Re: [PATCH 07/33] target/ppc: Implement cntlzdm

[Richard Henderson]

On 10/21/21 12:45 PM, matheus.ferst@eldorado.org.br wrote:
> +uint64_t helper_CNTLZDM(uint64_t src, uint64_t mask)
> +{
> +    uint64_t sel_bit, count = 0;
> +
> +    while (mask != 0) {
> +        sel_bit = 0x8000000000000000ULL >> clz64(mask);
> +
> +        if (src & sel_bit) {
> +            break;
> +        }

We need to count how many mask are set left of mask & src.
How about

    sh = clz64(src & mask);
    if (sh == 0) {
        return 0;
    }
    return ctpop64(mask >> (64 - sh));

which could probably be implemented inline relatively easy.

> +static bool trans_CNTLZDM(DisasContext *ctx, arg_X *a)
> +{
> +    REQUIRE_64BIT(ctx);
> +    REQUIRE_INSNS_FLAGS2(ctx, ISA310);
> +#if defined(TARGET_PPC64)
> +    gen_helper_CNTLZDM(cpu_gpr[a->ra], cpu_gpr[a->rt], cpu_gpr[a->rb]);
> +#else
> +    qemu_build_not_reached();
> +#endif
> +    return true;
> +}

Why the ifdef here?  Oh, I see. You could just use target_long in the helper to avoid 
that.  And if not, you should move the helper into an ifdef too.


r~