Re: (len % 1) != 0

[David Daney <ddaney at avtrex dot com>]

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