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|
;--------------------------------------------------------------------------
; g_ftoa.S - floating point to ascii conversion
;
; Copyright (C) 2004, George Gallant <ggallant571 AT verizon.net>
;
; This library is free software; you can redistribute it and/or modify it
; under the terms of the GNU General Public License as published by the
; Free Software Foundation; either version 2, or (at your option) any
; later version.
;
; This library is distributed in the hope that it will be useful,
; but WITHOUT ANY WARRANTY; without even the implied warranty of
; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
; GNU General Public License for more details.
;
; You should have received a copy of the GNU General Public License
; along with this library; see the file COPYING. If not, write to the
; Free Software Foundation, 51 Franklin Street, Fifth Floor, Boston,
; MA 02110-1301, USA.
;
; As a special exception, if you link this library with other files,
; some of which are compiled with SDCC, to produce an executable,
; this library does not by itself cause the resulting executable to
; be covered by the GNU General Public License. This exception does
; not however invalidate any other reasons why the executable file
; might be covered by the GNU General Public License.
;--------------------------------------------------------------------------
;--
;
; File: ftoa.asm
; Author: George Gallant
; Date: 19OCT04
;
; This routine provides a floating point to ascii conversion.
; It was written support the SDCC project.
;
; SDCC C Syntax:
;
; extern void g_ftoa(data char *buf, float num, char precision);
;
; The routine is NOT reenterant but expects the entire parameter list
; to be placed on the stack.
;
; Notes: 1. measured 105usec to convert -65535.996 on a 20MHz 18f252
; 2. Software stack can not cross a RAM page boundary
;
;--
list r=dec, n=96, st=off, mm=off
nolist
include <p18fxxx.inc>
list
udata
extern digits
exp: res 1
man: res 4
r: res 5
x: res 3
bp: res 2
prec: res 1
ctr: res 1
code
extern cvt_dec_word
global _g_ftoa
_g_ftoa: movff FSR2H,POSTDEC1
movff FSR2L,POSTDEC1
movff FSR1H,FSR2H
movff FSR1L,FSR2L
movff exp, POSTDEC1
movff man+0, POSTDEC1
movff man+1, POSTDEC1
movff man+2, POSTDEC1
movff man+3, POSTDEC1
movff r+0, POSTDEC1
movff r+1, POSTDEC1
movff r+2, POSTDEC1
movff r+3, POSTDEC1
movff r+4, POSTDEC1
movff x+0, POSTDEC1
movff x+1, POSTDEC1
movff bp+0, POSTDEC1
movff bp+1, POSTDEC1
movff prec, POSTDEC1
movff ctr, POSTDEC1
movff FSR0H,POSTDEC1
movff FSR0L,POSTDEC1
movlw 3
addwf FSR2L, f
btfsc STATUS,C
incf FSR2H, f
movff POSTINC2,FSR0L ;get the low byte of buf pointer
movff POSTINC2,FSR0H
movff POSTINC2,man+0 ;get the low byte of float
movff POSTINC2,man+1
movff POSTINC2,man+2
movff POSTINC2,exp
movff POSTINC2,prec
rlcf man+2,w
rlcf exp,f
bnc @1
movlw '-'
movwf POSTINC0
@1: movff man+0,r+0
movff man+1,r+1
movff man+2,r+2
bsf r+2,7
clrf r+3
clrf r+4
; Shift the mantissa left or right by the expondent
movf exp,w ;get the expondent
sublw 127 ;subtract the bais
bz @4 ;skip shifting if zero
bn @3 ;shift left if neg
@2: bcf STATUS,C ;otherwise, shift right
rrcf r+4,f
rrcf r+3,f
rrcf r+2,f
rrcf r+1,f
rrcf r+0,f
decfsz WREG,w
bra @2
bra @4
@3: bcf STATUS,C
rlcf r+0, f
rlcf r+1, f
rlcf r+2, f
rlcf r+3, f
rlcf r+4, f
incfsz WREG,w
bra @3
@4: rlcf r+2,w ;extract bit 23
rlcf r+3,f ;shift rest of whole number
rlcf r+4,f
movff r+3,PRODL
movff r+4,PRODH
call cvt_dec_word
movlw '.'
movwf POSTINC0
@10: movlw 0x7F
andwf r+2,f
clrf r+3
movff r+0,x+0 ;temp copy
movff r+1,x+1
movff r+2,x+2
bcf STATUS,C ;mult by 2
rlcf r+0,f
rlcf r+1,f
rlcf r+2,f
rlcf r+3,f
bcf STATUS,C ;mult by 4
rlcf r+0,f
rlcf r+1,f
rlcf r+2,f
rlcf r+3,f
movf x+0,w ;mult by 5
addwf r+0,f
movf x+1,w
addwfc r+1,f
movf x+2,w
addwfc r+2,f
movlw 0
addwfc r+3,f
rlcf r+2,w ;div by 0x400000
rlcf r+3,f ;or just extract bits 24-22
rlcf WREG,w
rlcf r+3,f
movf r+3,w ;this is the bcd value
addlw 0x30 ;convert to ascii
movwf POSTINC0 ;and save in memory
bcf STATUS,C ;mult by 2
rlcf r+0,f
rlcf r+1,f
rlcf r+2,f
decfsz prec,f
bra @10
clrf POSTINC0 ;pack a nullbyte at the end
movff ctr, POSTDEC1
movff prec, POSTDEC1
movff bp+1, POSTDEC1
movff bp+0, POSTDEC1
movff x+1, POSTDEC1
movff x+0, POSTDEC1
movff r+4, POSTDEC1
movff r+3, POSTDEC1
movff r+2, POSTDEC1
movff r+1, POSTDEC1
movff r+0, POSTDEC1
movff man+3, POSTDEC1
movff man+2, POSTDEC1
movff man+1, POSTDEC1
movff man+0, POSTDEC1
movff exp, POSTDEC1
movff PREINC1,FSR0L
movff PREINC1,FSR0H
movff PREINC1,FSR2L
movff PREINC1,FSR2H
return
end
|
