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 /* TODO */
  76
  77 void ctf_float_copy(unsigned char *destp, const struct type_class_float *dest,
  78                     const unsigned char *src, const struct type_class_float *src)
  79 {
  80         struct pos_len destpos, srcpos;
  81         union {
  82                 unsigned long long u;
  83                 long long s;
  84         } tmp;
  85
  86         destpos.len = dest->exp_len + dest->mantissa_len;
  87         if (dest->byte_order == LITTLE_ENDIAN) {
  88                 destpos.sign_start = destpos.len - 1;
  89                 destpos.exp_start = destpos.sign_start - dest->exp_len;
  90                 destpos.mantissa_start = 0;
  91         } else {
  92                 destpos.sign_start = 0;
  93                 destpos.exp_start = 1;
  94                 destpos.mantissa_start = destpos.exp_start + dest->exp_len;
  95         }
  96
  97         srcpos.len = src->exp_len + src->mantissa_len;
  98         if (src->byte_order == LITTLE_ENDIAN) {
  99                 srcpos.sign_start = srcpos.len - 1;
 100                 srcpos.exp_start = srcpos.sign_start - src->exp_len;
 101                 srcpos.mantissa_start = 0;
 102         } else {
 103                 srcpos.sign_start = 0;
 104                 srcpos.exp_start = 1;
 105                 srcpos.mantissa_start = srcpos.exp_start + src->exp_len;
 106         }
 107
 108         /* sign */
 109         tmp.u = ctf_bitfield_unsigned_read(ptr, srcpos.sign_start, 1,
 110                                            src->byte_order);
 111         ctf_bitfield_unsigned_write(&u.bits, destpos.sign_start, 1,
 112                                     dest->byte_order, tmp.u);
 113
 114         /* mantissa (without leading 1). No sign extend. */
 115         tmp.u = ctf_bitfield_unsigned_read(ptr, srcpos.mantissa_start,
 116                                            src->mantissa_len - 1,
 117                                            src->byte_order);
 118         ctf_bitfield_unsigned_write(&u.bits, destpos.mantissa_start,
 119                                     dest->mantissa_len - 1, dest->byte_order,
 120                                     tmp.u);
 121
 122         /* exponent, with sign-extend. */
 123         tmp.s = ctf_bitfield_signed_read(ptr, srcpos.exp_start, src->exp_len,
 124                                          src->byte_order);
 125         ctf_bitfield_signed_write(&u.bits, destpos.exp_start, dest->exp_len,
 126                                   dest->byte_order, tmp.s);
 127 }
 128
 129 double ctf_double_read(const unsigned char *ptr, const struct type_class_float *src)
 130 {
 131         union doubleIEEE754 u;
 132         struct ctf_float dest = {
 133                 .exp_len = sizeof(double) * CHAR_BIT - DBL_MANT_DIG,
 134                 .mantissa_len = DBL_MANT_DIG,
 135                 .byte_order = BYTE_ORDER,
 136         };
 137
 138         ctf_float_copy(&u.bits, &dest, ptr, src);
 139         return u.v;
 140 }
 141
 142 size_t ctf_double_write(unsigned char *ptr, const struct type_class_float *dest,
 143                         double v)
 144 {
 145         union doubleIEEE754 u;
 146         struct ctf_float src = {
 147                 .exp_len = sizeof(double) * CHAR_BIT - DBL_MANT_DIG,
 148                 .mantissa_len = DBL_MANT_DIG,
 149                 .byte_order = BYTE_ORDER,
 150         };
 151
 152         if (!ptr)
 153                 goto end;
 154         u.v = v;
 155         ctf_float_copy(ptr, dest, &u.bits, &src);
 156 end:
 157         return len;
 158 }
 159
 160 long double ctf_ldouble_read(const unsigned char *ptr,
 161                              const struct type_class_float *src)
 162 {
 163         union ldoubleIEEE754 u;
 164         struct ctf_float dest = {
 165                 .exp_len = sizeof(double) * CHAR_BIT - LDBL_MANT_DIG,
 166                 .mantissa_len = LDBL_MANT_DIG,
 167                 .byte_order = BYTE_ORDER,
 168         };
 169
 170         ctf_float_copy(&u.bits, &dest, ptr, src);
 171         return u.v;
 172 }
 173
 174 size_t ctf_ldouble_write(unsigned char *ptr, const struct type_class_float *dest,
 175                          long double v)
 176 {
 177         union ldoubleIEEE754 u;
 178         struct ctf_float src = {
 179                 .exp_len = sizeof(double) * CHAR_BIT - LDBL_MANT_DIG,
 180                 .mantissa_len = LDBL_MANT_DIG,
 181                 .byte_order = BYTE_ORDER,
 182         };
 183
 184         if (!ptr)
 185                 goto end;
 186         u.v = v;
 187         ctf_float_copy(ptr, dest, &u.bits, &src);
 188 end:
 189         return len;
 190 }