Mesa (master): gallivm: Improve lp_build_rcp_refine.
GitLab Mirror
gitlab-mirror at kemper.freedesktop.org
Fri Jun 28 10:48:19 UTC 2019
Module: Mesa
Branch: master
Commit: 35734129819ca7795adb9145123eb4eafea3a562
URL: http://cgit.freedesktop.org/mesa/mesa/commit/?id=35734129819ca7795adb9145123eb4eafea3a562
Author: Jose Fonseca <jfonseca at vmware.com>
Date: Fri May 31 17:10:40 2019 +0100
gallivm: Improve lp_build_rcp_refine.
Use the alternative more accurate expression from
https://en.wikipedia.org/wiki/Division_algorithm#Newton%E2%80%93Raphson_division
v2: Use lp_build_fmuladd as suggested by Roland
Tested by enabling this code path, and running lp_test_arit.
Reviewed-by: Roland Scheidegger <sroland at vmware.com>
---
src/gallium/auxiliary/gallivm/lp_bld_arit.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
diff --git a/src/gallium/auxiliary/gallivm/lp_bld_arit.c b/src/gallium/auxiliary/gallivm/lp_bld_arit.c
index 02fb81afe51..c4931c0b230 100644
--- a/src/gallium/auxiliary/gallivm/lp_bld_arit.c
+++ b/src/gallium/auxiliary/gallivm/lp_bld_arit.c
@@ -2707,11 +2707,11 @@ lp_build_sqrt(struct lp_build_context *bld,
/**
* Do one Newton-Raphson step to improve reciprocate precision:
*
- * x_{i+1} = x_i * (2 - a * x_i)
+ * x_{i+1} = x_i + x_i * (1 - a * x_i)
*
* XXX: Unfortunately this won't give IEEE-754 conformant results for 0 or
* +/-Inf, giving NaN instead. Certain applications rely on this behavior,
- * such as Google Earth, which does RCP(RSQRT(0.0) when drawing the Earth's
+ * such as Google Earth, which does RCP(RSQRT(0.0)) when drawing the Earth's
* halo. It would be necessary to clamp the argument to prevent this.
*
* See also:
@@ -2724,12 +2724,12 @@ lp_build_rcp_refine(struct lp_build_context *bld,
LLVMValueRef rcp_a)
{
LLVMBuilderRef builder = bld->gallivm->builder;
- LLVMValueRef two = lp_build_const_vec(bld->gallivm, bld->type, 2.0);
+ LLVMValueRef neg_a;
LLVMValueRef res;
- res = LLVMBuildFMul(builder, a, rcp_a, "");
- res = LLVMBuildFSub(builder, two, res, "");
- res = LLVMBuildFMul(builder, rcp_a, res, "");
+ neg_a = LLVMBuildFNeg(builder, a, "");
+ res = lp_build_fmuladd(builder, neg_a, rcp_a, bld->one);
+ res = lp_build_fmuladd(builder, res, rcp_a, rcp_a);
return res;
}
More information about the mesa-commit
mailing list