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Bug in overflow multiplication of uint type. #652

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dmitshur opened this issue Jun 24, 2017 · 0 comments
Open

Bug in overflow multiplication of uint type. #652

dmitshur opened this issue Jun 24, 2017 · 0 comments
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bug NeedsFix

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@dmitshur
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This might affect int type too, I haven't verified.

It does not affect uintptr, nor uint32.

package main

import (
	"fmt"
)

func main() {
	x := uint(4294967295)
	fmt.Println(x * x)
	// Output (gc):       1
	// Output (GopherJS): 0
}

https://play.golang.org/p/gY-qQ51AyZ
https://gopherjs.github.io/playground/#/gY-qQ51AyZ

/cc @neelance

I found this because math/big changed type of big.Word from uintptr in Go 1.8 to uint in Go 1.9, and it broke the majority of its tests.
dmitshur added a commit that referenced this issue Jun 24, 2017
@dmitshur
compiler/natives/src/math/big: Remove bitLen, override Word.
b508517 
math/big package no longer has a bitLen low-level function,
so it can be removed.

In Go 1.9, the type of big.Word has changed from uintptr
to uint. Due to issue #652 with uint multiplication with
overflows, we use a workaround of overriding type of Word
back to uintptr. This should be undone once #652 is fixed.

Fixes:

	$ gopherjs test --short math/big
	$GOROOT/src/math/big/big.go:39:9: undeclared name: bitLen_g
dmitshur added a commit that referenced this issue Aug 25, 2017
@dmitshur
compiler/natives/src/math/big: Remove bitLen, override Word.
c8a99bb 
math/big package no longer has a bitLen low-level function,
so it can be removed.

In Go 1.9, the type of big.Word has changed from uintptr
to uint. Due to issue #652 with uint multiplication with
overflows, we use a workaround of overriding type of Word
back to uintptr. This should be undone once #652 is fixed.

Fixes:

	$ gopherjs test --short math/big
	$GOROOT/src/math/big/big.go:39:9: undeclared name: bitLen_g
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@dmitshur