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(as.info)i386-SIMD

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Intel's MMX and AMD's 3DNow! SIMD Operations
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   `as' supports Intel's MMX instruction set (SIMD instructions for
integer data), available on Intel's Pentium MMX processors and Pentium
II processors, AMD's K6 and K6-2 processors, Cyrix' M2 processor, and
probably others.  It also supports AMD's 3DNow!  instruction set (SIMD
instructions for 32-bit floating point data) available on AMD's K6-2
processor and possibly others in the future.

   Currently, `as' does not support Intel's floating point SIMD, Katmai
(KNI).

   The eight 64-bit MMX operands, also used by 3DNow!, are called
`%mm0', `%mm1', ... `%mm7'.  They contain eight 8-bit integers, four
16-bit integers, two 32-bit integers, one 64-bit integer, or two 32-bit
floating point values.  The MMX registers cannot be used at the same
time as the floating point stack.

   See Intel and AMD documentation, keeping in mind that the operand
order in instructions is reversed from the Intel syntax.