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2043b3b47b
The old way of implementing it, float32(float64(x)), involves 2 roundings which can cause accuracy errors in some strange cases. Implement a runtime version of [u]int64tofloat32 which only does one rounding. Fixes #48807 Change-Id: Ie580be480bee4f3a479e58ef8dce23032f231704 Reviewed-on: https://go-review.googlesource.com/c/go/+/354429 Trust: Keith Randall <khr@golang.org> Run-TryBot: Keith Randall <khr@golang.org> TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: David Chase <drchase@google.com>
26 lines
699 B
Go
26 lines
699 B
Go
// Copyright 2021 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package runtime_test
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import (
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"testing"
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)
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func TestIssue48807(t *testing.T) {
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for _, i := range []uint64{
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0x8234508000000001, // from issue48807
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1<<56 + 1<<32 + 1,
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} {
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got := float32(i)
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dontwant := float32(float64(i))
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if got == dontwant {
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// The test cases above should be uint64s such that
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// this equality doesn't hold. These examples trigger
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// the case where using an intermediate float64 doesn't work.
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t.Errorf("direct float32 conversion doesn't work: arg=%x got=%x dontwant=%x", i, got, dontwant)
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}
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}
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}
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