A strange bit of code in MacroAssembler::multiply_128_x_128_loop

[Andrew Haley]

On 04/10/2015 05:30 PM, Vladimir Kozlov wrote:
> It restores counter after:
> 
>    subl(idx, 2);
>    jcc(Assembler::negative, L_check_1);
> 
> The value could be 1,2,3 before this point (idx & 3 before).
> After 'sub 2': -1, 0, 1.
> 
> So we have to restore to positive values before subtracting 1.

But after

>    andl (idx, 0x1);

the only possible values are 0 and 1, and this is true regardless of the
'sub 2'.

>>>    addl (idx, 0x2);
>>>    andl (idx, 0x1);
>>>    subl(idx, 1);
>>>    jcc(Assembler::negative, L_post_third_loop_done);

Andrew.