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/* -*- Mode: Asm -*- */
/* Copyright (c) 2002 Michael Stumpf <mistumpf@de.pepperl-fuchs.com>
All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:
* Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
* Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in
the documentation and/or other materials provided with the
distribution.
* Neither the name of the copyright holders nor the names of
contributors may be used to endorse or promote products derived
from this software without specific prior written permission.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.
*/
/*
sqrt.S is part of FPlib V 0.3.0 ported to avr-as
for details see readme.fplib
*----------------------------------------------------------------------------------------
*
* A = sqrt(A)
*/
#include "gasava.inc"
#include "fplib.inc"
TEXT_SEG(fplib, sqrt)
FUNCTION(sqrt)
GLOBAL(sqrt)
SBRC rA3,7
RJMP _U(__fp_nanEDOM) ; sign bit is set -> argument range error
/* A = sign(=0):(exp+7F):[1].mant = 2^(exp)*1.mant
* = (LSB(exp)+7F) + (exp>>1) + (exp>>1):[1].mant = (2^(exp>>1))^2 * 2^(LSB(exp))*1.mant
* = 2^(exp>>1)^2 * A'
* A' = [2^0*1.0... 2^1*1.1111111] = [1.0...4.0[
*
* sqrt(A) = 2^(exp>>1) * sqrt( A' )
* sqrt(A') = [1.0...2.0[ -> result of srqt(A') has definetely exponent 7F! -> exp(X0) = 7F
*
* the matissa of X0 is taken as ( 0.mant >> 1 ) 0.0mant
* plus if LSB(exp)==1 [LSB(exp-7F)==0] 0.100000
* plus the implicit one 1.000000
*/
MOV rB2,rA2 ; needed later on
TST rA3
BREQ _sqrt_ZERO ; sqrt(0) = 0
RCALL _U(__fp_split1) ; does not return on NaN
_sqrt_00:
MOV rTI0,rA3
SUBI rTI0,0x7F
ASR rTI0 ; this is dExp!
SUB rA3,rTI0
SUB rA3,rTI0
PUSH rTI0 ; exponent offset
SUBI rB2,0x80 ; == EOR 0x80
ROR rB2
CLR rB1 ; a slightly smaller X(0) than the calculated is better
CLR rB0 ; and saves 2 right shifts
ORI rB2,0x80 ; implicit one
LDI rB3,0x7F ; load exponent 7F
CLT ; clears T
PUSH rS0
PUSH rS1
PUSH rS2
PUSH rS3 ; rS3::rS0 = Abak
PUSH rS4
PUSH rS5
PUSH rS6
PUSH rS7 ; rS7::rS4 = Bbak
MOV rS3,rA3
MOV rS2,rA2
MOV rS1,rA1
MOV rS0,rA0 ; Abak = A
_sqrt_10:
MOV rA0,rS0 ;
MOV rA1,rS1 ;
MOV rA2,rS2 ;
MOV rA3,rS3 ; A = Abak
MOV rS7,rB3
MOV rS6,rB2
MOV rS5,rB1
MOV rS4,rB0 ; Bbak = B
; divsf3x does not need preset rAE,rBE
RCALL _U(__divsf3x) ; FP1X = arg/xn
; now rAE = rBE = 0 or 80 or 0xFF ,ok for addsf3x
MOV rB3,rS7
MOV rB2,rS6
MOV rB1,rS5
MOV rB0,rS4 ; B = Bbak
CLR rT1c ; addx uses R1.7 as sign
RCALL _U(__addsf3x) ; FP1X = arg/xn + xn
DEC rA3 ; div by 2 := Xn+1
MOV rB3,rA3
MOV rB2,rA2
MOV rB1,rA1
MOV rB0,rA0 ;
CP rS4,rB0 ;
CPC rS5,rB1 ;
CPC rS6,rB2
CPC rS7,rB3 ; cmp B to Bbak
BRNE _sqrt_10
POP rS7
POP rS6
POP rS5
POP rS4
POP rS3
POP rS2
POP rS1
POP rS0
POP rT0
ADD rA3,rT0 ;
_sqrt_100:
CLR rT0 ; no rounding beyond rAE
RJMP _U(__fp_merge)
_sqrt_ZERO:
RET
ENDFUNC
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