base/third_party/dmg_fp/g_fmt.cc

   1 /****************************************************************
   2  *
   3  * The author of this software is David M. Gay.
   4  *
   5  * Copyright (c) 1991, 1996 by Lucent Technologies.
   6  *
   7  * Permission to use, copy, modify, and distribute this software for any
   8  * purpose without fee is hereby granted, provided that this entire notice
   9  * is included in all copies of any software which is or includes a copy
  10  * or modification of this software and in all copies of the supporting
  11  * documentation for such software.
  12  *
  13  * THIS SOFTWARE IS BEING PROVIDED "AS IS", WITHOUT ANY EXPRESS OR IMPLIED
  14  * WARRANTY.  IN PARTICULAR, NEITHER THE AUTHOR NOR LUCENT MAKES ANY
  15  * REPRESENTATION OR WARRANTY OF ANY KIND CONCERNING THE MERCHANTABILITY
  16  * OF THIS SOFTWARE OR ITS FITNESS FOR ANY PARTICULAR PURPOSE.
  17  *
  18  ***************************************************************/
  19
  20 /* g_fmt(buf,x) stores the closest decimal approximation to x in buf;
  21  * it suffices to declare buf
  22  *      char buf[32];
  23  */
  24
  25 #include "dmg_fp.h"
  26
  27 namespace dmg_fp {
  28
  29  char *
  30 g_fmt(register char *b, double x)
  31 {
  32         register int i, k;
  33         register char *s;
  34         int decpt, j, sign;
  35         char *b0, *s0, *se;
  36
  37         b0 = b;
  38 #ifdef IGNORE_ZERO_SIGN
  39         if (!x) {
  40                 *b++ = '0';
  41                 *b = 0;
  42                 goto done;
  43                 }
  44 #endif
  45         s = s0 = dtoa(x, 0, 0, &decpt, &sign, &se);
  46         if (sign)
  47                 *b++ = '-';
  48         if (decpt == 9999) /* Infinity or Nan */ {
  49                 for(*b = *s++; *b++; *b = *s++) {}
  50                 goto done0;
  51                 }
  52         if (decpt <= -4 || decpt > se - s + 5) {
  53                 *b++ = *s++;
  54                 if (*s) {
  55                         *b++ = '.';
  56                         for(*b = *s++; *b; *b = *s++)
  57                                 b++;
  58                         }
  59                 *b++ = 'e';
  60                 /* sprintf(b, "%+.2d", decpt - 1); */
  61                 if (--decpt < 0) {
  62                         *b++ = '-';
  63                         decpt = -decpt;
  64                         }
  65                 else
  66                         *b++ = '+';
  67                 for(j = 2, k = 10; 10*k <= decpt; j++, k *= 10) {}
  68                 for(;;) {
  69                         i = decpt / k;
  70                         *b++ = (char)i + '0';
  71                         if (--j <= 0)
  72                                 break;
  73                         decpt -= i*k;
  74                         decpt *= 10;
  75                         }
  76                 *b = 0;
  77                 }
  78         else if (decpt <= 0) {
  79                 *b++ = '.';
  80                 for(; decpt < 0; decpt++)
  81                         *b++ = '0';
  82                 for(*b = *s++; *b++; *b = *s++) {}
  83                 }
  84         else {
  85                 for(*b = *s++; *b; *b = *s++) {
  86                         b++;
  87                         if (--decpt == 0 && *s)
  88                                 *b++ = '.';
  89                         }
  90                 for(; decpt > 0; decpt--)
  91                         *b++ = '0';
  92                 *b = 0;
  93                 }
  94  done0:
  95         freedtoa(s0);
  96 #ifdef IGNORE_ZERO_SIGN
  97  done:
  98 #endif
  99         return b0;
 100         }
 101
 102 }  // namespace dmg_fp