Combining prefixes in SSE
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by Nathan Fellman
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Published on 2010-03-08T20:09:34Z
Indexed on
2010/03/09
11:51 UTC
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In SSE the prefixes 066h (operand size override) 0F2H (REPNE) and 0F3h (REPE) are part of the opcode.
In non-SSE 066h switches between 32-bit (or 64-bit) and 16-bit operation. 0F2h and 0F3h are used for string operations. They can be combined so that 066h and 0F2h (or 0F3h) can be used in the same instruction, because this is meaningful. What is the behavior in an SSE instruction? For instance, we have (ignoring mod/rm for now):
0f 58 --> addps
66 0f 58 --> addpd
f2 0f 58 --> addsd
f3 0f 58 --> addss
But what is this?
66 f2 0f 58
And how about?
f2 66 0f 58
Not to mention the following which has two conflicting REP prefixes:
f2 f3 0f 58
What is the spec for thse?
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