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/*
* poly_2xm1.c
*
* Function to compute 2^x-1 by a polynomial approximation.
*
*
* Copyright (C) 1992, 1993 W. Metzenthen, 22 Parker St, Ormond,
* Vic 3163, Australia.
* E-mail apm233m@vaxc.cc.monash.edu.au
* All rights reserved.
*
* This copyright notice covers the redistribution and use of the
* FPU emulator developed by W. Metzenthen. It covers only its use
* in the 386BSD operating system. Any other use is not permitted
* under this copyright.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must include information specifying
* that source code for the emulator is freely available and include
* either:
* a) an offer to provide the source code for a nominal distribution
* fee, or
* b) list at least two alternative methods whereby the source
* can be obtained, e.g. a publically accessible bulletin board
* and an anonymous ftp site from which the software can be
* downloaded.
* 3. All advertising materials specifically mentioning features or use of
* this emulator must acknowledge that it was developed by W. Metzenthen.
* 4. The name of W. Metzenthen may not be used to endorse or promote
* products derived from this software without specific prior written
* permission.
*
* THIS SOFTWARE IS PROVIDED ``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
* W. METZENTHEN 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.
*
*/
#include "exception.h"
#include "reg_constant.h"
#include "fpu_emu.h"
#define HIPOWER 13
static unsigned short lterms[HIPOWER][4] =
{
{0x79b5, 0xd1cf, 0x17f7, 0xb172},
{0x1b56, 0x058b, 0x7bff, 0x3d7f},
{0x8bb0, 0x8250, 0x846b, 0x0e35},
{0xbc65, 0xf747, 0x556d, 0x0276},
{0x17cb, 0x9e39, 0x61ff, 0x0057},
{0xe018, 0x9776, 0x1848, 0x000a},
{0x66f2, 0xff30, 0xffe5, 0x0000},
{0x682f, 0xffb6, 0x162b, 0x0000},
{0xb7ca, 0x2956, 0x01b5, 0x0000},
{0xcd3e, 0x4817, 0x001e, 0x0000},
{0xb7e2, 0xecbe, 0x0001, 0x0000},
{0x0ed5, 0x1a27, 0x0000, 0x0000},
{0x101d, 0x0222, 0x0000, 0x0000},
};
/*--- poly_2xm1() -----------------------------------------------------------+
| |
+---------------------------------------------------------------------------*/
int
poly_2xm1(FPU_REG * arg, FPU_REG * result)
{
short exponent;
long long Xll;
FPU_REG accum;
exponent = arg->exp - EXP_BIAS;
if (arg->tag == TW_Zero) {
/* Return 0.0 */
reg_move(&CONST_Z, result);
return 0;
}
if (exponent >= 0) { /* Can't hack a number >= 1.0 */
arith_invalid(result); /* Number too large */
return 1;
}
if (arg->sign != SIGN_POS) { /* Can't hack a number < 0.0 */
arith_invalid(result); /* Number negative */
return 1;
}
if (exponent < -64) {
reg_move(&CONST_LN2, result);
return 0;
}
*(unsigned *) &Xll = arg->sigl;
*(((unsigned *) &Xll) + 1) = arg->sigh;
if (exponent < -1) {
/* shift the argument right by the required places */
if (shrx(&Xll, -1 - exponent) >= (unsigned)0x80000000)
Xll++; /* round up */
}
*(short *) &(accum.sign) = 0; /* will be a valid positive nr with
* expon = 0 */
accum.exp = 0;
/* Do the basic fixed point polynomial evaluation */
polynomial((unsigned *) &accum.sigl, (unsigned *) &Xll, lterms, HIPOWER - 1);
/* Convert to 64 bit signed-compatible */
accum.exp += EXP_BIAS - 1;
reg_move(&accum, result);
normalize(result);
return 0;
}
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