniform unsigned int seed) {
if (programCount == 1) {
state->z1 = seed;
state->z2 = seed ^ 0xbeeff00d;
state->z3 = ((seed & 0xffff) << 16) | (seed >> 16);
state->z4 = (((seed & 0xff) << 24) | ((seed & 0xff00) << 8) |
((seed & 0xff0000) >> 8) | (seed & 0xff000000) >> 24);
}
else {
seed = __seed4(state, 0, seed);
if (programCount == 8)
__seed4(state, 4, seed ^ 0xbeeff00d);
if (programCount == 16) {
__seed4(state, 4, seed ^ 0xbeeff00d);
__seed4(state, 8, ((seed & 0xffff) << 16) | (seed >> 16));
__seed4(state, 12, (((seed & 0xff) << 24) | ((seed & 0xff00) << 8) |
((seed & 0xff0000) >> 8) | (seed & 0xff000000) >> 24));
}
}
unsigned int seed) {
state->z1 = seed;
state->z2 = seed ^ 0xbeeff00d;
state->z3 = ((seed & 0xffff) << 16) | (seed >> 16);
state->z4 = (((seed & 0xff) << 24) | ((seed & 0xff00) << 8) |
((seed & 0xff0000) >> 8) | (seed & 0xff000000) >> 24);
}
static inline void seed_rng(uniform RNGState * uniform state,

2
tests/rand-distrib-1.ispc
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@@ -3,7 +3,7 @@ export uniform int width() { return programCount; }
export void f_fu(uniform float RET[], uniform float aFOO[], uniform float b) {
RNGState state;
seed_rng(&state, 1);
seed_rng(&state, programIndex);
int count[32];
for (uniform int i = 0; i < 32; ++i)
count[i] = (b == 5.) ? 0 : 1;

2
tests/rand-distrib.ispc
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@@ -3,7 +3,7 @@ export uniform int width() { return programCount; }
export void f_f(uniform float RET[], uniform float aFOO[]) {
RNGState state;
seed_rng(&state, 1);
seed_rng(&state, programIndex);
float sum = 0;
uniform int iters = 40000;
for (unsigned int i = 0; i < iters; ++i)