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/* Copyright (c) 2002 Michael Stumpf <mistumpf@de.pepperl-fuchs.com>
Copyright (c) 2006 Dmitry Xmelkov
Copyright (c) 2008 Ruud v Gessel
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: fp_rempio2.S 1810 2008-12-02 13:34:42Z dmix $ */
#include "fp32def.h"
#include "asmdef.h"
/* <non_standart> __fp_rempio2 (float x);
The __fp_rempio2() function computes the remainder of dividing
absolute value of x by Pi/2. The return value is x - n*Pi/2, where
n is the quotient of abs(x)/(Pi/2), rounded towards zero to an integer.
Output:
rA3.rA2.rA1.rA0.rAE - flt40_t remainder
ZL - low byte of n
*/
#define HI40_PIO2 0x3FC90FDA /* (flt40_t) Pi/2 */
#define LO40_PIO2 0xA2
FUNCTION __fp_rempio2
0: rjmp _U(__fp_nan)
ENTRY __fp_rempio2
; split and check finite
rcall _U(__fp_splitA)
brcs 0b ; only finite numbers are valid
clt ; ignore a sign
; init division result
ldi ZL, 0
; extend A
clr rAE
; check (and modify) exponent
subi rA3, hhi8(HI40_PIO2 << 1)
brlo 5f ; fabs(A) < 1.0 radian, C is set
; prepare loop
ldi rB0, lo8(HI40_PIO2)
ldi rB1, hi8(HI40_PIO2)
ldi rB2, hlo8(HI40_PIO2 | 0x800000) ; + hidden bit
rjmp 1f
.Loop: lsl ZL
lsl rAE
rol rA0
rol rA1
rol rA2
brcs 2f
1: cpi rAE, lo8(LO40_PIO2)
cpc rA0, rB0
cpc rA1, rB1
cpc rA2, rB2
brlo 3f
2: subi rAE, lo8(LO40_PIO2)
sbc rA0, rB0
sbc rA1, rB1
sbc rA2, rB2
inc ZL
3: dec rA3
brpl .Loop
; Normalize, we know that rA2.1.0.E >= 0x0E. You can check this with
; a test program below.
cpi rA2,0x80
brcc 5f
4: dec rA3
lsl rAE
rol rA0
rol rA1
rol rA2 ; C := 0
brpl 4b
5: sbci rA3, hhi8((HI40_PIO2<<1) + 0x01000000) ; undo the subi 0x7f
rjmp _U(__fp_mpack_finite)
ENDFUNC
#if 0
/* This is a test program to find the smallest value of rA2.1.0.E after
division. The nonzero value gives a garanty that normalization loop
is finite. */
#include <stdio.h>
#define MNT32_PIO2 0xC90FDAA2
int main ()
{
unsigned long rA210;
unsigned long rA210E;
int rA3;
unsigned long c;
unsigned long amin = 0xffffffff;
for (rA210 = 0x800000; rA210 <= 0xffffff; rA210 += 1) {
rA210E = rA210 << 8;
c = 0;
rA3 = 127; /* this is max for finite number */
goto m;
do {
c = rA210E & 0x80000000;
rA210E <<= 1;
m:
if (c || (rA210E >= MNT32_PIO2))
rA210E -= MNT32_PIO2;
if (rA210E < amin) {
amin = rA210E;
printf ("min of rA210E: 0x%08lx\r", amin);
fflush (stdout);
}
} while (--rA3 >= 0);
}
putchar ('\n');
return 0;
}
#endif
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