Re: [Qemu-devel] [PATCH 16/25] tcg/i386: Handle ctz and clz opcodes

[Bastian Koppelmann]

On 11/16/2016 08:25 PM, Richard Henderson wrote:
> +
> +    OP_32_64(clz):
> +        if (const_args[2]) {
> +            tcg_debug_assert(have_bmi1);
> +            tcg_debug_assert(args[2] == (rexw ? 64 : 32));
> +            tcg_out_modrm(s, OPC_LZCNT + rexw, args[0], args[1]);
> +        } else {
> +            /* ??? See above.  */
> +            tcg_out_modrm(s, OPC_BSR + rexw, args[0], args[1]);

The Intel ISA manual states that it find the bit index of the most
significant bit, where the least significant bit is index 0. So for the
input 0x2 this should return 1. However this is not the number of
leading zeros.

Cheers,
    Bastian