Request for reviews (L): 6823354: Add intrinsics for{Integer,Long}.{numberOfLeadingZeros,numberOfTrailingZeros}()

[Christian Thalinger]

On Thu, 2009-04-23 at 09:57 -0700, Vladimir Kozlov wrote:
> "TEMP dst" is not needed in countLeadingZerosI_bsr (32- and 64-bit .ad)
> since the code will work even if src and dst registers are the same.

Ahh, right.

> 
> The same in countLeadingZerosL_bsr in x86_64.ad, in x86_32.ad
> it is not needed in countTrailingZerosI.

Yes.

> 
> x86_32.ad:
> 
> You can avoid tmp register in countLeadingZerosL:
> 
> +   format %{ "LZCNT  $dst, $src.hi\t# count leading zeros (long)\n\t"
> +             "JNC    done\n\t"
> +             "LZCNT  $dst, $src.lo\n\t"
> +             "ADD    $dst, 32\n"
> +       "done:" %}
> 
> and in countLeadingZerosL_bsr:
> 
> +   format %{ "BSR    $dst, $src.hi\t# count leading zeros (long)\n\t"
> +             "JZ     msw_is_zero\n\t"
> +             "ADD    $dst, 32\n\t"
> +             "JMP    not_zero\n"
> +       "msw_is_zero:\n\t"
> +             "BSR    $dst, $src.lo\n\t"
> +             "JNZ    not_zero\n\t"
> +             "MOV    $dst, -1\n"
> +       "not_zero:\n\t"
> +             "NEG    $dst\n\t"
> +             "ADD    $dst, 63\n" %}
> 
> and in countTrailingZerosL:
> 
> +   format %{ "BSF    $dst, $src.lo\t# count trailing zeros (long)\n\t"
> +             "JNZ    done\n\t"
> +             "BSF    $dst, $src.hi\n\t"
> +             "JNZ    skip\n\t"
> +             "MOV    $dst, 32\n"
> +       "skip:\n\t"
> +             "ADD    $dst, 32\n"
> +       "done:" %}

These are good ones!  Thanks!

> 
> 
> Could you also run your benchmark again to see if performance is changed.

I will.

-- Christian