mdw@git.distorted.org.uk Git - ssr/blob - StraySrc/Libraries/Sapphire/s/sqrt

   1 ;
   2 ; sqrt.s
   3 ;
   4 ; Fast square root routines
   5 ;
   6 ; © 1995-1998 Straylight
   7 ;
   8
   9 ;----- Licensing note -------------------------------------------------------
  10 ;
  11 ; This file is part of Straylight's Sapphire library.
  12 ;
  13 ; Sapphire is free software; you can redistribute it and/or modify
  14 ; it under the terms of the GNU General Public License as published by
  15 ; the Free Software Foundation; either version 2, or (at your option)
  16 ; any later version.
  17 ;
  18 ; Sapphire is distributed in the hope that it will be useful,
  19 ; but WITHOUT ANY WARRANTY; without even the implied warranty of
  20 ; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  21 ; GNU General Public License for more details.
  22 ;
  23 ; You should have received a copy of the GNU General Public License
  24 ; along with Sapphire.  If not, write to the Free Software Foundation,
  25 ; 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  26
  27 ;----- Standard header ------------------------------------------------------
  28
  29                 GET     libs:header
  30                 GET     libs:swis
  31
  32                 GET     libs:stream
  33
  34 ;----- Main code ------------------------------------------------------------
  35
  36                 AREA    |Sapphire$$Code|,CODE,READONLY
  37
  38 ; --- sqrt ---
  39 ;
  40 ; On entry:     R0 == value to square-root
  41 ;
  42 ; On exit:      R0 == the result
  43 ;
  44 ; Use:          Evaluates the square root of the number given.  This routine
  45 ;               is constructed from the information supplied by David Seal,
  46 ;               and is *extremely* fast.
  47
  48                 EXPORT  sqrt
  49 sqrt            ROUT
  50
  51                 STMFD   R13!,{R1-R4,R14}        ;Stack registers
  52                 MOV     R1,#0                   ;Result so far
  53                 MOV     R2,#0                   ;Current remainder
  54                 MOV     R3,#1                   ;A '01' pair
  55                 MOV     R4,#3                   ;A nice mask
  56
  57                 GBLA    count
  58 count           SETA    0                       ;Start the count at 30
  59
  60                 WHILE   count<=28               ;Set up the loop condition
  61
  62                 AND     R14,R4,R0,LSR #30-count
  63                 ORR     R2,R14,R2,LSL #2
  64                 ORR     R14,R3,R1,LSL #2
  65                 CMP     R2,R14
  66                 ADC     R1,R1,R1
  67                 SUBCS   R2,R2,R14
  68
  69 count           SETA    count+2
  70
  71                 WEND
  72
  73                 AND     R14,R4,R0
  74                 ORR     R2,R14,R2,LSL #2
  75                 ORR     R14,R3,R1,LSL #2
  76                 CMP     R2,R14
  77                 ADC     R1,R1,R1
  78                 SUBCS   R2,R2,R14
  79
  80 c               MOV     R0,R1                   ;Put the result in R0
  81                 LDMFD   R13!,{R1-R4,PC}^        ;Return to caller
  82
  83                 LTORG
  84
  85 ;----- That's all, folks ----------------------------------------------------
  86
  87                 END