On Thu, 5 Sep 2002, Hirokazu Takahashi wrote:
> > And again, I think you'll find the rotate faster on at least some x86 cores.
>
> Yeah, I replaced "bswap %eax" with "roll $8,%eax" which would be more
> familier to us.
That's up to you. Since the bswap or roll are only in the conditional,
hopefully infrequently used paths of an odd buffer address, I don't
believe that selecting one or the other has any measurable impact.
> +25:
> + testl $1, %esi
> + jz 30f
> + # buf is odd
> + dec %ecx
> + jl 90f
> + roll $8, %eax
> + movzbl (%esi), %ebx
> + shll $8, %ebx
> + addl %ebx, %eax
> + adcl $0, %eax
> + inc %esi
> + testl $2, %esi
> + jz 10b
Now that is grossly inefficient ;-) since you can save one instruction by
moving roll after adcl (hand edited partial patch hunk, won't apply):
+25:
+ testl $1, %esi
+ jz 30f
+ # buf is odd
+ dec %ecx
+ jl 90f
+ movzbl (%esi), %ebx
+ addl %ebx, %eax
+ adcl $0, %eax
+ inc %esi
+ roll $8, %eax
+ testl $2, %esi
+ jz 10b
Gabriel.
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This archive was generated by hypermail 2b29 : Sat Sep 07 2002 - 22:00:24 EST