So nothing fancy?
I am going to wait for a while in case someone comes up with a usage of LEA I can't think of.
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Question
x86 - LEA
This has been puzzling me for a while - of what use is the LEA instruction?
To me it just looks like a MOV instruction which can take a relatively-complex second argument - nothing that can't be done with a MOV, a MUL and an ADD. I know (I think) it was created for loading table/array offsets with indices, but what makes it worth the trouble of implementing, except for conforming to a CISC architecture that is already very complex?
I know it's fast - lea eax, [8*eax+eax] is better than a mul eax, 9, but are there any special 'LEA' tricks?
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Answers
LEA comes for "free", the address calculation pipeline already does this exact kind of thing, so why not make its results available as a separate instruction? And it's a fast instruction, compared to MUL which used to take dozens of cycles.
Another good thing about LEA is it doesnt affect the flags. So you can do multiple-precision arithmetic and calculate the next address without having to push/pop flags.
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by: dimitryPosted on 2005-02-18 at 01:42:07ID: 13343788
You've actually described very well its purpose.
It is in x86 assembler to load table, array r whatever address to register, but also can be used "in tricky" way to make arithmetic
calcultions, like multiplication...