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math/big: ProbablyPrime accepts nonpositive integers as rounds count #9509

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ALTree opened this issue Jan 5, 2015 · 4 comments
Closed

math/big: ProbablyPrime accepts nonpositive integers as rounds count #9509

ALTree opened this issue Jan 5, 2015 · 4 comments
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Documentation FrozenDueToAge
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Go1.5

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@ALTree
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ALTree commented Jan 5, 2015

Even though only positive integers make sense, ProbablyPrime accepts null and negative integers for the "number of Miller-Rabin rounds" parameter, and happily output true (i.e prime) when given n < 1.

package main

import "math/big"

func main() {
    n := new(big.Int)
    n.SetString("5041", 10) // 71 * 71
    println(n.ProbablyPrime(0)) // true
}

http://play.golang.org/p/vLwhlt3xsC
@griesemer griesemer added this to the Go1.5 milestone Jan 5, 2015
@griesemer griesemer self-assigned this Jan 5, 2015
@griesemer
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Easy to add an extra test if that's desired and documentation is not good enough.

@ALTree
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ALTree commented Jan 5, 2015

Easy to patch but I'm not sure whether

  • Leave the code, change documentation ("no Miller-Rabin test is done when n < 1")
  • Panic on n < 1
  • Ignore the given n and set a custom nice value (i.e. 25) on n < 1

@griesemer griesemer reopened this Jan 5, 2015
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I'd document that n must be > 0 and panic with an appropriate message if it's not. That makes it clear and prevents surprises.

@minux
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minux commented Jan 5, 2015

Sent https://golang.org/cl/2313

@minux minux closed this as completed in 4317869 Jan 5, 2015
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