From 8f256f1f2ee6a2a49816dd23d26cd120f526bf0b Mon Sep 17 00:00:00 2001 From: Kartik Agaram Date: Fri, 6 Mar 2020 18:31:14 -0800 Subject: 6090 - new instruction: multiply by immediate This is a 3-operand instruction: r32 = rm32 * imm32 It looks like https://c9x.me/x86/html/file_module_x86_id_138.html has a bug, implying the same opcode supports a 2-operand version. I don't see that in the Intel manual pdf, or at alternative sites like https://www.felixcloutier.com/x86/imul Native runs seem to validate my understanding. In the process I also fixed a bug in the existing multiply instruction 0f af: the only flags it sets are OF and CF. The other existing multiply instruction f7 was doing things right. --- 013direct_addressing.cc | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-) (limited to '013direct_addressing.cc') diff --git a/013direct_addressing.cc b/013direct_addressing.cc index 729b4d08..2450e54c 100644 --- a/013direct_addressing.cc +++ b/013direct_addressing.cc @@ -321,10 +321,8 @@ case 0xaf: { // multiply r32 by r/m32 trace(Callstack_depth+1, "run") << "multiply " << rname(arg1) << " by r/m32" << end(); const int32_t* arg2 = effective_address(modrm); int32_t result = Reg[arg1].i * (*arg2); - SF = (Reg[arg1].i < 0); - ZF = (Reg[arg1].i == 0); int64_t full_result = static_cast(Reg[arg1].i) * (*arg2); - OF = (Reg[arg1].i != full_result); + OF = (result != full_result); CF = OF; trace(Callstack_depth+1, "run") << "SF=" << SF << "; ZF=" << ZF << "; CF=" << CF << "; OF=" << OF << end(); Reg[arg1].i = result; -- cgit 1.4.1-2-gfad0