Return to ieee-float.c CVS log

Up to [Apple XNU] / GNUtools / libg++ / libiberty

Annotation of GNUtools/libg++/libiberty/ieee-float.c, revision 1.1

1.1     ! root        1: /* IEEE floating point support routines, for GDB, the GNU Debugger.
        !             2:    Copyright (C) 1991 Free Software Foundation, Inc.
        !             3: 
        !             4: This file is part of GDB.
        !             5: 
        !             6: This program is free software; you can redistribute it and/or modify
        !             7: it under the terms of the GNU General Public License as published by
        !             8: the Free Software Foundation; either version 2 of the License, or
        !             9: (at your option) any later version.
        !            10: 
        !            11: This program is distributed in the hope that it will be useful,
        !            12: but WITHOUT ANY WARRANTY; without even the implied warranty of
        !            13: MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
        !            14: GNU General Public License for more details.
        !            15: 
        !            16: You should have received a copy of the GNU General Public License
        !            17: along with this program; if not, write to the Free Software
        !            18: Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.  */
        !            19: 
        !            20: #include "ieee-float.h"
        !            21: #include <math.h>              /* ldexp */
        !            22: 
        !            23: /* Convert an IEEE extended float to a double.
        !            24:    FROM is the address of the extended float.
        !            25:    Store the double in *TO.  */
        !            26: 
        !            27: void
        !            28: ieee_extended_to_double (ext_format, from, to)
        !            29:      CONST struct ext_format *ext_format;
        !            30:      char *from;
        !            31:      double *to;
        !            32: {
        !            33:   unsigned char *ufrom = (unsigned char *)from;
        !            34:   double dto;
        !            35:   unsigned long mant0, mant1, exponent;
        !            36:   
        !            37:   memcpy (&mant0, &from[MANBYTE_H], 4);
        !            38:   memcpy (&mant1, &from[MANBYTE_L], 4);
        !            39:   exponent = ((ufrom[EXPBYTE_H] & (unsigned char)~SIGNMASK) << 8) | ufrom[EXPBYTE_L];
        !            40: 
        !            41: #if 0
        !            42:   /* We can't do anything useful with a NaN anyway, so ignore its
        !            43:      difference.  It will end up as Infinity or something close.  */
        !            44:   if (exponent == EXT_EXP_NAN) {
        !            45:     /* We have a NaN source.  */
        !            46:     dto = 0.123456789; /* Not much else useful to do -- we don't know if 
        !            47:                           the host system even *has* NaNs, nor how to
        !            48:                           generate an innocuous one if it does.  */
        !            49:   } else
        !            50: #endif
        !            51:          if (exponent == 0 && mant0 == 0 && mant1 == 0) {
        !            52:     dto = 0;
        !            53:   } else {
        !            54:     /* Build the result algebraically.  Might go infinite, underflow, etc;
        !            55:        who cares. */
        !            56:     mant0 |= 0x80000000;
        !            57:     dto = ldexp  ((double)mant0, exponent - EXT_EXP_BIAS - 31);
        !            58:     dto += ldexp ((double)mant1, exponent - EXT_EXP_BIAS - 31 - 32);
        !            59:     if (ufrom[EXPBYTE_H] & SIGNMASK)   /* If negative... */
        !            60:       dto = -dto;                      /* ...negate.  */
        !            61:   }
        !            62:   memcpy (to, &dto, sizeof (dto));
        !            63: }
        !            64: 
        !            65: /* The converse: convert the double *FROM to an extended float
        !            66:    and store where TO points.  Neither FROM nor TO have any alignment
        !            67:    restrictions.  */
        !            68: 
        !            69: void
        !            70: double_to_ieee_extended (ext_format, from, to)
        !            71:      CONST struct ext_format *ext_format;
        !            72:      double *from;
        !            73:      char *to;
        !            74: {
        !            75:   double dfrom;
        !            76:   unsigned long twolongs[2];
        !            77:   unsigned long mant0, mant1, exponent;
        !            78:   unsigned char tobytes[8];
        !            79: 
        !            80:   memcpy (&dfrom, from, sizeof (dfrom));
        !            81:   memset (to, 0, TOTALSIZE);
        !            82:   if (dfrom == 0)
        !            83:     return;                    /* Result is zero */
        !            84:   if (dfrom != dfrom) {
        !            85:     /* From is NaN */
        !            86:     to[EXPBYTE_H] = (unsigned char)(EXT_EXP_NAN >> 8);
        !            87:     to[EXPBYTE_L] = (unsigned char)EXT_EXP_NAN;
        !            88:     to[MANBYTE_H] = 1; /* Be sure it's not infinity, but NaN value is irrel */
        !            89:     return;                    /* Result is NaN */
        !            90:   }
        !            91:   if (dfrom < 0)
        !            92:     to[SIGNBYTE] |= SIGNMASK;  /* Set negative sign */
        !            93:   /* How to tell an infinity from an ordinary number?  FIXME-someday */
        !            94: 
        !            95:   /* The following code assumes that the host has IEEE doubles.  FIXME-someday.
        !            96:      It also assumes longs are 32 bits!  FIXME-someday.  */
        !            97:   memcpy (twolongs, from, 8);
        !            98:   memcpy (tobytes, from, 8);
        !            99: #if HOST_BYTE_ORDER == BIG_ENDIAN
        !           100:   exponent = ((tobytes[1] & 0xF0) >> 4) | (tobytes[0] & 0x7F) << 4;
        !           101:   mant0 = (twolongs[0] << 11) | twolongs[1] >> 21;
        !           102:   mant1 = (twolongs[1] << 11);
        !           103: #else
        !           104:   exponent = ((tobytes[6] & 0xF0) >> 4) | (tobytes[7] & 0x7F) << 4;
        !           105:   mant0 = (twolongs[1] << 11) | twolongs[0] >> 21;
        !           106:   mant1 = (twolongs[0] << 11);
        !           107: #endif
        !           108: 
        !           109:   /* Fiddle with leading 1-bit, implied in double, explicit in extended. */
        !           110:   if (exponent == 0)
        !           111:     mant0 &= 0x7FFFFFFF;
        !           112:   else
        !           113:     mant0 |= 0x80000000;
        !           114: 
        !           115:   exponent -= DBL_EXP_BIAS;                            /* Get integer exp */
        !           116:   exponent += EXT_EXP_BIAS;                            /* Offset for extended */
        !           117: 
        !           118:   /* OK, now store it in extended format. */
        !           119:   to[EXPBYTE_H] |= (unsigned char)(exponent >> 8);     /* Retain sign */
        !           120:   to[EXPBYTE_L] =  (unsigned char) exponent;
        !           121:   
        !           122:   memcpy (&to[MANBYTE_H], &mant0, 4);
        !           123:   memcpy (&to[MANBYTE_L], &mant1, 4);
        !           124: }
        !           125: 
        !           126: 
        !           127: #ifdef IEEE_DEBUG
        !           128: 
        !           129: /* Test some numbers to see that extended/double conversion works for them.  */
        !           130: 
        !           131: ieee_test (n)
        !           132:      int n;
        !           133: {
        !           134:   union { double d; int i[2]; } di;
        !           135:   double result;
        !           136:   int i;
        !           137:   char exten[16];
        !           138:   extern struct ext_format ext_format_68881;
        !           139: 
        !           140:   for (i = 0; i < n; i++) {
        !           141:     di.i[0] = (random() << 16) | (random() & 0xffff);
        !           142:     di.i[1] = (random() << 16) | (random() & 0xffff);
        !           143:     double_to_ieee_extended (&ext_format_68881, &di.d, exten);
        !           144:     ieee_extended_to_double (&ext_format_68881, exten, &result);
        !           145:     if (di.d != result)
        !           146:       printf ("Differ: %x %x %g => %x %x %g\n", di.d, di.d, result, result);
        !           147:   }
        !           148: }
        !           149: 
        !           150: #endif

This archive runs on limited infrastructure. Preserving old code on modern bandwidth. Automated agents are requested to crawl responsibly.