Messages in this thread | | | Date | Thu, 17 Nov 2022 03:05:14 +0100 | From | "Jason A. Donenfeld" <> | Subject | Re: [PATCH v2 3/3] treewide: use get_random_u32_between() when possible |
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On Thu, Nov 17, 2022 at 12:55:47AM +0100, Jason A. Donenfeld wrote: > 1) How/whether to make f(0, UR2_MAX) safe, > - without additional 64-bit arithmetic, > - minimizing the number of branches. > I have a few ideas I'll code golf for a bit. > I think I can make progress with (1) alone by fiddling around with > godbolt enough, like usual.
The code gen is definitely worse.
Original half-open interval:
return floor + get_random_u32_below(ceil - floor);
Suggested fully closed interval:
ceil = ceil - floor + 1; return likely(ceil) ? floor + get_random_u32_below(ceil) : get_random_u32();
Is the worse code gen actually worth it? Options:
a) Decide worse codegen is worth it. b) Declare f(0, U32_MAX) undefined and just not handle it. c) Stick with original half-open interval that doesn't have this problem.
Jason
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