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/* -*- Mode: Asm -*- */
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/* Copyright (c) 2002 Michael Stumpf <mistumpf@de.pepperl-fuchs.com>
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Copyright (c) 2006 Anatoly Sokolov <aesok@post.ru>
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Copyright (c) 2006 Dmitry Xmelkov
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Redistribution and use in source and binary forms, with or without
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modification, are permitted provided that the following conditions are met:
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* Redistributions of source code must retain the above copyright
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notice, this list of conditions and the following disclaimer.
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* Redistributions in binary form must reproduce the above copyright
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notice, this list of conditions and the following disclaimer in
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the documentation and/or other materials provided with the
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* Neither the name of the copyright holders nor the names of
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contributors may be used to endorse or promote products derived
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from this software without specific prior written permission.
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INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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POSSIBILITY OF SUCH DAMAGE.
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/* $Id: sqrt.S,v 1.5.2.2 2006/01/20 20:39:28 aesok Exp $ */
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sqrt.S is part of FPlib V 0.3.0 ported to avr-as
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for details see readme.fplib
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*----------------------------------------------------------------------------------------
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POSSIBILITY OF SUCH DAMAGE. */
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/* $Id: sqrt.S,v 1.8 2007/01/14 15:13:10 dmix Exp $ */
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/* double sqrt (double);
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RJMP _U(__fp_nanEDOM) ; sign bit is set -> argument range error
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/* A = sign(=0):(exp+7F):[1].mant = 2^(exp)*1.mant
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* = (LSB(exp)+7F) + (exp>>1) + (exp>>1):[1].mant = (2^(exp>>1))^2 * 2^(LSB(exp))*1.mant
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* A' = [2^0*1.0... 2^1*1.1111111] = [1.0...4.0[
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* sqrt(A) = 2^(exp>>1) * sqrt( A' )
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* sqrt(A') = [1.0...2.0[ -> result of srqt(A') has definetely exponent 7F! -> exp(X0) = 7F
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* the matissa of X0 is taken as ( 0.mant >> 1 ) 0.0mant
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* plus if LSB(exp)==1 [LSB(exp-7F)==0] 0.100000
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* plus the implicit one 1.000000
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MOV rB2, rA2 ; needed later on
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RCALL _U(__fp_split_a) ; does not return on NaN
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ASR rTI0 ; this is dExp!
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PUSH rTI0 ; exponent offset
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X_movw rAbak2, rA2 ; Abak = A
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SUBI rB2, 0x80 ; == EOR 0x80
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CLR rB1 ; a slightly smaller X(0) than the calculated is better
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CLR rB0 ; and saves 2 right shifts
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LDI rB3, 0x3F ; load exponent 7F
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.L_nf: brne .L_pk ; NaN, return as is
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brtc .L_pk ; sqrt(+Inf) --> +Inf
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.L_nan: rjmp _U(__fp_nan)
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.L_pk: rjmp _U(__fp_mpack)
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; split and check arg.
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brcs .L_nf ; !isfinite(A)
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breq .L_pk ; return 0 with original sign
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brts .L_nan ; sqrt(negative) --> NaN
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sbc rB3, rB3 ; exponent high byte
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; normalize, if A is subnormal
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; calculate result exponent
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; expand A mantissa to rAE.rA2.rA1.rA0
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brcc 1f ; after 'ror rA3'
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X_movw rA2, rAbak2 ; A = Abak
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X_movw rBbak2, rB2 ; Bbak = B
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XCALL __divsf3 ; FP1X = arg/xn
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X_movw rB2, rBbak2 ; B = Bbak
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XCALL __addsf3 ; FP1X = arg/xn + xn
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RCALL _U(ldexp) ; div by 2 := Xn+1
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X_movw rB2, rA2 ; B = A
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CPC rBbak3, rB3 ; cmp B to Bbak
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RCALL _U(__fp_split_a) ; does not return on NaN
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; save temporary regs.
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/* arg's mantissa: rAE.rA2.rA1.rA0
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moving bit: mvb2.mvb1.mvb0
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remain value: rem3.rem2.rem1.rem0 */
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cpc rem3, rAE ; C is set if rem < A
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; pop temporary regs.
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; merge result and return
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subi rA3, lo8(-127) ; exponent bias
added
removed
libm/fplib/sqrt.S
