Here is a debugged version. It is slightly smaller and faster. Thanks to James Hillman [james at indinterface.co.uk] for testing!Final release! :)
;********************************************************************** ;By Nikolai Golovchenko ;24 BIT FLOATING POINT SQARE ROOT ; ;Input: ; AARGB0  high byte with sign bit ; AARGB1  low byte ; AEXP  exponent 2^(AEXP  127) ;Output: ; AARGB01, AEXP  24 bit floating point ;Temporary: ; BARGB01, BEXP  temporary for result ; TEMPB01 ; LOOPCOUNT  counter ; ;ROM: 85 instructions ;RAM: 9 bytes ; ;Timing (includes call and return) ;6 cycles best case ;2+3+18+8*261+8*211+7+2= 406 cycles worst case ;********************************************************************** ;NOTES: 1)Square root is taken on absolute value of the number ; (sign bit is ignored) ; 2)Rounding not implemented yet ;********************************************************************** FPSQRT24 ;Normalize input ;1)Check for zero input  if zero then exit ;2)Change sign to 1 and use sign bit as explicit MSB ;3)Divide BEXP = BEXP / 2 ;4)If AEXP can be divided by 2 (AEXP<0>=1) then ;BARGB1 = 1, AARGB<01> << 1 and find 15 more bits ;5)Else find 16 more bits movf AEXP, w ;if zero input then return btfsc 0x03, 2 retlw 0x00 clrf BARGB0 ;set up all used clrf BARGB1 ;temporary registers clrf TEMPB0 ; clrf TEMPB1 ; bsf AARGB0, 7 ;make MSB explicit and ignore mantissa sign ;sqrt(2^E*M)=2^(E/2)*sqrt(M) ;we will align mantissa point above MSb. This is ;equivalent to division by 2. Or, ;sqrt(2^E*M)=sqrt(M/2)*2^((E+1)/2) ;new exponent is (E+1)/2 ;new mantissa is M/2 (not changed, just new point position) ;divide (bexp+1) by 2. bexp is (eb + 127), where eb=126..128! ;eb/2 is rounded to minus infinity! movwf BEXP ;copy aexp to bexp decf BEXP, f ;ensure required round mode bcf 0x03, 0 ;divide by 2 rrf BEXP, f ; movlw 0x40 ;correct bias after division addwf BEXP, f ; ;if (E+1)/2 result has a remainder, then multiply mantissa by 2 ;(left shift) btfss AEXP, 0 goto FPSQRT24a rlf AARGB1, f ;(carry was zero) rlf AARGB0, f bsf BARGB1, 0 ;set first bit of current result ;and discard MSb of mantissa (we ;used it already by setting first bit) FPSQRT24a ;First find 8 bits of result. This will shift AARGB0  AARGB1 to TEMPB1 ;Then only zeros will be fed instead of AARGB0 movlw 0x08 ;loop counter movwf LOOPCOUNT ; FPSQRT24b movlw 0x40 ;substract test bit from subwf AARGB0, f ;current lowest byte. ;it works also exactly ;like 0xC0 addition for the ;addition branch. movf BARGB1, w ;load accumulator with ;current result LSB btfsc TEMPB0, 7 goto FPSQRT24b_add btfss 0x03, 0 incfsz BARGB1, w subwf TEMPB1, f movlw 0x01 btfss 0x03, 0 subwf TEMPB0, f goto FPSQRT24b_next FPSQRT24b_add btfsc 0x03, 0 incfsz BARGB1, w addwf TEMPB1, f movlw 0x01 btfsc 0x03, 0 addwf TEMPB0, f FPSQRT24b_next rlf BARGB1, f ;shift result into result bytes rlf BARGB0, f rlf AARGB1, f ;Shift out next two bits of input rlf AARGB0, f ; rlf TEMPB1, f ; rlf TEMPB0, f ; rlf AARGB1, f ; rlf AARGB0, f ; rlf TEMPB1, f ; rlf TEMPB0, f ; decfsz LOOPCOUNT, f ;repeat untill 8 bits will be found goto FPSQRT24b ;Find other 7 or 8 bits. Only zeros are fed instead of AARGB0 ;Repeat untill MSb of result gets set FPSQRT24d btfsc BARGB1, 0 ;if Temp sign is positive, than jump to subtraction goto FPSQRT24d_sub ;(previous result bit is inverted sign bit, ;Tempb0.7 can not be used instead, because ;it may overflow) ;after LSBs addition (0x00 + 0xC0 = 0xC0) C=0, ;so we just continue adding higher bytes, ;keeping in mind that LSB=0xC0 and C=0 movf BARGB1, w addwf TEMPB1, f movf BARGB0, w btfsc 0x03, 0 incfsz BARGB0, w addwf TEMPB0, f goto FPSQRT24d_next FPSQRT24d_sub bcf 0x03, 0 ;simulate borrow (0x00  0x40 = 0xC0, C=0) incfsz BARGB1, w subwf TEMPB1, f movf BARGB0, w btfss 0x03, 0 incfsz BARGB0, w subwf TEMPB0, f FPSQRT24d_next rlf BARGB1, f ;shift result into result bytes rlf BARGB0, f bsf 0x03, 0 ;Shift out next two bits of input rlf TEMPB1, f ;(set carry before each shift to rlf TEMPB0, f ;simulate 0xC0 value) bsf 0x03, 0 ; rlf TEMPB1, f ; rlf TEMPB0, f ; btfss BARGB0, 7 ;repeat untill all 16 bits will be found goto FPSQRT24d ;flag C, TEMPB1  TEMPB0 contain current input that may be used to find 17th bit for rounding ;Copy BARG to AARG movf BEXP, w movwf AEXP movf BARGB0, w movwf AARGB0 movf BARGB1, w movwf AARGB1 bcf AARGB0, 7 ;clear sign bit (overwrites explicit MSB, which is always one) retlw 0x00 ;********************************************************************** ;Last updated 21Nov00
Comments:
See also:
file: /Techref/microchip/math/sqrt/fpsqrt24.htm, 6KB, , updated: 2005/11/3 15:24, local time: 2014/9/20 15:16,

©2014 These pages are served without commercial sponsorship. (No popup ads, etc...).Bandwidth abuse increases hosting cost forcing sponsorship or shutdown. This server aggressively defends against automated copying for any reason including offline viewing, duplication, etc... Please respect this requirement and DO NOT RIP THIS SITE. Questions? <A HREF="http://www.piclist.com/techref/microchip/math/sqrt/fpsqrt24.htm"> PIC Microcontoller Math Method 24 Bit Floating Point Square Root</A> 
Did you find what you needed? 
PICList 2014 contributors:
o List host: MIT, Site host massmind.org, Top posters @20140920 RussellMc, Richard R. Pope, IVP, John Gardner, alan.b.pearce, David C Brown, James Cameron, Bob Blick, Josh Koffman, Isaac Marino Bavaresco, * Page Editors: James Newton, David Cary, and YOU! * Roman Black of Black Robotics donates from sales of Linistep stepper controller kits. * Ashley Roll of Digital Nemesis donates from sales of RCL1 RS232 to TTL converters. * Monthly Subscribers: Gregg Rew. ongoing support is MOST appreciated! * Contributors: Richard Seriani, Sr. 
Welcome to www.piclist.com! 
.