If we really want to squeek out optimizations, judicious use
of 'register' might help even...
But after awhile things start getting silly :)
> On Nov 24, 2015, at 1:04 PM, Yann Ylavic <ylavic....@gmail.com> wrote:
>
> I did some testing with different implémentations and my results show
> that fastest one is:
>
> int ap_casecmpstr_2(const char *s1, const char *s2)
> {
> size_t i;
> const unsigned char *ps1 = (const unsigned char *) s1;
> const unsigned char *ps2 = (const unsigned char *) s2;
>
> for (i = 0; ; ++i) {
> const int c1 = ps1[i];
> const int c2 = ps2[i];
>
> if (c1 != c2) {
> return c1 - c2;
> }
> if (!c1) {
> break;
> }
> }
> return (0);
> }
>
> int ap_casecmpstrn_2(const char *s1, const char *s2, size_t n)
> {
> size_t i;
> const unsigned char *ps1 = (const unsigned char *) s1;
> const unsigned char *ps2 = (const unsigned char *) s2;
>
> for (i = 0; i < n; ++i) {
> const int c1 = ps1[i];
> const int c2 = ps2[i];
>
> if (c1 != c2) {
> return c1 - c2;
> }
> if (!c1) {
> break;
> }
> }
> return (0);
> }
>
> Some samples (test program attached):
>
> $ gcc -Wall -O2 newtest.c -o newtest -lrt
> $ for i in `seq 0 2`; do
> ./newtest $i 150000000 \
> xcxcxcxcxcxcxcxcxcxcwwwwwwwwwwaaaaaaaaaa \
> xcxcxcxcxcxcxcxcxcxcwwwwwwwwwwaaaaaaaaaa \
> 0
> done
> - str[n]casecmp (nb=150000000, len=0)
> time = 8.444547186 : res = 0
> - ap_casecmpstr[n] (nb=150000000, len=0)
> time = 8.299781468 : res = 0
> - ap_casecmpstr[n] w/ index (nb=150000000, len=0)
> time = 6.148787259 : res = 0
>
> That's ~30% better.
>
> $ gcc -Wall -Os newtest.c -o newtest -lrt
> $ for i in `seq 0 2`; do
> ./newtest $i 150000000 \
> xcxcxcxcxcxcxcxcxcxcwwwwwwwwwwaaaaaaaaaa \
> xcxcxcxcxcxcxcxcxcxcwwwwwwwwwwaaaaaaaaaa \
> 0
> done
> - str[n]casecmp (nb=150000000, len=0)
> time = 8.528311136 : res = 0
> - ap_casecmpstr[n] (nb=150000000, len=0)
> time = 10.150553381 : res = 0
> - ap_casecmpstr[n] w/ index (nb=150000000, len=0)
> time = 9.758638566 : res = 0
>
> The string.h's str[n]casecmp beat us with -Os, still this new
> implementation is better than the current one.
>
> WDYT, should I commit these new versions?
> <newtest.c>
