formats/ctf/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 <babeltrace/ctf/types.h>
  26 #include <glib.h>
  27 #include <float.h>      /* C99 floating point definitions */
  28 #include <limits.h>     /* C99 limits */
  29 #include <endian.h>
  30
  31 /*
  32  * This library is limited to binary representation of floating point values.
  33  * Sign-extension of the exponents is assumed to keep the NaN, +inf, -inf
  34  * values, but this should be double-checked (TODO).
  35  */
  36
  37 /*
  38  * Aliasing float/double and unsigned long is not strictly permitted by strict
  39  * aliasing, but in practice type prunning is well supported, and this permits
  40  * us to use per-word read/writes rather than per-byte.
  41  */
  42
  43 #if defined(__GNUC__) || defined(__MINGW32__) || defined(_MSC_VER)
  44 #define HAS_TYPE_PRUNING
  45 #endif
  46
  47 #if (FLT_RADIX != 2)
  48
  49 #error "Unsupported floating point radix"
  50
  51 #endif
  52
  53 union doubleIEEE754 {
  54         double v;
  55 #ifdef HAS_TYPE_PRUNING
  56         unsigned long bits[(sizeof(double) + sizeof(unsigned long) - 1) / sizeof(unsigned long)];
  57 #else
  58         unsigned char bits[sizeof(double)];
  59 #endif
  60 };
  61
  62 union ldoubleIEEE754 {
  63         long double v;
  64 #ifdef HAS_TYPE_PRUNING
  65         unsigned long bits[(sizeof(long double) + sizeof(unsigned long) - 1) / sizeof(unsigned long)];
  66 #else
  67         unsigned char bits[sizeof(long double)];
  68 #endif
  69 };
  70
  71 struct pos_len {
  72         size_t sign_start, exp_start, mantissa_start, len;
  73 };
  74
  75 void ctf_float_copy(unsigned char *destp, const struct ctf_float *dest,
  76                     const unsigned char *src, const struct ctf_float *src)
  77 {
  78         struct pos_len destpos, srcpos;
  79         union {
  80                 unsigned long long u;
  81                 long long s;
  82         } tmp;
  83
  84         destpos.len = dest.exp_len + dest.mantissa_len;
  85         if (dest.byte_order == LITTLE_ENDIAN) {
  86                 destpos.sign_start = destpos.len - 1;
  87                 destpos.exp_start = destpos.sign_start - dest->exp_len;
  88                 destpos.mantissa_start = 0;
  89         } else {
  90                 destpos.sign_start = 0;
  91                 destpos.exp_start = 1;
  92                 destpos.mantissa_start = destpos.exp_start + dest->exp_len;
  93         }
  94
  95         srcpos.len = src.exp_len + src.mantissa_len;
  96         if (src.byte_order == LITTLE_ENDIAN) {
  97                 srcpos.sign_start = srcpos.len - 1;
  98                 srcpos.exp_start = srcpos.sign_start - src->exp_len;
  99                 srcpos.mantissa_start = 0;
 100         } else {
 101                 srcpos.sign_start = 0;
 102                 srcpos.exp_start = 1;
 103                 srcpos.mantissa_start = srcpos.exp_start + src->exp_len;
 104         }
 105
 106         /* sign */
 107         tmp.u = ctf_bitfield_unsigned_read(ptr, srcpos.sign_start, 1,
 108                                            src->byte_order);
 109         ctf_bitfield_unsigned_write(&u.bits, destpos.sign_start, 1,
 110                                     dest->byte_order, tmp.u);
 111
 112         /* mantissa (without leading 1). No sign extend. */
 113         tmp.u = ctf_bitfield_unsigned_read(ptr, srcpos.mantissa_start,
 114                                            src->mantissa_len - 1,
 115                                            src->byte_order);
 116         ctf_bitfield_unsigned_write(&u.bits, destpos.mantissa_start,
 117                                     dest->mantissa_len - 1, dest->byte_order,
 118                                     tmp.u);
 119
 120         /* exponent, with sign-extend. */
 121         tmp.s = ctf_bitfield_signed_read(ptr, srcpos.exp_start, src->exp_len,
 122                                          src->byte_order);
 123         ctf_bitfield_signed_write(&u.bits, destpos.exp_start, dest->exp_len,
 124                                   dest->byte_order, tmp.s);
 125 }
 126
 127 double ctf_double_read(const unsigned char *ptr, const struct ctf_float *src)
 128 {
 129         union doubleIEEE754 u;
 130         struct ctf_float dest = {
 131                 .exp_len = sizeof(double) * CHAR_BIT - DBL_MANT_DIG,
 132                 .mantissa_len = DBL_MANT_DIG,
 133                 .byte_order = BYTE_ORDER,
 134         };
 135
 136         ctf_float_copy(&u.bits, &dest, ptr, src);
 137         return u.v;
 138 }
 139
 140 size_t ctf_double_write(unsigned char *ptr, const struct ctf_float *dest,
 141                         double v)
 142 {
 143         union doubleIEEE754 u;
 144         struct ctf_float src = {
 145                 .exp_len = sizeof(double) * CHAR_BIT - DBL_MANT_DIG,
 146                 .mantissa_len = DBL_MANT_DIG,
 147                 .byte_order = BYTE_ORDER,
 148         };
 149
 150         if (!ptr)
 151                 goto end;
 152         u.v = v;
 153         ctf_float_copy(ptr, dest, &u.bits, &src);
 154 end:
 155         return len;
 156 }
 157
 158 long double ctf_ldouble_read(const unsigned char *ptr,
 159                              const struct ctf_float *src)
 160 {
 161         union ldoubleIEEE754 u;
 162         struct ctf_float dest = {
 163                 .exp_len = sizeof(double) * CHAR_BIT - LDBL_MANT_DIG,
 164                 .mantissa_len = LDBL_MANT_DIG,
 165                 .byte_order = BYTE_ORDER,
 166         };
 167
 168         ctf_float_copy(&u.bits, &dest, ptr, src);
 169         return u.v;
 170 }
 171
 172 size_t ctf_ldouble_write(unsigned char *ptr, const struct ctf_float *dest,
 173                          long double v)
 174 {
 175         union ldoubleIEEE754 u;
 176         struct ctf_float src = {
 177                 .exp_len = sizeof(double) * CHAR_BIT - LDBL_MANT_DIG,
 178                 .mantissa_len = LDBL_MANT_DIG,
 179                 .byte_order = BYTE_ORDER,
 180         };
 181
 182         if (!ptr)
 183                 goto end;
 184         u.v = v;
 185         ctf_float_copy(ptr, dest, &u.bits, &src);
 186 end:
 187         return len;
 188 }