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Fix random bugs #6

Merged
merged 4 commits into from
Dec 1, 2018
Merged

Fix random bugs #6

merged 4 commits into from
Dec 1, 2018

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robyoder
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Fixes #5

  1. Don't generate 8 random bytes when we only need 4.
  2. Fix performance and non-uniform bug in int31n.

Thanks, @Sc00bz!

@Sc00bz
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Sc00bz commented Nov 30, 2018

It should probably still panic if n is zero since "[0,n)" is not a valid range. Also "Based on Int32n from the math/rand package.." there is no Int32n it's Int31n.

@robyoder
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@Sc00bz it's not a valid range, but I don't think the panic is useful.

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Sc00bz commented Nov 30, 2018

Well setting n to zero is equivalent to a divide by zero which is a panic. Is there an equivalent in Go to C/C++'s assert() that are removed when not debugging? This way if there is weird behavior you can get this error when debugging.

jpgoldberg
jpgoldberg approved these changes Dec 1, 2018
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Thanks. The two fixes and the name cleanup are good things.

I do want consider what the proper behavior should be on a division by zero, but let's make that a separate issue.

util.go
b := make([]byte, 8)
// randomUint32 creates a random 32 bit unsigned integer
func randomUint32() uint32 {
b := make([]byte, 4)
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Thanks. I'm not sure why I originally had 8 in there. Probably because I can't do arithmetic.

util.go
// Based on Int31n from the math/rand package..
func randomUint32n(n uint32) uint32 {
if n <= 1 {
return 0
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I agree that we need to figure out more carefully what we want to happen in this case. This choice is fine for now, but we should create a separate issue for this.

@jpgoldberg jpgoldberg merged commit 3e0f92b into master Dec 1, 2018
@jpgoldberg jpgoldberg deleted the ry/random-bugs branch December 1, 2018 16:30
@jpgoldberg jpgoldberg mentioned this pull request Dec 1, 2018
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@robyoder @Sc00bz @jpgoldberg