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/* IEEE floating point support routines, for GDB, the GNU Debugger. Copyright (C) 1991 Free Software Foundation, Inc. This file is part of GDB. This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. */ #include "defs.h" #include "ieee-float.h" #include <math.h> /* ldexp */ /* Convert an IEEE extended float to a double. FROM is the address of the extended float. Store the double in *TO. */ void ieee_extended_to_double (ext_format, from, to) const struct ext_format *ext_format; char *from; double *to; { unsigned char *ufrom = (unsigned char *)from; double dto; unsigned long mant0, mant1, exponent; memcpy (&mant0, &from[MANBYTE_H], 4); memcpy (&mant1, &from[MANBYTE_L], 4); exponent = ((ufrom[EXPBYTE_H] & (unsigned char)~SIGNMASK) << 8) | ufrom[EXPBYTE_L]; #if 0 /* We can't do anything useful with a NaN anyway, so ignore its difference. It will end up as Infinity or something close. */ if (exponent == EXT_EXP_NAN) { /* We have a NaN source. */ dto = 0.123456789; /* Not much else useful to do -- we don't know if the host system even *has* NaNs, nor how to generate an innocuous one if it does. */ } else #endif if (exponent == 0 && mant0 == 0 && mant1 == 0) { dto = 0; } else { /* Build the result algebraically. Might go infinite, underflow, etc; who cares. */ mant0 |= 0x80000000; dto = ldexp ((double)mant0, exponent - EXT_EXP_BIAS - 31); dto += ldexp ((double)mant1, exponent - EXT_EXP_BIAS - 31 - 32); if (ufrom[EXPBYTE_H] & SIGNMASK) /* If negative... */ dto = -dto; /* ...negate. */ } *to = dto; } /* The converse: convert the double *FROM to an extended float and store where TO points. */ void double_to_ieee_extended (ext_format, from, to) const struct ext_format *ext_format; double *from; char *to; { double dfrom = *from; unsigned long twolongs[2]; unsigned long mant0, mant1, exponent; unsigned char tobytes[8]; memset (to, 0, TOTALSIZE); if (dfrom == 0) return; /* Result is zero */ if (dfrom != dfrom) { /* From is NaN */ to[EXPBYTE_H] = (unsigned char)(EXT_EXP_NAN >> 8); to[EXPBYTE_L] = (unsigned char)EXT_EXP_NAN; to[MANBYTE_H] = 1; /* Be sure it's not infinity, but NaN value is irrel */ return; /* Result is NaN */ } if (dfrom < 0) to[SIGNBYTE] |= SIGNMASK; /* Set negative sign */ /* How to tell an infinity from an ordinary number? FIXME-someday */ /* The following code assumes that the host has IEEE doubles. FIXME-someday. It also assumes longs are 32 bits! FIXME-someday. */ memcpy (twolongs, from, 8); memcpy (tobytes, from, 8); #if HOST_BYTE_ORDER == BIG_ENDIAN exponent = ((tobytes[1] & 0xF0) >> 4) | (tobytes[0] & 0x7F) << 4; mant0 = (twolongs[0] << 11) | twolongs[1] >> 21; mant1 = (twolongs[1] << 11); #else exponent = ((tobytes[6] & 0xF0) >> 4) | (tobytes[7] & 0x7F) << 4; mant0 = (twolongs[1] << 11) | twolongs[0] >> 21; mant1 = (twolongs[0] << 11); #endif /* Fiddle with leading 1-bit, implied in double, explicit in extended. */ if (exponent == 0) mant0 &= 0x7FFFFFFF; else mant0 |= 0x80000000; exponent -= DBL_EXP_BIAS; /* Get integer exp */ exponent += EXT_EXP_BIAS; /* Offset for extended */ /* OK, now store it in extended format. */ to[EXPBYTE_H] |= (unsigned char)(exponent >> 8); /* Retain sign */ to[EXPBYTE_L] = (unsigned char) exponent; memcpy (&to[MANBYTE_H], &mant0, 4); memcpy (&to[MANBYTE_L], &mant1, 4); } #ifdef IEEE_DEBUG /* Test some numbers to see that extended/double conversion works for them. */ ieee_test (n) int n; { union { double d; int i[2]; } di; double result; int i; char exten[16]; extern struct ext_format ext_format_68881; for (i = 0; i < n; i++) { di.i[0] = (random() << 16) | (random() & 0xffff); di.i[1] = (random() << 16) | (random() & 0xffff); double_to_ieee_extended (&ext_format_68881, &di.d, exten); ieee_extended_to_double (&ext_format_68881, exten, &result); if (di.d != result) printf ("Differ: %x %x %g => %x %x %g\n", di.d, di.d, result, result); } } #endif

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