[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

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

From: Richard Henderson
Subject: Re: [Qemu-devel] [PATCH 16/25] tcg/i386: Handle ctz and clz opcodes
Date: Thu, 17 Nov 2016 20:53:46 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0

On 11/17/2016 05:50 PM, Bastian Koppelmann wrote:
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.

Oh, of course you're right. I thought I was testing this, but while alpha does have this operation, it turns out it isn't used much.


reply via email to

[Prev in Thread] Current Thread [Next in Thread]