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/*
* Copyright 2011-2013 Blender Foundation
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/* TODO(sergey): Consider moving portable ctz/clz stuff to util. */
CCL_NAMESPACE_BEGIN
/* "Correlated Multi-Jittered Sampling"
* Andrew Kensler, Pixar Technical Memo 13-01, 2013 */
/* todo: find good value, suggested 64 gives pattern on cornell box ceiling */
#define CMJ_RANDOM_OFFSET_LIMIT 4096
ccl_device_inline bool cmj_is_pow2(int i)
{
return (i & (i - 1)) == 0;
}
ccl_device_inline int cmj_fast_mod_pow2(int a, int b)
{
return (a & (b - 1));
}
/* a must be > 0 and b must be > 1 */
ccl_device_inline int cmj_fast_div_pow2(int a, int b)
{
kernel_assert(a > 0);
kernel_assert(b > 1);
#if defined(__KERNEL_SSE2__)
# ifdef _MSC_VER
unsigned long ctz;
_BitScanForward(&ctz, b);
return a >> ctz;
# else
return a >> __builtin_ctz(b);
# endif
#elif defined(__KERNEL_CUDA__)
return a >> (__ffs(b) - 1);
#else
return a/b;
#endif
}
ccl_device_inline uint cmj_w_mask(uint w)
{
kernel_assert(w > 1);
#if defined(__KERNEL_SSE2__)
# ifdef _MSC_VER
unsigned long leading_zero;
_BitScanReverse(&leading_zero, w);
return ((1 << (1 + leading_zero)) - 1);
# else
return ((1 << (32 - __builtin_clz(w))) - 1);
# endif
#elif defined(__KERNEL_CUDA__)
return ((1 << (32 - __clz(w))) - 1);
#else
w |= w >> 1;
w |= w >> 2;
w |= w >> 4;
w |= w >> 8;
w |= w >> 16;
return w;
#endif
}
ccl_device_inline uint cmj_permute(uint i, uint l, uint p)
{
uint w = l - 1;
if((l & w) == 0) {
/* l is a power of two (fast) */
i ^= p;
i *= 0xe170893d;
i ^= p >> 16;
i ^= (i & w) >> 4;
i ^= p >> 8;
i *= 0x0929eb3f;
i ^= p >> 23;
i ^= (i & w) >> 1;
i *= 1 | p >> 27;
i *= 0x6935fa69;
i ^= (i & w) >> 11;
i *= 0x74dcb303;
i ^= (i & w) >> 2;
i *= 0x9e501cc3;
i ^= (i & w) >> 2;
i *= 0xc860a3df;
i &= w;
i ^= i >> 5;
return (i + p) & w;
}
else {
/* l is not a power of two (slow) */
w = cmj_w_mask(w);
do {
i ^= p;
i *= 0xe170893d;
i ^= p >> 16;
i ^= (i & w) >> 4;
i ^= p >> 8;
i *= 0x0929eb3f;
i ^= p >> 23;
i ^= (i & w) >> 1;
i *= 1 | p >> 27;
i *= 0x6935fa69;
i ^= (i & w) >> 11;
i *= 0x74dcb303;
i ^= (i & w) >> 2;
i *= 0x9e501cc3;
i ^= (i & w) >> 2;
i *= 0xc860a3df;
i &= w;
i ^= i >> 5;
} while(i >= l);
return (i + p) % l;
}
}
ccl_device_inline uint cmj_hash(uint i, uint p)
{
i ^= p;
i ^= i >> 17;
i ^= i >> 10;
i *= 0xb36534e5;
i ^= i >> 12;
i ^= i >> 21;
i *= 0x93fc4795;
i ^= 0xdf6e307f;
i ^= i >> 17;
i *= 1 | p >> 18;
return i;
}
ccl_device_inline float cmj_randfloat(uint i, uint p)
{
return cmj_hash(i, p) * (1.0f / 4294967808.0f);
}
#ifdef __CMJ__
ccl_device float cmj_sample_1D(int s, int N, int p)
{
kernel_assert(s < N);
uint x = cmj_permute(s, N, p * 0x68bc21eb);
float jx = cmj_randfloat(s, p * 0x967a889b);
float invN = 1.0f/N;
return (x + jx)*invN;
}
ccl_device void cmj_sample_2D(int s, int N, int p, float *fx, float *fy)
{
kernel_assert(s < N);
#if defined(__KERNEL_CUDA__)
int m = float_to_int(__fsqrt_ru(N));
#else
int m = float_to_int(sqrtf(N));
#endif
int n = (N + m - 1)/m;
float invN = 1.0f/N;
float invm = 1.0f/m;
float invn = 1.0f/n;
s = cmj_permute(s, N, p * 0x51633e2d);
int sdivm, smodm;
if(cmj_is_pow2(m)) {
sdivm = cmj_fast_div_pow2(s, m);
smodm = cmj_fast_mod_pow2(s, m);
}
else {
/* Doing s*inmv gives precision issues here. */
sdivm = s / m;
smodm = s - sdivm*m;
}
uint sx = cmj_permute(smodm, m, p * 0x68bc21eb);
uint sy = cmj_permute(sdivm, n, p * 0x02e5be93);
float jx = cmj_randfloat(s, p * 0x967a889b);
float jy = cmj_randfloat(s, p * 0x368cc8b7);
*fx = (sx + (sy + jx)*invn)*invm;
*fy = (s + jy)*invN;
}
#endif
CCL_NAMESPACE_END
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