Post by thread:A Multiply Routine

Dear pic guru's: I've been struggling with this multiply routine, and I think that I've got it working now. It should take an unsigned 24 bit integer value and multiply it by an unsigned 24 bit floating point value with the result being a 24 bit integer. I still think that I need to limit the number of right shifts that it performs in the end, but I haven't thought of any clever ways to do this yet. This is kind of a specialize multiply, but I thought that I would post it to see if anyone can find some mistakes or make use of it. Please inform me of any errors! Oh yeah, It also makes use of a 24 bit integer addition routine. Any critiques will be greatly appreciated. Take care, Derrick Early (still a rookie) ================================================================================ === F_mpy ; 24 bit integer * 24 bit floating point = 24 bit integer ; a*b*2^b3 -> d ; Where a is made up of a1 a2 and a3. b is (b1 b2) * 2^b3. ; And, d is d1 d2 d3. If d overflows to the left, then the ; _overflow bit will be set. clrf d1 clrf d2 clrf d3 bcf _overflow movlw d'16' movwf temp do_temp_gt_0 btfsc b1,7 call add_a_to_d btfsc _overflow goto done_F_mpy bcf _carry rlf b2 rlf b1 incf b3,f bcf _carry rrf a1 rrf a2 rrf a3 while_temp_gt_0 decfsz temp ; while (temp>0) goto do_temp_gt_0 end_temp_gt_0 decf b3,f ; Shift the result in d to an integer value. btfss b3,7 goto shift_left shift_right btfsc _z goto done_F_mpy bcf _carry rrf d1 rrf d2 rrf d3 incf b3,f goto shift_right shift_left btfsc _z goto done_F_mpy bcf _carry rlf d3 rlf d2 rlf d1 decf b3,f btfss _carry goto shift_left bsf _overflow done_F_mpy return add_a_to_d ; a+d -> d this is a 24 bit addition routine bcf _overflow movf a3,w addwf d3,f btfss _carry goto add_byte_2 incfsz d2,same goto add_byte_2 incfsz d1,same goto add_byte_2 bsf _overflow add_byte_2 movf a2,w addwf d2,f btfss _carry goto add_byte_1 incfsz d1,same goto add_byte_1 bsf _overflow add_byte_1 movf a1,w addwf d1,f btfsc _carry bsf _overflow return