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Probably fixed instability of single-precision floating-point RNG

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This commit is contained in:
Andrey Kamaev 2012-04-18 06:09:31 +00:00
parent 4ec74414bb
commit 0fd5a9e965
1 changed files with 40 additions and 14 deletions
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54
modules/core/src/rand.cpp
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@ -48,6 +48,10 @@
#include "precomp.hpp"
#if defined __SSE2__ || (defined _M_IX86_FP && 2 == _M_IX86_FP)
#include "emmintrin.h"
#endif
namespace cv
{
@ -196,33 +200,55 @@ DEF_RANDI_FUNC(8s, schar)
DEF_RANDI_FUNC(16u, ushort)
DEF_RANDI_FUNC(16s, short)
DEF_RANDI_FUNC(32s, int)
static void randf_32f( float* arr, int len, uint64* state, const Vec2f* p, bool )
{
uint64 temp = *state;
int i;
int i = 0;
for( i = 0; i <= len - 4; i += 4 )
for( ; i <= len - 4; i += 4 )
{
float f0, f1;
float f[4];
f[0] = (float)(int)(temp = RNG_NEXT(temp));
f[1] = (float)(int)(temp = RNG_NEXT(temp));
f[2] = (float)(int)(temp = RNG_NEXT(temp));
f[3] = (float)(int)(temp = RNG_NEXT(temp));
temp = RNG_NEXT(temp);
f0 = (int)temp*p[i][0] + p[i][1];
temp = RNG_NEXT(temp);
f1 = (int)temp*p[i+1][0] + p[i+1][1];
arr[i] = f0; arr[i+1] = f1;
// handwritten SSE is required not for performance but for numerical stability!
// both 32-bit gcc and MSVC compilers trend to generate double precision SSE
// while 64-bit compilers generate single precision SIMD instructions
// so manual vectorisation forces all compilers to the single precision
#if defined __SSE2__ || (defined _M_IX86_FP && 2 == _M_IX86_FP)
__m128 q0 = _mm_loadu_ps((const float*)(p + i));
__m128 q1 = _mm_loadu_ps((const float*)(p + i + 2));
temp = RNG_NEXT(temp);
f0 = (int)temp*p[i+2][0] + p[i+2][1];
temp = RNG_NEXT(temp);
f1 = (int)temp*p[i+3][0] + p[i+3][1];
arr[i+2] = f0; arr[i+3] = f1;
__m128 q01l = _mm_unpacklo_ps(q0, q1);
__m128 q01h = _mm_unpackhi_ps(q0, q1);
__m128 p0 = _mm_unpacklo_ps(q01l, q01h);
__m128 p1 = _mm_unpackhi_ps(q01l, q01h);
_mm_storeu_ps(arr + i, _mm_add_ps(_mm_mul_ps(_mm_loadu_ps(f), p0), p1));
#else
arr[i+0] = f[0]*p[i+0][0] + p[i+0][1];
arr[i+1] = f[1]*p[i+1][0] + p[i+1][1];
arr[i+2] = f[2]*p[i+2][0] + p[i+2][1];
arr[i+3] = f[3]*p[i+3][0] + p[i+3][1];
#endif
}
for( ; i < len; i++ )
{
temp = RNG_NEXT(temp);
arr[i] = (int)temp*p[i][0] + p[i][1];
#if defined __SSE2__ || (defined _M_IX86_FP && 2 == _M_IX86_FP)
_mm_store_ss(arr + i, _mm_add_ss(
_mm_mul_ss(_mm_set_ss((float)(int)temp), _mm_set_ss(p[i][0])),
_mm_set_ss(p[i][1]))
);
#else
arr[i] += (int)temp*p[i][0] + p[i][1];
#endif
}
*state = temp;