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gallivm: Use nextafterf(0.5, 0.0) as rounding constant

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The common truncf(x + 0.5) fails for the floating-point value just less
than 0.5 (nextafterf(0.5, 0.0)). nextafterf(0.5, 0.0) + 0.5, after
rounding is 1.0, thus truncf does not produce the desired value.

The solution is to add nextafterf(0.5, 0.0) instead of 0.5 before
truncating. This works for all values.

Reviewed-by: Roland Scheidegger <sroland@vmware.com>
This commit is contained in:
Matt Turner
2018-11-21 12:13:19 -08:00
parent e2ad94d928
commit 2d48d5116b
1 changed files with 1 additions and 1 deletions
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src/gallium/auxiliary/gallivm/lp_bld_arit.c
+1 -1
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@@ -2477,7 +2477,7 @@ lp_build_iround(struct lp_build_context *bld,
else {
LLVMValueRef half;
half = lp_build_const_vec(bld->gallivm, type, 0.5);
half = lp_build_const_vec(bld->gallivm, type, nextafterf(0.5, 0.0));
if (type.sign) {
LLVMTypeRef vec_type = bld->vec_type;