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Within these pages, you can find many useful pieces of code mostly in assembly for the Microchip PIC micro controller family. A lot of people have spend many hours trying to put the bits and bytes together. If the code is NOT written by a member of the PCB Heaven community, then a link will be added above the code with the original website that this code was found.
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View code
32 bit integer
Author: Scott Dattalo
This code was originally located @ http://www.piclist.com
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;=========================================================================
; brSQRT32
;
; Calculates the square root of a thirtytwo bit number using the
; binary restoring method.
;
; Result in ACCaHI:ACCaLO
; Mask in ACCbHI:ACCbLO
; Input in ACCcHI:ACCcLO:ACCdHI:ACCdLO
;
; Takes between 392 and 439 cycles (incl. call and return).
; Uses 58 words ROM, 8 bytes RAM including 4 holding the input.
;
;-------------------------------------------------------------------------
brSQRT32:
movlw 0x40 ; Initial value for Result is...
movwf ACCaHI ; ... 01000000 00000000
clrf ACCaLO,f ;
movlw 0xC0 ; Initial value for mask is...
movwf ACCbHI ; ... 11000000 00000000
clrf ACCbLO,f ; (second '1' is loop counter).
Sub_Cmp:movfp ACCaLO,WREG ; Compare root-so-far with current
subwf ACCcLO,f ; ... remainder.
movfp ACCaHI,WREG ;
subwfb ACCcHI,f ;
btfss ALUSTA,C ;
goto brstr ; (result is -ve, need to restore).
In1: movfp ACCbLO,WREG ; set the current bit in the result.
iorwf ACCaLO,f ;
movfp ACCbHI,WREG ;
iorwf ACCaHI,f ;
ShftUp: rlcf ACCdLO,f ;
rlcf ACCdHI,f ;
rlcf ACCcLO,f ;
rlcf ACCcHI,f ;
rrcf ACCbHI,f ; Shift mask right for next bit, whilst
rrcf ACCbLO,f ; ... shifting IN MSB from remainder.
btfsc ACCbHI,7 ; If MSB is set, unconditionally set the
goto USet1 ; ... next bit.
movfp ACCbLO,WREG ; Append '01' to root-so-far
xorwf ACCaLO,f ;
movfp ACCbHI,WREG ;
xorwf ACCaHI,f ;
btfss ALUSTA,C ; If second '1' in mask is shifted out,
goto Sub_Cmp ; ... then that was the last normal iteration.
movfp ACCaLO,WREG ; Last bit Generation.
subwf ACCcLO,f ; ... The final subtract is 17-bit (15-bit root
movfp ACCaHI,WREG ; ... plus '01'). Subtract 16-bits: if result
subwfb ACCcHI,f ; ... generates a carry, last bit is 0.
btfss ALUSTA,C ;
return
movlw 1 ; If result is 0 AND msb of is '0', result bit
btfsc ALUSTA,Z ; ... is 0, otherwise '1'.
btfsc ACCdHI,7 ;
xorwf ACCaLO,f ;
return
USet1: btfsc ALUSTA,C ; If mask has shifted out, leave. final bit
return ; ... has been set by iorwf at in1.
bcf ACCbHI,7 ; clear bit shifted in from input.
movfp ACCbLO,WREG ; Append '01' to root-so-far
xorwf ACCaLO,f ;
movfp ACCbHI,WREG ;
xorwf ACCaHI,f ;
movfp ACCaLO,WREG ; This subtraction is guaranteed not to
subwf ACCcLO,f ; ... cause a borrow, so subtract and
movfp ACCaHI,WREG ; ... jump back to insert a '1' in the
subwfb ACCcHI,f ; ... root.
goto In1 ;
brstr: movfp ACCaLO,WREG ; A subtract above at Sub_Cmp was -ve, so
addwf ACCcLO,f ; ... restore the remainder by adding.
movfp ACCaHI,WREG ; The current bit of the root is zero.
addwfc ACCcHI,f ;
goto ShftUp ; |
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