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         unsigned long long tmp;
  78         struct pos_len destpos, srcpos;
  79
  80         destpos.len = dest.exp_len + dest.mantissa_len;
  81         if (dest.byte_order == LITTLE_ENDIAN) {
  82                 destpos.sign_start = destpos.len - 1;
  83                 destpos.exp_start = destpos.sign_start - dest->exp_len;
  84                 destpos.mantissa_start = 0;
  85         } else {
  86                 destpos.sign_start = 0;
  87                 destpos.exp_start = 1;
  88                 destpos.mantissa_start = destpos.exp_start + dest->exp_len;
  89         }
  90
  91         srcpos.len = src.exp_len + src.mantissa_len;
  92         if (src.byte_order == LITTLE_ENDIAN) {
  93                 srcpos.sign_start = srcpos.len - 1;
  94                 srcpos.exp_start = srcpos.sign_start - src->exp_len;
  95                 srcpos.mantissa_start = 0;
  96         } else {
  97                 srcpos.sign_start = 0;
  98                 srcpos.exp_start = 1;
  99                 srcpos.mantissa_start = srcpos.exp_start + src->exp_len;
 100         }
 101
 102         /* sign */
 103         tmp = bitfield_unsigned_read(ptr, srcpos.sign_start, 1,
 104                                      src->byte_order);
 105         bitfield_unsigned_write(&u.bits, destpos.sign_start, 1,
 106                                 dest->byte_order, tmp);
 107
 108         /* mantissa (except sign). No sign extend. */
 109         tmp = bitfield_unsigned_read(ptr, srcpos.mantissa_start,
 110                                      src->mantissa_len - 1, src->byte_order);
 111         bitfield_unsigned_write(&u.bits, destpos.mantissa_start,
 112                                 dest->mantissa_len - 1, dest->byte_order, tmp);
 113
 114         /* exponent, with sign-extend. */
 115         tmp = bitfield_signed_read(ptr, srcpos.exp_start, src->exp_len,
 116                                    src->byte_order);
 117         bitfield_signed_write(&u.bits, destpos.exp_start, dest->exp_len,
 118                               dest->byte_order, tmp);
 119 }
 120
 121 double ctf_double_read(const unsigned char *ptr, const struct ctf_float *src)
 122 {
 123         union doubleIEEE754 u;
 124         struct ctf_float dest = {
 125                 .exp_len = sizeof(double) * CHAR_BIT - DBL_MANT_DIG,
 126                 .mantissa_len = DBL_MANT_DIG,
 127                 .byte_order = BYTE_ORDER,
 128         };
 129
 130         float_copy(&u.bits, &dest, ptr, src);
 131         return u.v;
 132 }
 133
 134 size_t ctf_double_write(unsigned char *ptr, const struct ctf_float *dest,
 135                         double v)
 136 {
 137         union doubleIEEE754 u;
 138         struct ctf_float src = {
 139                 .exp_len = sizeof(double) * CHAR_BIT - DBL_MANT_DIG,
 140                 .mantissa_len = DBL_MANT_DIG,
 141                 .byte_order = BYTE_ORDER,
 142         };
 143
 144         if (!ptr)
 145                 goto end;
 146         u.v = v;
 147         float_copy(ptr, dest, &u.bits, &src);
 148 end:
 149         return len;
 150 }
 151
 152 long double ctf_ldouble_read(const unsigned char *ptr,
 153                              const struct ctf_float *src)
 154 {
 155         union ldoubleIEEE754 u;
 156         struct ctf_float dest = {
 157                 .exp_len = sizeof(double) * CHAR_BIT - LDBL_MANT_DIG,
 158                 .mantissa_len = LDBL_MANT_DIG,
 159                 .byte_order = BYTE_ORDER,
 160         };
 161
 162         float_copy(&u.bits, &dest, ptr, src);
 163         return u.v;
 164 }
 165
 166 size_t ctf_ldouble_write(unsigned char *ptr, const struct ctf_float *dest,
 167                          long double v)
 168 {
 169         union ldoubleIEEE754 u;
 170         struct ctf_float src = {
 171                 .exp_len = sizeof(double) * CHAR_BIT - LDBL_MANT_DIG,
 172                 .mantissa_len = LDBL_MANT_DIG,
 173                 .byte_order = BYTE_ORDER,
 174         };
 175
 176         if (!ptr)
 177                 goto end;
 178         u.v = v;
 179         float_copy(ptr, dest, &u.bits, &src);
 180 end:
 181         return len;
 182 }