Richard Henderson <[email protected]> writes:
> On 07/18/2016 10:35 PM, Nikunj A Dadhania wrote:
>> + tcg_gen_andi_tl(src1, cpu_gpr[rA(ctx->opcode)], 0xFF);
>> + for (i = 0; i < 64; i += 8) {
>> + tcg_gen_shri_tl(t0, arg1, i);
>> + tcg_gen_andi_tl(t0, t0, 0xFF);
>> + tcg_gen_brcond_tl(TCG_COND_EQ, src1, t0, l1);
>> + }
>> + tcg_gen_movi_i32(cpu_crf[crfD(ctx->opcode)], 0);
>> + tcg_gen_br(l2);
>> + gen_set_label(l1);
>> + /* Set match bit, i.e. CRF_GT */
>> + tcg_gen_movi_i32(cpu_crf[crfD(ctx->opcode)], 1 << CRF_GT);
>
> Ew. This can be done much better as
>
> http://graphics.stanford.edu/~seander/bithacks.html#ZeroInWord
>
> Which still might be best done in a helper, because of the constants involved
> (tcg is not nearly so good as gcc in building full 64-bit constants).
>
> C.f. target-alpha/int_helper.c, helper_cmpbe0 (which computes different
> information than cmpeqb, but is still helpful as an example).
Thanks for the hints, that got reduce to following:
#define haszero(v) (((v) - 0x0101010101010101UL) & ~(v) & 0x8080808080808080UL)
#define hasvalue(x,n) (haszero((x) ^ (~0UL/255 * (n))))
uint32_t helper_cmpeqb(target_ulong ra, target_ulong rb)
{
return !!hasvalue(rb, ra);
}
Regards
Nikunj
