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nir: use Horner's method for atan

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Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/30934>
This commit is contained in:
Alyssa Rosenzweig
2024-08-29 18:57:18 -04:00
committed by Marge Bot
parent 0c81a29db6
commit 4fc3e34f2f
1 changed files with 14 additions and 31 deletions
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45
src/compiler/nir/nir_builtin_builder.c
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@@ -25,6 +25,7 @@
#include <math.h>
#include "nir.h"
#include "nir_builder.h"
#include "nir_builtin_builder.h"
nir_def *
@@ -158,20 +159,6 @@ nir_upsample(nir_builder *b, nir_def *hi, nir_def *lo)
return nir_vec(b, res, lo->num_components);
}
/**
* Compute xs[0] + xs[1] + xs[2] + ... using fadd.
*/
static nir_def *
build_fsum(nir_builder *b, nir_def **xs, int terms)
{
nir_def *accum = xs[0];
for (int i = 1; i < terms; i++)
accum = nir_fadd(b, accum, xs[i]);
return accum;
}
nir_def *
nir_atan(nir_builder *b, nir_def *y_over_x)
{
@@ -191,30 +178,26 @@ nir_atan(nir_builder *b, nir_def *y_over_x)
nir_fmax(b, abs_y_over_x, one));
/*
* approximate atan by evaluating polynomial:
* approximate atan by evaluating polynomial using Horner's method:
*
* x * 0.9999793128310355 - x^3 * 0.3326756418091246 +
* x^5 * 0.1938924977115610 - x^7 * 0.1173503194786851 +
* x^9 * 0.0536813784310406 - x^11 * 0.0121323213173444
*/
nir_def *x_2 = nir_fmul(b, x, x);
nir_def *x_3 = nir_fmul(b, x_2, x);
nir_def *x_5 = nir_fmul(b, x_3, x_2);
nir_def *x_7 = nir_fmul(b, x_5, x_2);
nir_def *x_9 = nir_fmul(b, x_7, x_2);
nir_def *x_11 = nir_fmul(b, x_9, x_2);
nir_def *polynomial_terms[] = {
nir_fmul_imm(b, x, 0.9999793128310355f),
nir_fmul_imm(b, x_3, -0.3326756418091246f),
nir_fmul_imm(b, x_5, 0.1938924977115610f),
nir_fmul_imm(b, x_7, -0.1173503194786851f),
nir_fmul_imm(b, x_9, 0.0536813784310406f),
nir_fmul_imm(b, x_11, -0.0121323213173444f),
float coeffs[] = {
-0.0121323213173444f, 0.0536813784310406f,
-0.1173503194786851f, 0.1938924977115610f,
-0.3326756418091246f, 0.9999793128310355f
};
nir_def *tmp =
build_fsum(b, polynomial_terms, ARRAY_SIZE(polynomial_terms));
nir_def *x_2 = nir_fmul(b, x, x);
nir_def *res = nir_imm_floatN_t(b, coeffs[0], bit_size);
for (unsigned i = 1; i < ARRAY_SIZE(coeffs); ++i) {
res = nir_ffma_imm2(b, res, x_2, coeffs[i]);
}
nir_def *tmp = nir_fmul(b, x, res);
/* range-reduction fixup */
tmp = nir_ffma(b,