lib/types/float.c

   1 /*
   2  * Common Trace Format
   3  *
   4  * Floating point read/write functions.
   5  *
   6  * Copyright (c) 2010 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   7  *
   8  * This library is free software; you can redistribute it and/or
   9  * modify it under the terms of the GNU Lesser General Public
  10  * License as published by the Free Software Foundation; either
  11  * version 2.1 of the License, or (at your option) any later version.
  12  *
  13  * This library is distributed in the hope that it will be useful,
  14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  16  * Lesser General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU Lesser General Public
  19  * License along with this library; if not, write to the Free Software
  20  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  21  *
  22  * Reference: ISO C99 standard 5.2.4
  23  */
  24
  25 #include <ctf/ctf-types.h>
  26 #include <glib.h>
  27 #include <float.h>      /* C99 floating point definitions */
  28 #include <endian.h>
  29
  30 /*
  31  * This library is limited to binary representation of floating point values.
  32  * Sign-extension of the exponents is assumed to keep the NaN, +inf, -inf
  33  * values, but this should be double-checked (TODO).
  34  */
  35
  36 /*
  37  * Aliasing float/double and unsigned long is not strictly permitted by strict
  38  * aliasing, but in practice type prunning is well supported, and this permits
  39  * us to use per-word read/writes rather than per-byte.
  40  */
  41
  42 #if defined(__GNUC__) || defined(__MINGW32__) || defined(_MSC_VER)
  43 #define HAS_TYPE_PRUNING
  44 #endif
  45
  46 #if (FLT_RADIX != 2)
  47
  48 #error "Unsupported floating point radix"
  49
  50 #endif
  51
  52 union doubleIEEE754 {
  53         double v;
  54 #ifdef HAS_TYPE_PRUNING
  55         unsigned long bits[(sizeof(double) + sizeof(unsigned long) - 1) / sizeof(unsigned long)];
  56 #else
  57         unsigned char bits[sizeof(double)];
  58 #endif
  59 };
  60
  61 union ldoubleIEEE754 {
  62         long double v;
  63 #ifdef HAS_TYPE_PRUNING
  64         unsigned long bits[(sizeof(long double) + sizeof(unsigned long) - 1) / sizeof(unsigned long)];
  65 #else
  66         unsigned char bits[sizeof(long double)];
  67 #endif
  68 };
  69
  70 struct pos_len {
  71         size_t sign_start, exp_start, mantissa_start, len;
  72 };
  73
  74 void ctf_float_copy(unsigned char *destp, const struct ctf_float *dest,
  75                     const unsigned char *src, const struct ctf_float *src)
  76 {
  77         struct pos_len destpos, srcpos;
  78         union {
  79                 unsigned long long u;
  80                 long long s;
  81         } tmp;
  82
  83         destpos.len = dest.exp_len + dest.mantissa_len;
  84         if (dest.byte_order == LITTLE_ENDIAN) {
  85                 destpos.sign_start = destpos.len - 1;
  86                 destpos.exp_start = destpos.sign_start - dest->exp_len;
  87                 destpos.mantissa_start = 0;
  88         } else {
  89                 destpos.sign_start = 0;
  90                 destpos.exp_start = 1;
  91                 destpos.mantissa_start = destpos.exp_start + dest->exp_len;
  92         }
  93
  94         srcpos.len = src.exp_len + src.mantissa_len;
  95         if (src.byte_order == LITTLE_ENDIAN) {
  96                 srcpos.sign_start = srcpos.len - 1;
  97                 srcpos.exp_start = srcpos.sign_start - src->exp_len;
  98                 srcpos.mantissa_start = 0;
  99         } else {
 100                 srcpos.sign_start = 0;
 101                 srcpos.exp_start = 1;
 102                 srcpos.mantissa_start = srcpos.exp_start + src->exp_len;
 103         }
 104
 105         /* sign */
 106         tmp.u = bitfield_unsigned_read(ptr, srcpos.sign_start, 1,
 107                                        src->byte_order);
 108         bitfield_unsigned_write(&u.bits, destpos.sign_start, 1,
 109                                 dest->byte_order, tmp.u);
 110
 111         /* mantissa (without leading 1). No sign extend. */
 112         tmp.u = bitfield_unsigned_read(ptr, srcpos.mantissa_start,
 113                                        src->mantissa_len - 1, src->byte_order);
 114         bitfield_unsigned_write(&u.bits, destpos.mantissa_start,
 115                                 dest->mantissa_len - 1, dest->byte_order, tmp.u);
 116
 117         /* exponent, with sign-extend. */
 118         tmp.s = bitfield_signed_read(ptr, srcpos.exp_start, src->exp_len,
 119                                      src->byte_order);
 120         bitfield_signed_write(&u.bits, destpos.exp_start, dest->exp_len,
 121                               dest->byte_order, tmp.s);
 122 }
 123
 124 double ctf_double_read(const unsigned char *ptr, const struct ctf_float *src)
 125 {
 126         union doubleIEEE754 u;
 127         struct ctf_float dest = {
 128                 .exp_len = sizeof(double) * CHAR_BIT - DBL_MANT_DIG,
 129                 .mantissa_len = DBL_MANT_DIG,
 130                 .byte_order = BYTE_ORDER,
 131         };
 132
 133         float_copy(&u.bits, &dest, ptr, src);
 134         return u.v;
 135 }
 136
 137 size_t ctf_double_write(unsigned char *ptr, const struct ctf_float *dest,
 138                         double v)
 139 {
 140         union doubleIEEE754 u;
 141         struct ctf_float src = {
 142                 .exp_len = sizeof(double) * CHAR_BIT - DBL_MANT_DIG,
 143                 .mantissa_len = DBL_MANT_DIG,
 144                 .byte_order = BYTE_ORDER,
 145         };
 146
 147         if (!ptr)
 148                 goto end;
 149         u.v = v;
 150         float_copy(ptr, dest, &u.bits, &src);
 151 end:
 152         return len;
 153 }
 154
 155 long double ctf_ldouble_read(const unsigned char *ptr,
 156                              const struct ctf_float *src)
 157 {
 158         union ldoubleIEEE754 u;
 159         struct ctf_float dest = {
 160                 .exp_len = sizeof(double) * CHAR_BIT - LDBL_MANT_DIG,
 161                 .mantissa_len = LDBL_MANT_DIG,
 162                 .byte_order = BYTE_ORDER,
 163         };
 164
 165         float_copy(&u.bits, &dest, ptr, src);
 166         return u.v;
 167 }
 168
 169 size_t ctf_ldouble_write(unsigned char *ptr, const struct ctf_float *dest,
 170                          long double v)
 171 {
 172         union ldoubleIEEE754 u;
 173         struct ctf_float src = {
 174                 .exp_len = sizeof(double) * CHAR_BIT - LDBL_MANT_DIG,
 175                 .mantissa_len = LDBL_MANT_DIG,
 176                 .byte_order = BYTE_ORDER,
 177         };
 178
 179         if (!ptr)
 180                 goto end;
 181         u.v = v;
 182         float_copy(ptr, dest, &u.bits, &src);
 183 end:
 184         return len;
 185 }