| 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 "defs.h" |
| 21 | #include "ieee-float.h" |
| 22 | #include <math.h> /* ldexp */ |
| 23 | |
| 24 | /* Convert an IEEE extended float to a double. |
| 25 | FROM is the address of the extended float. |
| 26 | Store the double in *TO. */ |
| 27 | |
| 28 | void |
| 29 | ieee_extended_to_double (ext_format, from, to) |
| 30 | const struct ext_format *ext_format; |
| 31 | char *from; |
| 32 | double *to; |
| 33 | { |
| 34 | unsigned char *ufrom = (unsigned char *)from; |
| 35 | double dto; |
| 36 | unsigned long mant0, mant1, exponent; |
| 37 | |
| 38 | memcpy (&mant0, &from[MANBYTE_H], 4); |
| 39 | memcpy (&mant1, &from[MANBYTE_L], 4); |
| 40 | exponent = ((ufrom[EXPBYTE_H] & (unsigned char)~SIGNMASK) << 8) | ufrom[EXPBYTE_L]; |
| 41 | |
| 42 | #if 0 |
| 43 | /* We can't do anything useful with a NaN anyway, so ignore its |
| 44 | difference. It will end up as Infinity or something close. */ |
| 45 | if (exponent == EXT_EXP_NAN) { |
| 46 | /* We have a NaN source. */ |
| 47 | dto = 0.123456789; /* Not much else useful to do -- we don't know if |
| 48 | the host system even *has* NaNs, nor how to |
| 49 | generate an innocuous one if it does. */ |
| 50 | } else |
| 51 | #endif |
| 52 | if (exponent == 0 && mant0 == 0 && mant1 == 0) { |
| 53 | dto = 0; |
| 54 | } else { |
| 55 | /* Build the result algebraically. Might go infinite, underflow, etc; |
| 56 | who cares. */ |
| 57 | mant0 |= 0x80000000; |
| 58 | dto = ldexp ((double)mant0, exponent - EXT_EXP_BIAS - 31); |
| 59 | dto += ldexp ((double)mant1, exponent - EXT_EXP_BIAS - 31 - 32); |
| 60 | if (ufrom[EXPBYTE_H] & SIGNMASK) /* If negative... */ |
| 61 | dto = -dto; /* ...negate. */ |
| 62 | } |
| 63 | *to = dto; |
| 64 | } |
| 65 | |
| 66 | /* The converse: convert the double *FROM to an extended float |
| 67 | and store where TO points. */ |
| 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 = *from; |
| 76 | unsigned long twolongs[2]; |
| 77 | unsigned long mant0, mant1, exponent; |
| 78 | unsigned char tobytes[8]; |
| 79 | |
| 80 | memset (to, 0, TOTALSIZE); |
| 81 | if (dfrom == 0) |
| 82 | return; /* Result is zero */ |
| 83 | if (dfrom != dfrom) { |
| 84 | /* From is NaN */ |
| 85 | to[EXPBYTE_H] = (unsigned char)(EXT_EXP_NAN >> 8); |
| 86 | to[EXPBYTE_L] = (unsigned char)EXT_EXP_NAN; |
| 87 | to[MANBYTE_H] = 1; /* Be sure it's not infinity, but NaN value is irrel */ |
| 88 | return; /* Result is NaN */ |
| 89 | } |
| 90 | if (dfrom < 0) |
| 91 | to[SIGNBYTE] |= SIGNMASK; /* Set negative sign */ |
| 92 | /* How to tell an infinity from an ordinary number? FIXME-someday */ |
| 93 | |
| 94 | /* The following code assumes that the host has IEEE doubles. FIXME-someday. |
| 95 | It also assumes longs are 32 bits! FIXME-someday. */ |
| 96 | memcpy (twolongs, from, 8); |
| 97 | memcpy (tobytes, from, 8); |
| 98 | #if HOST_BYTE_ORDER == BIG_ENDIAN |
| 99 | exponent = ((tobytes[1] & 0xF0) >> 4) | (tobytes[0] & 0x7F) << 4; |
| 100 | mant0 = (twolongs[0] << 11) | twolongs[1] >> 21; |
| 101 | mant1 = (twolongs[1] << 11); |
| 102 | #else |
| 103 | exponent = ((tobytes[6] & 0xF0) >> 4) | (tobytes[7] & 0x7F) << 4; |
| 104 | mant0 = (twolongs[1] << 11) | twolongs[0] >> 21; |
| 105 | mant1 = (twolongs[0] << 11); |
| 106 | #endif |
| 107 | |
| 108 | /* Fiddle with leading 1-bit, implied in double, explicit in extended. */ |
| 109 | if (exponent == 0) |
| 110 | mant0 &= 0x7FFFFFFF; |
| 111 | else |
| 112 | mant0 |= 0x80000000; |
| 113 | |
| 114 | exponent -= DBL_EXP_BIAS; /* Get integer exp */ |
| 115 | exponent += EXT_EXP_BIAS; /* Offset for extended */ |
| 116 | |
| 117 | /* OK, now store it in extended format. */ |
| 118 | to[EXPBYTE_H] |= (unsigned char)(exponent >> 8); /* Retain sign */ |
| 119 | to[EXPBYTE_L] = (unsigned char) exponent; |
| 120 | |
| 121 | memcpy (&to[MANBYTE_H], &mant0, 4); |
| 122 | memcpy (&to[MANBYTE_L], &mant1, 4); |
| 123 | } |
| 124 | |
| 125 | |
| 126 | #ifdef IEEE_DEBUG |
| 127 | |
| 128 | /* Test some numbers to see that extended/double conversion works for them. */ |
| 129 | |
| 130 | ieee_test (n) |
| 131 | int n; |
| 132 | { |
| 133 | union { double d; int i[2]; } di; |
| 134 | double result; |
| 135 | int i; |
| 136 | char exten[16]; |
| 137 | extern struct ext_format ext_format_68881; |
| 138 | |
| 139 | for (i = 0; i < n; i++) { |
| 140 | di.i[0] = (random() << 16) | (random() & 0xffff); |
| 141 | di.i[1] = (random() << 16) | (random() & 0xffff); |
| 142 | double_to_ieee_extended (&ext_format_68881, &di.d, exten); |
| 143 | ieee_extended_to_double (&ext_format_68881, exten, &result); |
| 144 | if (di.d != result) |
| 145 | printf ("Differ: %x %x %g => %x %x %g\n", di.d, di.d, result, result); |
| 146 | } |
| 147 | } |
| 148 | |
| 149 | #endif |