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Subject: Re: bug in roundup(3) from <sys/param.h>
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To: Wilco Dijkstra <Wilco.Dijkstra@arm.com>,
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Cc: 'GNU C Library' <libc-alpha@sourceware.org>
References: <PAWPR08MB898295545D7DDC1F4051E95F83C69@PAWPR08MB8982.eurprd08.prod.outlook.com>
From: Paul Eggert <eggert@cs.ucla.edu>
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On 1/17/23 11:16, Wilco Dijkstra via Libc-alpha wrote:
> So it seems best to state it only works on unsigned values (with y > 0 since division
> by zero is undefined behaviour of course) and it's implementation defined whether
> overflow wraps or saturates.

roundup works just fine on signed integers. Although x should be 
nonnegative and y should be positive, there's no requirement that either 
x or y must be unsigned.

This sort of thing matters in the C style I prefer nowadays, which is to 
use types like ptrdiff_t and idx_t instead of size_t, so that I can 
optionally enable runtime overflow checking that works.