154 lines
4.8 KiB
C
154 lines
4.8 KiB
C
/* IEEE floating point support routines, for GDB, the GNU Debugger.
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Copyright (C) 1991 Free Software Foundation, Inc.
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This file is part of GDB.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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$Id: ieee-float.c,v 1.1 1994/01/28 12:43:04 pk Exp $
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*/
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#include "ieee-float.h"
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#include <math.h> /* ldexp */
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/* Convert an IEEE extended float to a double.
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FROM is the address of the extended float.
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Store the double in *TO. */
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void
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ieee_extended_to_double (ext_format, from, to)
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CONST struct ext_format *ext_format;
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char *from;
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double *to;
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{
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unsigned char *ufrom = (unsigned char *)from;
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double dto;
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unsigned long mant0, mant1, exponent;
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memcpy (&mant0, &from[MANBYTE_H], 4);
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memcpy (&mant1, &from[MANBYTE_L], 4);
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exponent = ((ufrom[EXPBYTE_H] & (unsigned char)~SIGNMASK) << 8) | ufrom[EXPBYTE_L];
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#if 0
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/* We can't do anything useful with a NaN anyway, so ignore its
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difference. It will end up as Infinity or something close. */
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if (exponent == EXT_EXP_NAN) {
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/* We have a NaN source. */
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dto = 0.123456789; /* Not much else useful to do -- we don't know if
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the host system even *has* NaNs, nor how to
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generate an innocuous one if it does. */
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} else
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#endif
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if (exponent == 0 && mant0 == 0 && mant1 == 0) {
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dto = 0;
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} else {
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/* Build the result algebraically. Might go infinite, underflow, etc;
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who cares. */
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mant0 |= 0x80000000;
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dto = ldexp ((double)mant0, exponent - EXT_EXP_BIAS - 31);
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dto += ldexp ((double)mant1, exponent - EXT_EXP_BIAS - 31 - 32);
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if (ufrom[EXPBYTE_H] & SIGNMASK) /* If negative... */
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dto = -dto; /* ...negate. */
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}
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memcpy (to, &dto, sizeof (dto));
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}
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/* The converse: convert the double *FROM to an extended float
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and store where TO points. Neither FROM nor TO have any alignment
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restrictions. */
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void
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double_to_ieee_extended (ext_format, from, to)
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CONST struct ext_format *ext_format;
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double *from;
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char *to;
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{
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double dfrom;
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unsigned long twolongs[2];
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unsigned long mant0, mant1, exponent;
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unsigned char tobytes[8];
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memcpy (&dfrom, from, sizeof (dfrom));
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memset (to, 0, TOTALSIZE);
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if (dfrom == 0)
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return; /* Result is zero */
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if (dfrom != dfrom) {
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/* From is NaN */
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to[EXPBYTE_H] = (unsigned char)(EXT_EXP_NAN >> 8);
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to[EXPBYTE_L] = (unsigned char)EXT_EXP_NAN;
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to[MANBYTE_H] = 1; /* Be sure it's not infinity, but NaN value is irrel */
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return; /* Result is NaN */
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}
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if (dfrom < 0)
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to[SIGNBYTE] |= SIGNMASK; /* Set negative sign */
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/* How to tell an infinity from an ordinary number? FIXME-someday */
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/* The following code assumes that the host has IEEE doubles. FIXME-someday.
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It also assumes longs are 32 bits! FIXME-someday. */
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memcpy (twolongs, from, 8);
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memcpy (tobytes, from, 8);
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#if HOST_BYTE_ORDER == BIG_ENDIAN
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exponent = ((tobytes[1] & 0xF0) >> 4) | (tobytes[0] & 0x7F) << 4;
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mant0 = (twolongs[0] << 11) | twolongs[1] >> 21;
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mant1 = (twolongs[1] << 11);
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#else
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exponent = ((tobytes[6] & 0xF0) >> 4) | (tobytes[7] & 0x7F) << 4;
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mant0 = (twolongs[1] << 11) | twolongs[0] >> 21;
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mant1 = (twolongs[0] << 11);
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#endif
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/* Fiddle with leading 1-bit, implied in double, explicit in extended. */
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if (exponent == 0)
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mant0 &= 0x7FFFFFFF;
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else
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mant0 |= 0x80000000;
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exponent -= DBL_EXP_BIAS; /* Get integer exp */
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exponent += EXT_EXP_BIAS; /* Offset for extended */
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/* OK, now store it in extended format. */
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to[EXPBYTE_H] |= (unsigned char)(exponent >> 8); /* Retain sign */
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to[EXPBYTE_L] = (unsigned char) exponent;
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memcpy (&to[MANBYTE_H], &mant0, 4);
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memcpy (&to[MANBYTE_L], &mant1, 4);
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}
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#ifdef IEEE_DEBUG
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/* Test some numbers to see that extended/double conversion works for them. */
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ieee_test (n)
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int n;
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{
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union { double d; int i[2]; } di;
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double result;
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int i;
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char exten[16];
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extern struct ext_format ext_format_68881;
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for (i = 0; i < n; i++) {
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di.i[0] = (random() << 16) | (random() & 0xffff);
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di.i[1] = (random() << 16) | (random() & 0xffff);
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double_to_ieee_extended (&ext_format_68881, &di.d, exten);
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ieee_extended_to_double (&ext_format_68881, exten, &result);
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if (di.d != result)
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printf ("Differ: %x %x %g => %x %x %g\n", di.d, di.d, result, result);
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}
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}
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#endif
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