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129 lines
4.2 KiB
C
129 lines
4.2 KiB
C
/*
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* poly_2xm1.c
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*
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* Function to compute 2^x-1 by a polynomial approximation.
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*
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*
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* Copyright (C) 1992, 1993 W. Metzenthen, 22 Parker St, Ormond,
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* Vic 3163, Australia.
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* E-mail apm233m@vaxc.cc.monash.edu.au
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* All rights reserved.
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*
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* This copyright notice covers the redistribution and use of the
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* FPU emulator developed by W. Metzenthen. It covers only its use
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* in the 386BSD operating system. Any other use is not permitted
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* under this copyright.
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*
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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
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* are met:
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* 1. 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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* 2. Redistributions in binary form must include information specifying
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* that source code for the emulator is freely available and include
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* either:
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* a) an offer to provide the source code for a nominal distribution
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* fee, or
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* b) list at least two alternative methods whereby the source
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* can be obtained, e.g. a publically accessible bulletin board
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* and an anonymous ftp site from which the software can be
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* downloaded.
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* 3. All advertising materials specifically mentioning features or use of
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* this emulator must acknowledge that it was developed by W. Metzenthen.
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* 4. The name of W. Metzenthen may not be used to endorse or promote
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* products derived from this software without specific prior written
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* permission.
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*
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* THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
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* INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
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* AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
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* W. METZENTHEN BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
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* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
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* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
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* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
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* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*
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*/
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#include "exception.h"
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#include "reg_constant.h"
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#include "fpu_emu.h"
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#define HIPOWER 13
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static unsigned short lterms[HIPOWER][4] =
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{
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{0x79b5, 0xd1cf, 0x17f7, 0xb172},
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{0x1b56, 0x058b, 0x7bff, 0x3d7f},
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{0x8bb0, 0x8250, 0x846b, 0x0e35},
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{0xbc65, 0xf747, 0x556d, 0x0276},
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{0x17cb, 0x9e39, 0x61ff, 0x0057},
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{0xe018, 0x9776, 0x1848, 0x000a},
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{0x66f2, 0xff30, 0xffe5, 0x0000},
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{0x682f, 0xffb6, 0x162b, 0x0000},
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{0xb7ca, 0x2956, 0x01b5, 0x0000},
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{0xcd3e, 0x4817, 0x001e, 0x0000},
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{0xb7e2, 0xecbe, 0x0001, 0x0000},
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{0x0ed5, 0x1a27, 0x0000, 0x0000},
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{0x101d, 0x0222, 0x0000, 0x0000},
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};
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/*--- poly_2xm1() -----------------------------------------------------------+
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+---------------------------------------------------------------------------*/
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int
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poly_2xm1(FPU_REG * arg, FPU_REG * result)
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{
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short exponent;
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long long Xll;
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FPU_REG accum;
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exponent = arg->exp - EXP_BIAS;
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if (arg->tag == TW_Zero) {
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/* Return 0.0 */
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reg_move(&CONST_Z, result);
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return 0;
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}
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if (exponent >= 0) { /* Can't hack a number >= 1.0 */
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arith_invalid(result); /* Number too large */
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return 1;
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}
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if (arg->sign != SIGN_POS) { /* Can't hack a number < 0.0 */
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arith_invalid(result); /* Number negative */
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return 1;
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}
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if (exponent < -64) {
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reg_move(&CONST_LN2, result);
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return 0;
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}
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*(unsigned *) &Xll = arg->sigl;
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*(((unsigned *) &Xll) + 1) = arg->sigh;
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if (exponent < -1) {
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/* shift the argument right by the required places */
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if (shrx(&Xll, -1 - exponent) >= (unsigned)0x80000000)
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Xll++; /* round up */
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}
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*(short *) &(accum.sign) = 0; /* will be a valid positive nr with
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* expon = 0 */
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accum.exp = 0;
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/* Do the basic fixed point polynomial evaluation */
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polynomial((unsigned *) &accum.sigl, (unsigned *) &Xll, lterms, HIPOWER - 1);
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/* Convert to 64 bit signed-compatible */
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accum.exp += EXP_BIAS - 1;
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reg_move(&accum, result);
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normalize(result);
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return 0;
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}
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