From: Eric Dumazet <[EMAIL PROTECTED]> Date: Thu, 19 Apr 2007 16:14:23 +0200
> On Wed, 18 Apr 2007 13:04:22 -0700 (PDT) > David Miller <[EMAIL PROTECTED]> wrote: > > > > > Although I don't think gcc does anything fancy since we don't > > use memcmp(). It's a tradeoff, we'd like to use unsigned long > > comparisons when both objects are aligned correctly but we also > > don't want it to use any more than one potentially mispredicted > > branch. > > Again, memcmp() *cannot* be optimized, because its semantic is to compare > bytes. > > memcpy() can take into account alignement if known at compile time, not > memcmp() > > http://lists.openwall.net/netdev/2007/03/13/31 I was prehaps thinking about strlen() where I know several implementations work a word at a time even though it is a byte-based operation: -------------------- #define LO_MAGIC 0x01010101 #define HI_MAGIC 0x80808080 ... sethi %hi(HI_MAGIC), %o4 ... or %o4, %lo(HI_MAGIC), %o3 ... sethi %hi(LO_MAGIC), %o4 ... or %o4, %lo(LO_MAGIC), %o2 ... 8: ld [%o0], %o5 2: sub %o5, %o2, %o4 andcc %o4, %o3, %g0 be,pt %icc, 8b add %o0, 4, %o0 -------------------- I figured some similar trick could be done with strcmp() and memcmp(). - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
