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gallicm: Newton-Raphson step to improve precision.

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Disabled as it doesn't make VS/PSPrecision DCT happy, and it would
unnecessarily slow some cases where it is not needed.
This commit is contained in:
José Fonseca
2010-05-03 17:06:57 +01:00
parent 9b02f41cac
commit a9d1a85f81
1 changed files with 27 additions and 2 deletions
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src/gallium/auxiliary/gallivm/lp_bld_arit.c
+27 -2
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@@ -1177,9 +1177,34 @@ lp_build_rcp(struct lp_build_context *bld,
if(LLVMIsConstant(a))
return LLVMConstFDiv(bld->one, a);
if(util_cpu_caps.has_sse && type.width == 32 && type.length == 4)
/* FIXME: improve precision */
if(util_cpu_caps.has_sse && type.width == 32 && type.length == 4) {
/*
* XXX: Added precision is not always necessary, so only enable this
* when we have a better system in place to track minimum precision.
*/
#if 0
/*
* Do one Newton-Raphson step to improve precision:
*
* x1 = (2 - a * rcp(a)) * rcp(a)
*/
LLVMValueRef two = lp_build_const_vec(bld->type, 2.0);
LLVMValueRef rcp_a;
LLVMValueRef res;
rcp_a = lp_build_intrinsic_unary(bld->builder, "llvm.x86.sse.rcp.ps", lp_build_vec_type(type), a);
res = LLVMBuildMul(bld->builder, a, rcp_a, "");
res = LLVMBuildSub(bld->builder, two, res, "");
res = LLVMBuildMul(bld->builder, res, rcp_a, "");
return rcp_a;
#else
return lp_build_intrinsic_unary(bld->builder, "llvm.x86.sse.rcp.ps", lp_build_vec_type(type), a);
#endif
}
return LLVMBuildFDiv(bld->builder, bld->one, a, "");
}