parallel xlat insse2?

Posted on 2004-11-09
Last Modified: 2008-03-06
Dear all,

The xlat instruction is:


Is there a prallel implementaions in SSE2?

xmm1[0] = DWORD PTR[EBX+xmm1[0] ].
xmm1[1] = DWORD PTR[EBX+xmm1[1] ].
xmm1[2] = DWORD PTR[EBX+xmm1[2] ].
xmm1[3] = DWORD PTR[EBX+xmm1[3] ].

THank you.
Question by:hengck23
    1 Comment
    LVL 22

    Accepted Solution

    XLAT is one of those instructions that  got left behind in slow microcode.  It takes FOUR cycles to do ONE byte.

    On a Pentium you can do at least eight times as fast by making a 64K lookup table and doing:

    mov  ax,Table[bx+si]   // where bx is the base address and si has two bytes you want to convert.

    Actually you can do FOUR bytes in one cycle, as the two pipes can each do one of the above instructions per cycle, so that's SIXTEEN times faster than XLAT.

    If that good enough?


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