Hello,

I've created a routine for a 24 bit signed compare. 6 byte variables
mpos0..2 and wpos0..2 are compared and at the end the result is in two bits;
pos_equal  (if set pos_sign has no use)
pos_sign.

I was wandering if anybody has a faster (and/or shorter) routine for this
logic-problem.

My code:

  bcf   pos_equal           // assume not equal; set '0'
  bsf   pos_sign            // assume wpos>mpos; set '1'

  movf  wpos2,w             // check sign bits to see if one is positive..
  xorwf mpos2,w             // ..and the other negative or visa versa
  andlw 0x80                // only look at sign result
  btfsc 03,2                // if set ->zero=0, skip next
  goto  nosign

  btfsc wpos2,7             // wpos negative? skip if not
  bcf   pos_sign            // yes, so wpos<mpos
  goto  cmpdone             // we're finished

  nosign:                   // no sign difference, we've to compare
  movf  mpos2,W
  subwf wpos2,w             // w=wpos2-mpos2
  btfss 03,2                // if equal, skip next
  goto  cmpdone

  movf  mpos1,w
  subwf wpos1,w             // w=wpos1-mpos1
  btfss 03,2                // if equal, skip next
  goto  cmpdone

  movf  mpos0,w
  subwf wpos0,w             // w=wpos1-mpos1
  btfsc 03,2                // check zero bit skip if clear
  bsf   pos_equal           // set equal bit

  cmpdone:
  btfss 03,0                // carry flag = '1' ?
  bcf   pos_sign            // no; so clear pos_sign
  cmpexit:

Edwin Baaij  (Electronics Engineer)
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University of Amsterdam                 phone:  +31-20-5256346
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Valckenierstraat 65-67                  e-mail: baaij@phys.uva.nl
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