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llvmpipe: Efficient implementations of pow/exp/log/exp2/log2

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This commit is contained in:
José Fonseca
2009-08-12 10:35:50 +01:00
parent 90e9a4d4f9
commit 844f802a70
1 changed files with 99 additions and 38 deletions
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src/gallium/drivers/llvmpipe/lp_bld_arit.c
+99 -38
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@@ -45,6 +45,7 @@
*/
#include "util/u_memory.h"
#include "util/u_debug.h"
#include "util/u_string.h"
@@ -651,37 +652,36 @@ lp_build_sin(struct lp_build_context *bld,
LLVMValueRef
lp_build_pow(struct lp_build_context *bld,
LLVMValueRef a,
LLVMValueRef b)
LLVMValueRef x,
LLVMValueRef y)
{
const union lp_type type = bld->type;
LLVMTypeRef vec_type = lp_build_vec_type(type);
char intrinsic[32];
/* TODO: optimize the constant case */
if(LLVMIsConstant(x) && LLVMIsConstant(y))
debug_printf("%s: inefficient/imprecise constant arithmetic\n");
assert(type.floating);
util_snprintf(intrinsic, sizeof intrinsic, "llvm.pow.v%uf%u", type.length, type.width);
return lp_build_intrinsic_binary(bld->builder, intrinsic, vec_type, a, b);
return lp_build_exp2(bld, lp_build_mul(bld, lp_build_log2(bld, x), y));
}
LLVMValueRef
lp_build_exp(struct lp_build_context *bld,
LLVMValueRef a)
LLVMValueRef x)
{
/* FIXME: optimize */
return lp_build_pow(bld, lp_build_const_uni(bld->type, 2.7182818284590452354), a);
/* log2(e) = 1/log(2) */
LLVMValueRef log2e = lp_build_const_uni(bld->type, 1.4426950408889634);
return lp_build_mul(bld, log2e, lp_build_exp2(bld, x));
}
LLVMValueRef
lp_build_log(struct lp_build_context *bld,
LLVMValueRef a)
LLVMValueRef x)
{
/* FIXME: implement */
return bld->undef;
/* log(2) */
LLVMValueRef log2 = lp_build_const_uni(bld->type, 1.4426950408889634);
return lp_build_mul(bld, log2, lp_build_exp2(bld, x));
}
@@ -699,6 +699,10 @@ lp_build_polynomial(struct lp_build_context *bld,
LLVMValueRef res = NULL;
unsigned i;
/* TODO: optimize the constant case */
if(LLVMIsConstant(x))
debug_printf("%s: inefficient/imprecise constant arithmetic\n");
for (i = num_coeffs; i--; ) {
LLVMValueRef coeff = lp_build_const_uni(type, coeffs[i]);
if(res)
@@ -714,15 +718,83 @@ lp_build_polynomial(struct lp_build_context *bld,
}
/**
* Minimax polynomial fit of 2**x, in range [-0.5, 0.5[
*/
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
#elif EXP_POLY_DEGREE == 4
1.0000026, 6.9300383e-1, 2.4144275e-1, 5.2011464e-2, 1.3534167e-2
#elif EXP_POLY_DEGREE == 3
9.9992520e-1, 6.9583356e-1, 2.2606716e-1, 7.8024521e-2
#elif EXP_POLY_DEGREE == 2
1.0017247, 6.5763628e-1, 3.3718944e-1
#else
#error
#endif
};
LLVMValueRef
lp_build_exp2(struct lp_build_context *bld,
LLVMValueRef a)
LLVMValueRef x)
{
/* FIXME: optimize */
return lp_build_pow(bld, lp_build_const_uni(bld->type, 2.0), a);
const union lp_type type = bld->type;
LLVMTypeRef vec_type = lp_build_vec_type(type);
LLVMTypeRef int_vec_type = lp_build_int_vec_type(type);
LLVMValueRef ipart;
LLVMValueRef fpart, expipart, expfpart;
/* TODO: optimize the constant case */
if(LLVMIsConstant(x))
debug_printf("%s: inefficient/imprecise constant arithmetic\n");
assert(type.floating && type.width == 32);
x = lp_build_min(bld, x, lp_build_const_uni(type, 129.0));
x = lp_build_max(bld, x, lp_build_const_uni(type, -126.99999));
/* ipart = int(x - 0.5) */
ipart = LLVMBuildSub(bld->builder, x, lp_build_const_uni(type, 0.5f), "");
ipart = LLVMBuildFPToSI(bld->builder, ipart, int_vec_type, "");
/* fpart = x - ipart */
fpart = LLVMBuildSIToFP(bld->builder, ipart, vec_type, "");
fpart = LLVMBuildSub(bld->builder, x, fpart, "");
/* expipart = (float) (1 << ipart) */
expipart = LLVMBuildAdd(bld->builder, ipart, lp_build_int_const_uni(type, 127), "");
expipart = LLVMBuildShl(bld->builder, expipart, lp_build_int_const_uni(type, 23), "");
expipart = LLVMBuildBitCast(bld->builder, expipart, vec_type, "");
expfpart = lp_build_polynomial(bld, fpart, lp_build_exp2_polynomial,
Elements(lp_build_exp2_polynomial));
return LLVMBuildMul(bld->builder, expipart, expfpart, "");
}
/**
* Minimax polynomial fit of log2(x)/(x - 1), for x in range [1, 2[
* These coefficients can be generate with
* http://www.boost.org/doc/libs/1_36_0/libs/math/doc/sf_and_dist/html/math_toolkit/toolkit/internals2/minimax.html
*/
const double lp_build_log2_polynomial[] = {
#if LOG_POLY_DEGREE == 6
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
#elif LOG_POLY_DEGREE == 4
2.61761038894603480148, -1.75647175389045657003, 0.688243882994381274313, -0.107254423828329604454
#elif LOG_POLY_DEGREE == 3
2.28330284476918490682, -1.04913055217340124191, 0.204446009836232697516
#else
#error
#endif
};
/**
* See http://www.devmaster.net/forums/showthread.php?p=43580
*/
@@ -744,6 +816,12 @@ lp_build_log2(struct lp_build_context *bld,
LLVMValueRef mant;
LLVMValueRef logmant;
/* TODO: optimize the constant case */
if(LLVMIsConstant(x))
debug_printf("%s: inefficient/imprecise constant arithmetic\n");
assert(type.floating && type.width == 32);
/* exp = (float) exponent(x) */
exp = LLVMBuildAnd(bld->builder, i, expmask, "");
exp = LLVMBuildLShr(bld->builder, exp, lp_build_int_const_uni(type, 23), "");
@@ -755,25 +833,8 @@ lp_build_log2(struct lp_build_context *bld,
mant = LLVMBuildOr(bld->builder, mant, one, "");
mant = LLVMBuildSIToFP(bld->builder, mant, vec_type, "");
/* Minimax polynomial fit of log2(x)/(x - 1), for x in range [1, 2[
* These coefficients can be generate with
* http://www.boost.org/doc/libs/1_36_0/libs/math/doc/sf_and_dist/html/math_toolkit/toolkit/internals2/minimax.html
*/
const double polynomial[] = {
#if LOG_POLY_DEGREE == 6
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
#elif LOG_POLY_DEGREE == 4
2.61761038894603480148, -1.75647175389045657003, 0.688243882994381274313, -0.107254423828329604454
#elif LOG_POLY_DEGREE == 3
2.28330284476918490682, -1.04913055217340124191, 0.204446009836232697516
#else
#error
#endif
};
logmant = lp_build_polynomial(bld, mant, polynomial, sizeof(polynomial)/sizeof(polynomial[0]));
logmant = lp_build_polynomial(bld, mant, lp_build_log2_polynomial,
Elements(lp_build_log2_polynomial));
/* This effectively increases the polynomial degree by one, but ensures that log2(1) == 0*/
logmant = LLVMBuildMul(bld->builder, logmant, LLVMBuildMul(bld->builder, mant, bld->one, ""), "");