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Date: Tue, 19 Feb 2008 18:47:00 -0000
From: David Daney <ddaney@avtrex.com>
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To: Dave Korn <dave.korn@artimi.com>
Cc: gdb@sourceware.org
Subject: Re: (len % 1) != 0
References: <5800c1cc0802162157g3ac31acas4ae95585b9b2e263@mail.gmail.com><E1JQkG0-0005DD-0k@fencepost.gnu.org><5800c1cc0802170641g68ab2e5fte724cd076412333@mail.gmail.com><20080217152625.GA4810@caradoc.them.org><47BB03ED.5060708@baymicrosystems.com><007f01c87324$00f45a90$2e08a8c0@CAM.ARTIMI.COM> <18363.7810.91075.314867@gargle.gargle.HOWL> <008001c87325$6db805e0$2e08a8c0@CAM.ARTIMI.COM>
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Dave Korn wrote:
> On 19 February 2008 18:23, Paul Koning wrote:
> 
>>>>>>> "Dave" == Dave Korn <dave.korn@artimi.com> writes:
>>  Dave> On 19 February 2008 16:30, Sheng-Liang Song wrote:
>>  >> or
>>  >>
>>  >> (len & 1) != 0 <=> (len % 2) != 0
>>  >>
>>
>>  Dave> That would have the advantage of not requiring a divide
>>  Dave> operation :)
>>
>> It shouldn't matter -- the optimizer will do the right thing, as I
>> recall.
> 
>   NB len == signed int.
> 
>   Yes, it can simplify it to a bunch of shifts and sign extends and masks
> without using an explicit divide, but it's not as good as a simple AND
> operation.  (Maybe VRP in 4.x could handle that by knowing that the result of
> strlen has to be >= 0, but 3.x series won't do it).
> 

??  Not to be pedantic, but on 3.4.3 for mipsel-linux I get:

$ cat j.c
int f1 (int a)
{
     return (a % 2) != 0;
}
$ mipsel-linux-gcc -c -O3 j.c
$ mipsel-linux-objdump -d j.o

j.o:     file format elf32-tradlittlemips

Disassembly of section .text:

00000000 <f1>:
    0:   03e00008        jr      ra
    4:   30820001        andi    v0,a0,0x1