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gallivm: Use a minimax polynomial for exp2 in range [0,1] instead [-0.5,5].

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The advantage of range[-0.5, 0.5] is that it doesn't require floor (for
which intrinsics are only available in SSE4.1).

But the EXP opcode pretty much forces us to use floor, and there is a
good floor approximation around truncation available anyway.

This fixes EXP failures in VShader DCT.
This commit is contained in:
José Fonseca 2010-05-08 21:42:55 +01:00
parent de088c6ae4
commit c376dadbb0
1 changed files with 41 additions and 14 deletions
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55
src/gallium/auxiliary/gallivm/lp_bld_arit.c
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@ -1438,17 +1438,31 @@ lp_build_polynomial(struct lp_build_context *bld,
/**
* Minimax polynomial fit of 2**x, in range [-0.5, 0.5[
* Minimax polynomial fit of 2**x, in range [0, 1[
*/
const double lp_build_exp2_polynomial[] = {
#if EXP_POLY_DEGREE == 5
9.9999994e-1, 6.9315308e-1, 2.4015361e-1, 5.5826318e-2, 8.9893397e-3, 1.8775767e-3
0.999999999690134838155,
0.583974334321735217258,
0.164553105719676828492,
0.0292811063701710962255,
0.00354944426657875141846,
0.000296253726543423377365
#elif EXP_POLY_DEGREE == 4
1.0000026, 6.9300383e-1, 2.4144275e-1, 5.2011464e-2, 1.3534167e-2
1.00000001502262084505,
0.563586057338685991394,
0.150436017652442413623,
0.0243220604213317927308,
0.0025359088446580436489
#elif EXP_POLY_DEGREE == 3
9.9992520e-1, 6.9583356e-1, 2.2606716e-1, 7.8024521e-2
0.999925218562710312959,
0.695833540494823811697,
0.226067155427249155588,
0.0780245226406372992967
#elif EXP_POLY_DEGREE == 2
1.0017247, 6.5763628e-1, 3.3718944e-1
1.00172476321474503578,
0.657636275736077639316,
0.33718943461968720704
#else
#error
#endif
@ -1482,17 +1496,16 @@ lp_build_exp2_approx(struct lp_build_context *bld,
x = lp_build_min(bld, x, lp_build_const_vec(type, 129.0));
x = lp_build_max(bld, x, lp_build_const_vec(type, -126.99999));
/* ipart = int(x - 0.5) */
ipart = LLVMBuildSub(bld->builder, x, lp_build_const_vec(type, 0.5f), "");
ipart = LLVMBuildFPToSI(bld->builder, ipart, int_vec_type, "");
/* ipart = floor(x) */
ipart = lp_build_floor(bld, x);
/* fpart = x - ipart */
fpart = LLVMBuildSIToFP(bld->builder, ipart, vec_type, "");
fpart = LLVMBuildSub(bld->builder, x, fpart, "");
fpart = LLVMBuildSub(bld->builder, x, ipart, "");
}
if(p_exp2_int_part || p_exp2) {
/* expipart = (float) (1 << ipart) */
ipart = LLVMBuildFPToSI(bld->builder, ipart, int_vec_type, "");
expipart = LLVMBuildAdd(bld->builder, ipart, lp_build_const_int_vec(type, 127), "");
expipart = LLVMBuildShl(bld->builder, expipart, lp_build_const_int_vec(type, 23), "");
expipart = LLVMBuildBitCast(bld->builder, expipart, vec_type, "");
@ -1533,13 +1546,27 @@ lp_build_exp2(struct lp_build_context *bld,
*/
const double lp_build_log2_polynomial[] = {
#if LOG_POLY_DEGREE == 6
3.11578814719469302614, -3.32419399085241980044, 2.59883907202499966007, -1.23152682416275988241, 0.318212422185251071475, -0.0344359067839062357313
3.11578814719469302614,
-3.32419399085241980044,
2.59883907202499966007,
-1.23152682416275988241,
0.318212422185251071475,
-0.0344359067839062357313
#elif LOG_POLY_DEGREE == 5
2.8882704548164776201, -2.52074962577807006663, 1.48116647521213171641, -0.465725644288844778798, 0.0596515482674574969533
2.8882704548164776201,
-2.52074962577807006663,
1.48116647521213171641,
-0.465725644288844778798,
0.0596515482674574969533
#elif LOG_POLY_DEGREE == 4
2.61761038894603480148, -1.75647175389045657003, 0.688243882994381274313, -0.107254423828329604454
2.61761038894603480148,
-1.75647175389045657003,
0.688243882994381274313,
-0.107254423828329604454
#elif LOG_POLY_DEGREE == 3
2.28330284476918490682, -1.04913055217340124191, 0.204446009836232697516
2.28330284476918490682,
-1.04913055217340124191,
0.204446009836232697516
#else
#error
#endif