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| author | Kartik Agaram <vc@akkartik.com> | 2018-09-07 22:13:10 -0700 |
|---|---|---|
| committer | Kartik Agaram <vc@akkartik.com> | 2018-09-07 22:19:13 -0700 |
| commit | e07a3f2886b117970b3cd58f7cd6806cbfe5cc4a (patch) | |
| tree | 6fcddb741f3b15eaa7892b5ce0468a6f3695005a /subx/014indirect_addressing.cc | |
| parent | 608a7fa8d0faf9a3e3d182d9eabe969804443aab (diff) | |
| download | mu-e07a3f2886b117970b3cd58f7cd6806cbfe5cc4a.tar.gz | |
4537
Streamline the factorial function; we don't need to save a stack variable into a register before operating on it. All instructions can take a stack variable directly. In the process we found two bugs: a) Opcode f7 was not implemented correctly. It was internally consistent but I'd never validated it against a natively running program. Turns out it encodes multiple instructions, not just 'not'. b) The way we look up imm32 operands was sometimes reading them before disp8/disp32 operands.
Diffstat (limited to 'subx/014indirect_addressing.cc')
| -rw-r--r-- | subx/014indirect_addressing.cc | 9 |
1 files changed, 5 insertions, 4 deletions
diff --git a/subx/014indirect_addressing.cc b/subx/014indirect_addressing.cc index 344da8de..22a3c179 100644 --- a/subx/014indirect_addressing.cc +++ b/subx/014indirect_addressing.cc @@ -227,16 +227,17 @@ case 0x33: { // xor r/m32 with r32 //:: not -:(scenario not_r32_with_mem_at_r32) +:(scenario not_of_mem_at_r32) % Reg[EBX].i = 0x60; == 0x1 # code segment # op ModR/M SIB displacement immediate - f7 03 # negate *EBX -# ModR/M in binary: 00 (indirect mode) 000 (unused) 011 (dest EBX) + f7 13 # negate *EBX +# ModR/M in binary: 00 (indirect mode) 010 (subop not) 011 (dest EBX) == 0x60 # data segment ff 00 0f 0f # 0x0f0f00ff -+run: 'not' of r/m32 ++run: operate on r/m32 +run: effective address is 0x60 (EBX) ++run: subop: not +run: storing 0xf0f0ff00 //:: compare (cmp) |