std::pow implementation

[Steven Bosscher]

Op di 29-07-2003, om 14:55 schreef Richard Guenther:
> double foo2(double x)
> {
>   pow(x, 2);
> }
> 
> gets to (with gcc3.4, __cmath_power declared inline, -O2 -funroll-loops
> -ffast-math)
> 
> _Z4foo2d:
> .LFB12:
>         pushl   %ebp    #
> .LCFI4:
>         movl    %esp, %ebp      #,
> .LCFI5:
>         fldl    8(%ebp) # x
>         fld1
>         movl    $1, %eax        #, __n
>         jmp     .L62    #
>         .p2align 4,,7
> .L73:
>         fxch    %st(1)  #
> .L62:
>         fxch    %st(1)  #
>         testb   $1, %al #, __n
>         fmul    %st(0), %st     #,
>         je      .L59    #,
>         fmul    %st, %st(1)     #,
> .L59:
>         shrl    %eax    # __n
>         jne     .L73    #,
>         fstp    %st(0)  #
>         popl    %ebp    #
>         ret
> 
> yay!

Not that it didn't even unroll the loop at all.

I have no idea if it makes any difference, I'm just curious: What
happens if you replace 

      while (__n >>= 1)

with
      while (__n = __n / 2)
?

Maybe the loop stuff can't handle shifts...

Gr.
Steven