external/io_grib1/WGRIB/flt2ieee.c

   1 #include <stdio.h>
   2 #include <stdlib.h>
   3 #include <math.h>
   4 #include <float.h>
   5 #include "grib.h"
   6
   7 /*
   8  * convert a float to an ieee single precision number v1.1
   9  * (big endian)
  10  *                      Wesley Ebisuzaki
  11  *
  12  * bugs: doesn't handle subnormal numbers
  13  * bugs: assumes length of integer >= 25 bits
  14  */
  15
  16 int flt2ieee(float x, unsigned char *ieee) {
  17
  18         int sign, exp;
  19         unsigned int umant;
  20         double mant;
  21
  22         if (x == 0.0) {
  23                 ieee[0] = ieee[1] = ieee[2] = ieee[3] = 0;
  24                 return 0;
  25         }
  26
  27         /* sign bit */
  28         if (x < 0.0) {
  29                 sign = 128;
  30                 x = -x;
  31         }
  32         else sign = 0;
  33         mant = frexp((double) x, &exp);
  34
  35         /* 2^24 = 16777216 */
  36
  37         umant = mant * 16777216 + 0.5;
  38         if (umant >= 16777216) {
  39             umant = umant / 2;
  40             exp++;
  41         }
  42         /* bit 24 should be a 1 .. not used in ieee format */
  43
  44         exp = exp - 1 + 127;
  45
  46         if (exp < 0) {
  47                 /* signed zero */
  48                 ieee[0] = sign;
  49                 ieee[1] = ieee[2] = ieee[3] = 0;
  50                 return 0;
  51         }
  52         if (exp > 255) {
  53                 /* signed infinity */
  54                 ieee[0] = sign + 127;
  55                 ieee[1] = 128;
  56                 ieee[2] = ieee[3] = 0;
  57                 return 0;
  58         }
  59         /* normal number */
  60
  61         ieee[0] = sign + (exp >> 1);
  62
  63         ieee[3] = umant & 255;
  64         ieee[2] = (umant >> 8) & 255;
  65         ieee[1] = ((exp & 1) << 7) + ((umant >> 16) & 127);
  66         return 0;
  67 }