From: Bruno Haible <bruno@clisp.org>
To: bug-gnulib@gnu.org
Cc: "Tim Rühsen" <tim.ruehsen@gmx.de>
Subject: Re: clang-10 warning in hash.c
Date: Mon, 27 Jan 2020 14:09:50 +0100 [thread overview]
Message-ID: <3695940.OeVvW2AmiG@omega> (raw)
In-Reply-To: <ac0b82a1-816f-2fef-7009-2d4475531296@gmx.de>
Hi Tim,
> Not sure if the compiler is correct here, but maybe worth a look:
>
> hash.c:549:11: error: implicit conversion from 'unsigned long' to
> 'float' changes value from 18446744073709551615 to 18446744073709551616
> [-Werror,-Wimplicit-int-float-conversion]
> if (SIZE_MAX <= new_candidate)
> ^~~~~~~~ ~~
> /usr/include/stdint.h:227:22: note: expanded from macro 'SIZE_MAX'
> # define SIZE_MAX (18446744073709551615UL)
> ^~~~~~~~~~~~~~~~~~~~~~
This warning is pointless, because
- Since the next float below 18446744073709551616 = 0x10000000000000000
would be 18446742974197923840 = 0xFFFFFF0000000000
the comparison result is the same for the two values ...615 and ...616.
- The compiler inserts the implicit conversion only because of the '<='
operator.
IMO you should file a ticket with the clang people.
Inserting a cast to 'double'
if ((double) SIZE_MAX <= (double) new_candidate)
would not help, because
the next double-float below 18446744073709551616 = 0x10000000000000000
would be 18446744073709549568 = 0xFFFFFFFFFFFFF800
Bruno
next prev parent reply other threads:[~2020-01-27 13:10 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-27 10:58 clang-10 warning in hash.c Tim Rühsen
2020-01-27 13:09 ` Bruno Haible [this message]
2020-01-27 20:16 ` Paul Eggert
2020-01-27 21:03 ` Bruno Haible
2020-01-28 2:08 ` Bruno Haible
2020-01-30 15:35 ` Tim Rühsen
2020-01-30 17:50 ` bugs.llvm.org Bruno Haible
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