16 Mar
2019
16 Mar
'19
11:45 p.m.
On Wed, 13 Mar 2019 00:09:17 +0100 (CET)
karl(a)aspodata.se wrote:
Will Godfrey:
Thanks, that seems to hold true for a mixture of AMD and Intel machines.
--
It wasn't me! (Well actually, it probably was)
... the hard part is not dodging what life throws at you,
but trying to catch the good bits.
Does anyone know if GCC will replace power of 2
multiplications/divisions of
unsigned integers with bit shifts?
Test on your system:
$ cat a.c
#include <stdint.h>
int main(int argc, char *argv[]) {
uint16_t b = argc * 2;
return b;
}
$ gcc -S a.c
$ cat a.s
...
main:
.LFB0:
.cfi_startproc
pushq %rbp
.cfi_def_cfa_offset 16
.cfi_offset 6, -16
movq %rsp, %rbp
.cfi_def_cfa_register 6
movl %edi, -20(%rbp)
movq %rsi, -32(%rbp)
movl -20(%rbp), %eax
addl %eax, %eax
movw %ax, -2(%rbp)
movzwl -2(%rbp), %eax
popq %rbp
.cfi_def_cfa 7, 8
ret
.cfi_endproc
...
$
It seems it just adds the value with itself here.
Regards,
/Karl Hammar