compilers/bcc/linux86-0.16.17/libc/i386fp/ecvt.c

   1
   2 #define DIGMAX  30              /* max # of digits in string */
   3 #define DIGPREC 17              /* max # of significant digits */
   4 #define ECVT    0
   5 #define FCVT    1
   6 static char digstr[DIGMAX + 1 + 1];    /* +1 for end of string         */
   7
   8     /* +1 in case rounding adds     */
   9     /* another digit                */
  10 static double negtab[] =
  11     { 1e-256, 1e-128, 1e-64, 1e-32, 1e-16, 1e-8, 1e-4, 1e-2, 1e-1, 1.0 };
  12 static double postab[] =
  13     { 1e+256, 1e+128, 1e+64, 1e+32, 1e+16, 1e+8, 1e+4, 1e+2, 1e+1 };
  14
  15 static char *_cvt();
  16
  17 /*************************
  18  * Convert double val to a string of
  19  * decimal digits.
  20  *      ndig = # of digits in resulting string
  21  * Returns:
  22  *      *pdecpt = position of decimal point from left of first digit
  23  *      *psign  = nonzero if value was negative
  24  */
  25 char *
  26 ecvt(val, ndig, pdecpt, psign)
  27 double val;
  28 int   ndig, *pdecpt, *psign;
  29
  30 {
  31    return _cvt(ECVT, val, ndig, pdecpt, psign);
  32 }
  33
  34 char *
  35 fcvt(val, nfrac, pdecpt, psign)
  36 double val;
  37 int   nfrac, *pdecpt, *psign;
  38
  39 {
  40    return _cvt(FCVT, val, nfrac, pdecpt, psign);
  41 }
  42
  43 static char *
  44 _cvt(cnvflag, val, ndig, pdecpt, psign)
  45 double val;
  46 int   ndig, *pdecpt, *psign;
  47
  48 {
  49    int   decpt, pow, i;
  50    char *p;
  51    *psign = (val < 0) ? ((val = -val), 1) : 0;
  52    ndig = (ndig < 0) ? 0 : (ndig < DIGMAX) ? ndig : DIGMAX;
  53    if (val == 0) {
  54       for (p = &digstr[0]; p < &digstr[ndig]; p++)
  55          *p = '0';
  56       decpt = 0;
  57    } else {
  58       /* Adjust things so that 1 <= val < 10  */
  59       /* in these loops if val == MAXDOUBLE)  */
  60       decpt = 1;
  61       pow = 256;
  62       i = 0;
  63       while (val < 1) {
  64          while (val < negtab[i + 1]) {
  65             val /= negtab[i];
  66             decpt -= pow;
  67          }
  68          pow >>= 1;
  69          i++;
  70       }
  71       pow = 256;
  72       i = 0;
  73       while (val >= 10) {
  74          while (val >= postab[i]) {
  75             val /= postab[i];
  76             decpt += pow;
  77          }
  78          pow >>= 1;
  79          i++;
  80       }
  81       if (cnvflag == FCVT) {
  82          ndig += decpt;
  83          ndig = (ndig < 0) ? 0 : (ndig < DIGMAX) ? ndig : DIGMAX;
  84       }
  85
  86       /* Pick off digits 1 by 1 and stuff into digstr[]       */
  87       /* Do 1 extra digit for rounding purposes               */
  88       for (p = &digstr[0]; p <= &digstr[ndig]; p++) {
  89          int   n;
  90
  91          /* 'twould be silly to have zillions of digits  */
  92          /* when only DIGPREC are significant            */
  93          if (p >= &digstr[DIGPREC])
  94             *p = '0';
  95
  96          else {
  97             n = val;
  98             *p = n + '0';
  99             val = (val - n) * 10;       /* get next digit */
 100          }
 101       }
 102       if (*--p >= '5') {        /* if we need to round              */
 103          while (1) {
 104             if (p == &digstr[0]) {      /* if at start      */
 105                ndig += cnvflag;
 106                decpt++;         /* shift dec pnt */
 107                digstr[0] = '1'; /* "100000..." */
 108                break;
 109             }
 110             *p = '0';
 111             --p;
 112             if (*p != '9') {
 113                (*p)++;
 114                break;
 115             }
 116          }                      /* while */
 117       }                         /* if */
 118    }                            /* else */
 119    *pdecpt = decpt;
 120    digstr[ndig] = 0;            /* terminate string             */
 121    return &digstr[0];
 122 }