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(nasm.info)Section B.4.207

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B.4.207. `PCMPxx': Compare Packed Integers.
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     PCMPEQB mm1,mm2/m64           ; 0F 74 /r             [PENT,MMX]
     PCMPEQW mm1,mm2/m64           ; 0F 75 /r             [PENT,MMX]
     PCMPEQD mm1,mm2/m64           ; 0F 76 /r             [PENT,MMX]

     PCMPGTB mm1,mm2/m64           ; 0F 64 /r             [PENT,MMX]
     PCMPGTW mm1,mm2/m64           ; 0F 65 /r             [PENT,MMX]
     PCMPGTD mm1,mm2/m64           ; 0F 66 /r             [PENT,MMX]

     PCMPEQB xmm1,xmm2/m128        ; 66 0F 74 /r     [WILLAMETTE,SSE2]
     PCMPEQW xmm1,xmm2/m128        ; 66 0F 75 /r     [WILLAMETTE,SSE2]
     PCMPEQD xmm1,xmm2/m128        ; 66 0F 76 /r     [WILLAMETTE,SSE2]

     PCMPGTB xmm1,xmm2/m128        ; 66 0F 64 /r     [WILLAMETTE,SSE2]
     PCMPGTW xmm1,xmm2/m128        ; 66 0F 65 /r     [WILLAMETTE,SSE2]
     PCMPGTD xmm1,xmm2/m128        ; 66 0F 66 /r     [WILLAMETTE,SSE2]

   The `PCMPxx' instructions all treat their operands as vectors of
bytes, words, or doublewords; corresponding elements of the source and
destination are compared, and the corresponding element of the
destination (first) operand is set to all zeros or all ones depending
on the result of the comparison.

   * `PCMPxxB' treats the operands as vectors of bytes;

   * `PCMPxxW' treats the operands as vectors of words;

   * `PCMPxxD' treats the operands as vectors of doublewords;

   * `PCMPEQx' sets the corresponding element of the destination
     operand to all ones if the two elements compared are equal;

   * `PCMPGTx' sets the destination element to all ones if the element
     of the first (destination) operand is greater (treated as a signed
     integer) than that of the second (source) operand.