* [9fans] c99 div and mod round toward zero
@ 2006-04-16 1:53 erik quanstrom
2006-04-16 3:15 ` Russ Cox
2006-04-16 3:56 ` geoff
0 siblings, 2 replies; 5+ messages in thread
From: erik quanstrom @ 2006-04-16 1:53 UTC (permalink / raw)
To: 9fans
according to /sys/src/cmd/cc/c99:
Not done (yet?):
[...]
25. Division and mod truncate toward zero.
on 8c this works as expected. i.e.
; cat mod.c
#include <u.h>
#include <libc.h>
void
main(void)
{
fprint(2, "-22/7 = %d\n", -22/7);
fprint(2, "-22%%7 = %d\n", -22%7);
}
; 8c mod.c && 8l mod.8 && 8.out
-22 7 = -3
-22 % 7 = -1
is this fixed, or an archiitechture-dependent thing? i don't
have a way of checking anything else.
- erik
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [9fans] c99 div and mod round toward zero
2006-04-16 1:53 [9fans] c99 div and mod round toward zero erik quanstrom
@ 2006-04-16 3:15 ` Russ Cox
2006-04-16 3:56 ` geoff
1 sibling, 0 replies; 5+ messages in thread
From: Russ Cox @ 2006-04-16 3:15 UTC (permalink / raw)
To: 9fans
> is this fixed, or an archiitechture-dependent thing? i don't
> have a way of checking anything else.
traditionally it is architecture+compiler dependent.
off the top of my head i don't know what the other
compilers do.
russ
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [9fans] c99 div and mod round toward zero
2006-04-16 1:53 [9fans] c99 div and mod round toward zero erik quanstrom
2006-04-16 3:15 ` Russ Cox
@ 2006-04-16 3:56 ` geoff
2006-04-16 5:33 ` Russ Cox
1 sibling, 1 reply; 5+ messages in thread
From: geoff @ 2006-04-16 3:56 UTC (permalink / raw)
To: 9fans
I took Erik's question to be whether 8c rounded to zero because the
x86 (or 8c) does it that way or because the common C compiler code had
been changed to force C99 behaviour.
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [9fans] c99 div and mod round toward zero
2006-04-16 3:56 ` geoff
@ 2006-04-16 5:33 ` Russ Cox
0 siblings, 0 replies; 5+ messages in thread
From: Russ Cox @ 2006-04-16 5:33 UTC (permalink / raw)
To: 9fans
> I took Erik's question to be whether 8c rounded to zero because the
> x86 (or 8c) does it that way or because the common C compiler code had
> been changed to force C99 behaviour.
the former.
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [9fans] c99 div and mod round toward zero
@ 2006-04-16 3:48 dmr
0 siblings, 0 replies; 5+ messages in thread
From: dmr @ 2006-04-16 3:48 UTC (permalink / raw)
To: 9fans
> is this [rounding to 0] fixed, or an archiitechture-dependent thing? i don't
> have a way of checking anything else.
In C89 it was allowed to vary by architecture (subject to obvious consistency
constraints). In C99 the result is well-determined, and does round to 0.
This is consistent with the usual math convention, but
in fact not necessarily best (e.g. for graphics, as Rob has pointed out).
Dennis
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2006-04-16 5:33 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
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2006-04-16 1:53 [9fans] c99 div and mod round toward zero erik quanstrom
2006-04-16 3:15 ` Russ Cox
2006-04-16 3:56 ` geoff
2006-04-16 5:33 ` Russ Cox
2006-04-16 3:48 dmr
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