mstr.cpp

   1 // Convert bignum to string
   2
   3 #include "stdafx.h"
   4 #include "defs.h"
   5
   6 static int divby1billion(unsigned int *);
   7
   8 static char *str;
   9 static int len;
  10
  11 char *
  12 mstr(unsigned int *a)
  13 {
  14         int k, n, r, sign;
  15         char c;
  16
  17         if (str == NULL) {
  18                 str = (char *) malloc(1000);
  19                 len = 1000;
  20         }
  21
  22         // estimate string size
  23
  24         n = 10 * MLENGTH(a) + 2;
  25
  26         if (n > len) {
  27                 free(str);
  28                 str = (char *) malloc(n);
  29                 len = n;
  30         }
  31
  32         sign = MSIGN(a);
  33
  34         a = mcopy(a);
  35
  36         k = len - 1;
  37
  38         str[k] = 0;
  39
  40         for (;;) {
  41                 k -= 9;
  42                 r = divby1billion(a);
  43                 c = str[k + 9];
  44                 sprintf(str + k, "%09d", r);
  45                 str[k + 9] = c;
  46                 if (MZERO(a))
  47                         break;
  48         }
  49
  50         // remove leading zeroes
  51
  52         while (str[k] == '0')
  53                 k++;
  54
  55         if (str[k] == 0)
  56                 k--;
  57
  58         // sign
  59
  60         if (sign == -1) {
  61                 k--;
  62                 str[k] = '-';
  63         }
  64
  65         mfree(a);
  66
  67         return str + k;
  68 }
  69
  70 // Returns remainder as function value, quotient returned in a.
  71
  72 static int
  73 divby1billion(unsigned int *a)
  74 {
  75         int i;
  76         unsigned long long kk;
  77
  78         kk = 0;
  79
  80         for (i = MLENGTH(a) - 1; i >= 0; i--) {
  81
  82                 if (little_endian()) {
  83                         ((unsigned int *) &kk)[1] = ((unsigned int *) &kk)[0];
  84                         ((unsigned int *) &kk)[0] = a[i];
  85                 } else {
  86                         ((unsigned int *) &kk)[0] = ((unsigned int *) &kk)[1];
  87                         ((unsigned int *) &kk)[1] = a[i];
  88                 }
  89
  90                 a[i] = (int) (kk / 1000000000);
  91
  92                 kk -= (unsigned long long) 1000000000 * a[i];
  93         }
  94
  95         // length of quotient
  96
  97         for (i = MLENGTH(a) - 1; i > 0; i--)
  98                 if (a[i])
  99                         break;
 100
 101         MLENGTH(a) = i + 1;
 102
 103         if (little_endian())
 104                 return ((unsigned int *) &kk)[0];
 105         else
 106                 return ((unsigned int *) &kk)[1];
 107 }