Re: .../asm-i386/bitops.h performance improvements

From: Mikael Pettersson
Date: Thu Jun 16 2005 - 02:11:49 EST

Bodo Eggert writes:
> My documentation says:
> lea reg16, mem
> Available on 8086, 80186, 80286, 80386, 80486
> 32-bit-extension available
> Opcode: 8D mod reg r/m
> reg will be the target register (AX .. DI), and mod and r/m will select
> something like a direct address, a register or a combination like
> BP+DI+ofs (I won't copy the table). A multiplier is not mentioned there.

You're looking at the wrong parts of the documentation. The 16-bit
mode ModR/M doesn't have SIB, but the 32-bit mode does. The SIB includes
the scaled index. All IA32 processors have it. The only LEA-related
quirk is that its ModR/M must not describe a non-memory operand.
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