On Thu, Nov 01, 2001 at 10:34:53AM -0500, Richard B. Johnson wrote:
> Well not exactly zealots. I test a lot of stuff. In fact, the code
> you propose:
>
> if(++jiffies==0) jiffies_hi++;
>
> ... actually works quite well:
Uhm, no, it really doesn't. See how it pairs with other instructions and
what the cost is when it doesn't have to be as bad:
this:
unsigned long a, b;
if (++a == 0) b++;
gives:
movl a, %eax
movl %esp, %ebp
incl %eax
testl %eax, %eax
movl %eax, a
je .L3
.L2:
popl %ebp
ret
.p2align 4,,7
.L3:
incl b
jmp .L2
which is really gross considering that:
unsigned long long c;
c++;
gives:
addl $1, c
adcl $0, c+4
which is quite excellent.
-ben
-
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This archive was generated by hypermail 2b29 : Wed Nov 07 2001 - 21:00:15 EST