gallivm: Refactor the Newton-Rapshon steps, and disable once again.
It causes a very ugly corruption on the Earth's halo on Google Earth.
This commit is contained in:
José Fonseca
parent
3c9b00e6e8
commit
eacb624a4a
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@ -1,6 +1,6 @@
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/**************************************************************************
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*
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* Copyright 2009 VMware, Inc.
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* Copyright 2009-2010 VMware, Inc.
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* All Rights Reserved.
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*
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* Permission is hereby granted, free of charge, to any person obtaining a
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@ -59,6 +59,19 @@
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#include "lp_bld_arit.h"
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/*
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* XXX: Increasing eliminates some artifacts, but adds others, most
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* noticeably corruption in the Earth halo in Google Earth.
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*/
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#define RCP_NEWTON_STEPS 0
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#define RSQRT_NEWTON_STEPS 0
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#define EXP_POLY_DEGREE 3
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#define LOG_POLY_DEGREE 5
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/**
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* Generate min(a, b)
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* No checks for special case values of a or b = 1 or 0 are done.
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@ -1248,6 +1261,31 @@ lp_build_sqrt(struct lp_build_context *bld,
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}
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/**
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* Do one Newton-Raphson step to improve reciprocate precision:
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*
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* x_{i+1} = x_i * (2 - a * x_i)
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*
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* See also:
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* - http://en.wikipedia.org/wiki/Division_(digital)#Newton.E2.80.93Raphson_division
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* - http://softwarecommunity.intel.com/articles/eng/1818.htm
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*/
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static INLINE LLVMValueRef
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lp_build_rcp_refine(struct lp_build_context *bld,
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LLVMValueRef a,
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LLVMValueRef rcp_a)
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{
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LLVMValueRef two = lp_build_const_vec(bld->type, 2.0);
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LLVMValueRef res;
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res = LLVMBuildFMul(bld->builder, a, rcp_a, "");
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res = LLVMBuildFSub(bld->builder, two, res, "");
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res = LLVMBuildFMul(bld->builder, rcp_a, res, "");
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return res;
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}
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LLVMValueRef
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lp_build_rcp(struct lp_build_context *bld,
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LLVMValueRef a)
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@ -1269,38 +1307,49 @@ lp_build_rcp(struct lp_build_context *bld,
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return LLVMConstFDiv(bld->one, a);
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if(util_cpu_caps.has_sse && type.width == 32 && type.length == 4) {
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/*
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* XXX: Added precision is not always necessary, so only enable this
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* when we have a better system in place to track minimum precision.
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*/
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#if 1
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/*
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* Do one Newton-Raphson step to improve precision:
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*
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* x1 = (2 - a * rcp(a)) * rcp(a)
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*/
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LLVMValueRef two = lp_build_const_vec(bld->type, 2.0);
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LLVMValueRef rcp_a;
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LLVMValueRef res;
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unsigned i;
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rcp_a = lp_build_intrinsic_unary(bld->builder, "llvm.x86.sse.rcp.ps", lp_build_vec_type(type), a);
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res = lp_build_intrinsic_unary(bld->builder, "llvm.x86.sse.rcp.ps", bld->vec_type, a);
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res = LLVMBuildFMul(bld->builder, a, rcp_a, "");
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res = LLVMBuildFSub(bld->builder, two, res, "");
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res = LLVMBuildFMul(bld->builder, res, rcp_a, "");
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for (i = 0; i < RCP_NEWTON_STEPS; ++i) {
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res = lp_build_rcp_refine(bld, a, res);
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}
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return res;
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#else
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return lp_build_intrinsic_unary(bld->builder, "llvm.x86.sse.rcp.ps", lp_build_vec_type(type), a);
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#endif
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}
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return LLVMBuildFDiv(bld->builder, bld->one, a, "");
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}
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/**
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* Do one Newton-Raphson step to improve rsqrt precision:
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*
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* x_{i+1} = 0.5 * x_i * (3.0 - a * x_i * x_i)
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*
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* See also:
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* - http://softwarecommunity.intel.com/articles/eng/1818.htm
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*/
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static INLINE LLVMValueRef
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lp_build_rsqrt_refine(struct lp_build_context *bld,
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LLVMValueRef a,
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LLVMValueRef rsqrt_a)
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{
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LLVMValueRef half = lp_build_const_vec(bld->type, 0.5);
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LLVMValueRef three = lp_build_const_vec(bld->type, 3.0);
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LLVMValueRef res;
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res = LLVMBuildFMul(bld->builder, rsqrt_a, rsqrt_a, "");
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res = LLVMBuildFMul(bld->builder, a, res, "");
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res = LLVMBuildFSub(bld->builder, three, res, "");
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res = LLVMBuildFMul(bld->builder, rsqrt_a, res, "");
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res = LLVMBuildFMul(bld->builder, half, res, "");
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return res;
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}
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/**
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* Generate 1/sqrt(a)
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*/
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@ -1314,8 +1363,18 @@ lp_build_rsqrt(struct lp_build_context *bld,
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assert(type.floating);
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if(util_cpu_caps.has_sse && type.width == 32 && type.length == 4)
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return lp_build_intrinsic_unary(bld->builder, "llvm.x86.sse.rsqrt.ps", lp_build_vec_type(type), a);
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if(util_cpu_caps.has_sse && type.width == 32 && type.length == 4) {
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LLVMValueRef res;
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unsigned i;
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res = lp_build_intrinsic_unary(bld->builder, "llvm.x86.sse.rsqrt.ps", bld->vec_type, a);
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for (i = 0; i < RSQRT_NEWTON_STEPS; ++i) {
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res = lp_build_rsqrt_refine(bld, a, res);
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}
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return res;
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}
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return lp_build_rcp(bld, lp_build_sqrt(bld, a));
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}
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@ -1821,10 +1880,6 @@ lp_build_log(struct lp_build_context *bld,
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}
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#define EXP_POLY_DEGREE 3
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#define LOG_POLY_DEGREE 5
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/**
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* Generate polynomial.
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* Ex: coeffs[0] + x * coeffs[1] + x^2 * coeffs[2].
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