UVa/11448 - Who said crisis/bigint-2007.07.07/BigUnsignedInABase.cc

   1 /*
   2 * Matt McCutchen's Big Integer Library
   3 */
   4
   5 /*
   6 * Milan Tomic had trouble compiling this file on Microsoft
   7 * Visual C++ 6 because, in the libraries that come with
   8 * Visual C++ 6, the `std::string::push_back' method apparently
   9 * does not exist.  To get around the problem, I rewrote
  10 * `BigUnsignedInABase::operator std::string' (at the bottom
  11 * of this file) so it doesn't use `push_back'.
  12 */
  13
  14 #include "BigUnsignedInABase.hh"
  15
  16 namespace {
  17         unsigned int bitLen(unsigned int x) {
  18                 unsigned int len = 0;
  19                 while (x > 0) {
  20                         x >>= 1;
  21                         len++;
  22                 }
  23                 return len;
  24         }
  25         unsigned int ceilingDiv(unsigned int a, unsigned int b) {
  26                 return (a + b - 1) / b;
  27         }
  28 }
  29
  30 BigUnsignedInABase::BigUnsignedInABase(const BigUnsigned &x, Base base) {
  31
  32         // Check the base
  33         if (base < 2)
  34                 throw "BigUnsignedInABase(BigUnsigned, Base): The base must be at least 2";
  35         // Save the base.
  36         // This pattern is seldom seen in C++, but the analogous ``this.'' is common in Java.
  37         this->base = base;
  38
  39         // Get an upper bound on how much space we need
  40         int maxBitLenOfX = x.getLength() * BigUnsigned::N;
  41         int minBitsPerDigit = bitLen(base) - 1;
  42         int maxDigitLenOfX = ceilingDiv(maxBitLenOfX, minBitsPerDigit);
  43         len = maxDigitLenOfX; // Another change to comply with `staying in bounds'; see `BigUnsigned::divideWithRemainder'.
  44         allocate(len); // Get the space
  45
  46         BigUnsigned x2(x), buBase(base);
  47         Index digitNum = 0;
  48
  49         while (!x2.isZero()) {
  50                 // Get last digit.  This is like `lastDigit = x2 % buBase, x2 /= buBase'.
  51                 BigUnsigned lastDigit(x2);
  52                 lastDigit.divideWithRemainder(buBase, x2);
  53                 // Save the digit.
  54                 blk[digitNum] = Digit(lastDigit); // invokes `BigUnsigned ==> unsigned short' converter
  55                 // Move on.  We can't run out of room: we figured it out above.
  56                 digitNum++;
  57         }
  58
  59         // Save the actual length.
  60         len = digitNum;
  61 }
  62
  63 BigUnsignedInABase::operator BigUnsigned() const {
  64         BigUnsigned ans(0), buBase(base), temp;
  65         Index digitNum = len;
  66         while (digitNum > 0) {
  67                 digitNum--;
  68                 temp.multiply(ans, buBase);
  69                 ans.add(temp, BigUnsigned(blk[digitNum]));
  70         }
  71         return ans;
  72 }
  73
  74 BigUnsignedInABase::BigUnsignedInABase(const std::string &s, Base base) {
  75         // Check the base.
  76         if (base > 36)
  77                 throw "BigUnsignedInABase(std::string, Base): The default string conversion routines use the symbol set 0-9, A-Z and therefore support only up to base 36.  You tried a conversion with a base over 36; write your own string conversion routine.";
  78         // Save the base.
  79         // This pattern is seldom seen in C++, but the analogous ``this.'' is common in Java.
  80         this->base = base;
  81
  82         // `s.length()' is a `size_t', while `len' is a `NumberlikeArray::Index',
  83         // also known as an `unsigned int'.  Some compilers warn without this cast.
  84         len = Index(s.length());
  85         allocate(len);
  86
  87         Index digitNum, symbolNumInString;
  88         for (digitNum = 0; digitNum < len; digitNum++) {
  89                 symbolNumInString = len - 1 - digitNum;
  90                 char theSymbol = s[symbolNumInString];
  91                 if (theSymbol >= '0' && theSymbol <= '9')
  92                         blk[digitNum] = theSymbol - '0';
  93                 else if (theSymbol >= 'A' && theSymbol <= 'Z')
  94                         blk[digitNum] = theSymbol - 'A' + 10;
  95                 else if (theSymbol >= 'a' && theSymbol <= 'z')
  96                         blk[digitNum] = theSymbol - 'a' + 10;
  97                 else
  98                         throw "BigUnsignedInABase(std::string, Base): Bad symbol in input.  Only 0-9, A-Z, a-z are accepted.";
  99         }
 100         zapLeadingZeros();
 101 }
 102
 103 BigUnsignedInABase::operator std::string() const {
 104         if (base > 36)
 105                 throw "BigUnsignedInABase ==> std::string: The default string conversion routines use the symbol set 0-9, A-Z and therefore support only up to base 36.  You tried a conversion with a base over 36; write your own string conversion routine.";
 106         if (len == 0)
 107                 return std::string("0");
 108         char *s = new char[len + 1];
 109         s[len] = '\0';
 110         Index digitNum, symbolNumInString;
 111         for (symbolNumInString = 0; symbolNumInString < len; symbolNumInString++) {
 112                 digitNum = len - 1 - symbolNumInString;
 113                 Digit theDigit = blk[digitNum];
 114                 if (theDigit < 10)
 115                         s[symbolNumInString] = char('0' + theDigit);
 116                 else
 117                         s[symbolNumInString] = char('A' + theDigit - 10);
 118         }
 119         std::string s2(s);
 120         // 2006.05.03: This needs to be [] to match the allocation
 121         delete [] s;
 122         return s2;
 123 }