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math: exp sometimes returns wrong values on overflow on amd64 #18912

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ALTree opened this issue Feb 3, 2017 · 1 comment
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math: exp sometimes returns wrong values on overflow on amd64 #18912

ALTree opened this issue Feb 3, 2017 · 1 comment
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FrozenDueToAge NeedsFix The path to resolution is known, but the work has not been done.
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Go1.9

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@ALTree
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ALTree commented Feb 3, 2017

go version devel +12c58bbf81 Fri Feb 3 06:52:46 2017 +0000 linux/amd64

Documentation says:

Very large values overflow to 0 or +Inf

But that's not always true (at least not when using the assembly implementation on amd64). Example:

package main

import (
	"fmt"
	"math"
)

func main() {
	fmt.Println(math.Exp(1.48852223e+09))
	fmt.Println(math.Exp(1.4885222e+09))
	fmt.Println(math.Exp(1.48852e+09))
}

Gives

0.0027127673070219977
2.5385055740655363e-16
+Inf
@ALTree ALTree added the NeedsFix The path to resolution is known, but the work has not been done. label Feb 3, 2017
@ALTree ALTree added this to the Go1.9 milestone Feb 3, 2017
@ALTree ALTree mentioned this issue Feb 3, 2017
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CL https://golang.org/cl/36271 mentions this issue.

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