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Probably a silly question.

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What's the xmmword means in IDA Pro?

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XMMWORD is a 128-bit operand for SSE (previously MMX) instructions (it is nothing special in IDA Pro).

It is derived from names of XMM registers (XMM0, XMM1, ...) used with SSE instructions.

  • SSE means “Streaming SIMD Extensions”, where

  • SIMD means “Single Instruction Multiple Data”.

    (Single Instruction - for example addition – is performed on Multiple Data - for example on multiple pairs of numbers.)

(SSE = SIMD + Floating Point Arithmetic + Saturation Arithmetic + Special Instructions)

For explanation:

  • Beside “basic”, well-known instructions (e.g. ADD or JMP) inherited from early Intel X86 instruction set, there is other instruction set (containing e.g. MAXPS or MOVNTQ instructions):

    • SSE (previously MMX – officially a meaningless acronym, often interpreted as MultiMedia eXtension) with their own special set of 128-bit registers (XMM0, XMM1, ... ),
      further extended to

    • AVX (Advanced Vector eXtensions) with added

      • 256-bit YMM registers (YMM0, YMM1, ... – lower halves overlap with XMM registers), and

      • 512-bit ZMM registers (ZMM0, ZMM1, ... – lower halves overlap with YMM registers).

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