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/* Copyright (c) 2007 Dmitry Xmelkov
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. */
/* $Id: round.S,v 1.1 2007/11/05 11:12:51 dmix Exp $ */
#include "fp32def.h"
#include "asmdef.h"
/* double round (double A);
The round() function rounds A to the nearest integer, but rounds
halfway cases away from zero (instead of to the nearest even
integer). Overflow is impossible.
Return:
The rounded value. If A is an integral or infinite, A itself is
returned. If A is NaN, then NaN is returned.
Algorithm roughly:
- split
- shift right to obtain the 0.5 at the little bit
- if the little bit is set, add 1 to mantissa
- merge to float
This is a balance between space and speed.
*/
ENTRY round
rcall _U(__fp_splitA)
brcs .L_nf
; A is finite
cpi rA3, 126 ; exponent field of 0.5
brlo .L_zr ; A is too small
; fabs(A) >= 0x0.800000p+00
cpi rA3, 126+24
brsh 4f ; A is too big
; fabs(A) <= 0x0.ffffffp+23
1: cpi rA3, 126+16
brsh 3f ; shift by 0..7 positions is needed
; quick shift by 8
mov rA0, rA1
mov rA1, rA2
clr rA2
subi rA3, -8
rjmp 1b
; slow shift
2: lsr rA2
ror rA1
ror rA0
inc rA3
3: cpi rA3, 126+23
brlo 2b
; round
mov rAE, rA0
andi rAE, 1
add rA0, rAE
adc rA1, r1
adc rA2, r1
; check and correct a possible overflow
brcc 4f
ror rA2
ror rA1
ror rA0
inc rA3
; merge
4: rjmp _U(__fp_mintl)
.L_nf: rjmp _U(__fp_mpack) ; pass nonfinite arg "as is"
.L_zr: rjmp _U(__fp_szero) ; return +0.0/-0.0
ENDFUNC
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