Le 09/11/2016 à 20:39, Richard Henderson a écrit :
> On 11/09/2016 07:47 PM, Richard Henderson wrote:
>> On 11/09/2016 06:30 PM, Laurent Vivier wrote:
>>> + /* create [src:X:..] */
>>> +
>>> + tcg_gen_deposit_i32(t0, QREG_CC_X, src, 1, size);
>>> + tcg_gen_shli_i32(t0, t0, 31 - size);
>>> +
>>> + /* rotate */
>>> +
>>> + tcg_gen_rotl_i32(t0, t0, shift);
>>> +
>>> + /* result is [src:..:src:X] */
>>> +
>>> + tcg_gen_andi_i32(X, t0, 1);
>>> + tcg_gen_shri_i32(t0, t0, 1);
>>
>> I don't see how this is supposed to work. If you form [src:x:...],
>> and rotate
>> by 0, then X gets garbage. Of course, you're actually forming
The result is ignored in the case of a rotate by 0 (see movcond in
rotate_reg()).
>> [0:src:x]. But
>> for a rol of 2, the lsb of src gets 0's instead of the msb of src.
for a rol of 2 on an 8bit value [12345678]:
tcg_gen_deposit_i32(t0, QREG_CC_X, src, 1, size);
tcg_gen_shli_i32(t0, t0, 31 - size);
t0 = [12345678x00000000000000000000000]
tcg_gen_rotl_i32(t0, t0, shift);
t0 = [345678x0000000000000000000000012]
tcg_gen_andi_i32(X, t0, 1);
X = 2
tcg_gen_shri_i32(t0, t0, 1);
t0 = [0345678x000000000000000000000001]
tcg_gen_shri_i32(t1, t0, 31 - size);
t1 = [000000000000000000000000345678x0]
tcg_gen_or_i32(dest, t0, t1);
dest = [0345678x0000000000000000345678x1]
-> we keep only 8 bits: [345678x1]
Where am I wrong?
> Feh, actually that only works for rot8, since you need 2*size+1 bits
> available for this. Why not just use shifts. Something like
>
> int shl = shift % 17;
> int shr = shl ^ (size - 1);
> int shx = shl ? shl - 1 : 16;
>
> res32 = (data << shl) | (data >> shr) | (x << shx);
> x = (res32 >> 16) & 1;
If you think it is better, I can do like that.
Thanks,
Laurent
