flat assembler
Message board for the users of flat assembler.
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> Main > Prefix codes |
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MazeGen 25 Jul 2005, 18:58
They are, of course, needed also in 32-bit mode. For instance, prefix 0x66 is needed almost always when you use 16-bit register operands.
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25 Jul 2005, 18:58 |
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The_CodeMaster 25 Jul 2005, 19:55
Ah, yes, 16 & 32 operands have the same opcode, didn't notice it earlier. Thx anyway.
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25 Jul 2005, 19:55 |
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decard 25 Jul 2005, 20:25
some SSE instructions require 66h preffix as well...
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25 Jul 2005, 20:25 |
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The_CodeMaster 25 Jul 2005, 21:35
I know, they are also used to perform string copying requiring 1 instruction (Have IA manuals), though I try to avoid them since I read somwhere that longer instuctions require more time to be prefetched by the instuction decoder.
The IA manual also says that using prefixes won't guaranty the same performance. |
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25 Jul 2005, 21:35 |
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MazeGen 25 Jul 2005, 21:58
The_CodeMaster wrote: I know, they are also used to perform string copying requiring 1 instruction (Have IA manuals) What exactly do you mean? |
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25 Jul 2005, 21:58 |
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Ancient One 26 Jul 2005, 01:51
maybe he means the 'rep' prefix
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26 Jul 2005, 01:51 |
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