UNIX 7th Ed. - /usr/src/libc/gen/atof.c

   1: /*
   2: 	C library - ascii to floating
   3: */
   4: 
   5: #include <math.h>
   6: #include <ctype.h>
   7: 
   8: double
   9: atof(p)
  10: register char *p;
  11: {
  12:     register c;
  13:     double fl, flexp, exp5;
  14:     double big = 72057594037927936.;  /*2^56*/
  15:     double ldexp();
  16:     int nd;
  17:     register eexp, exp, neg, negexp, bexp;
  18: 
  19:     neg = 1;
  20:     while((c = *p++) == ' ')
  21:         ;
  22:     if (c == '-')
  23:         neg = -1;
  24:     else if (c=='+')
  25:         ;
  26:     else
  27:         --p;
  28: 
  29:     exp = 0;
  30:     fl = 0;
  31:     nd = 0;
  32:     while ((c = *p++), isdigit(c)) {
  33:         if (fl<big)
  34:             fl = 10*fl + (c-'0');
  35:         else
  36:             exp++;
  37:         nd++;
  38:     }
  39: 
  40:     if (c == '.') {
  41:         while ((c = *p++), isdigit(c)) {
  42:             if (fl<big) {
  43:                 fl = 10*fl + (c-'0');
  44:                 exp--;
  45:             }
  46:         nd++;
  47:         }
  48:     }
  49: 
  50:     negexp = 1;
  51:     eexp = 0;
  52:     if ((c == 'E') || (c == 'e')) {
  53:         if ((c= *p++) == '+')
  54:             ;
  55:         else if (c=='-')
  56:             negexp = -1;
  57:         else
  58:             --p;
  59: 
  60:         while ((c = *p++), isdigit(c)) {
  61:             eexp = 10*eexp+(c-'0');
  62:         }
  63:         if (negexp<0)
  64:             eexp = -eexp;
  65:         exp = exp + eexp;
  66:     }
  67: 
  68:     negexp = 1;
  69:     if (exp<0) {
  70:         negexp = -1;
  71:         exp = -exp;
  72:     }
  73: 
  74: 
  75:     if((nd+exp*negexp) < -LOGHUGE){
  76:         fl = 0;
  77:         exp = 0;
  78:     }
  79:     flexp = 1;
  80:     exp5 = 5;
  81:     bexp = exp;
  82:     for (;;) {
  83:         if (exp&01)
  84:             flexp *= exp5;
  85:         exp >>= 1;
  86:         if (exp==0)
  87:             break;
  88:         exp5 *= exp5;
  89:     }
  90:     if (negexp<0)
  91:         fl /= flexp;
  92:     else
  93:         fl *= flexp;
  94:     fl = ldexp(fl, negexp*bexp);
  95:     if (neg<0)
  96:         fl = -fl;
  97:     return(fl);
  98: }

Defined functions