ceph/src/boost/libs/multiprecision/include/boost/multiprecision/detail/float_string_cvt.hpp

   1 ///////////////////////////////////////////////////////////////
   2 //  Copyright 2013 John Maddock. Distributed under the Boost
   3 //  Software License, Version 1.0. (See accompanying file
   4 //  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_
   5 //
   6 // Generic routines for converting floating point values to and from decimal strings.
   7 // Note that these use "naive" algorithms which result in rounding error - so they
   8 // do not round trip to and from the string representation (but should only be out
   9 // in the last bit).
  10 //
  11
  12 #ifndef BOOST_MP_FLOAT_STRING_CVT_HPP
  13 #define BOOST_MP_FLOAT_STRING_CVT_HPP
  14
  15 #include <cctype>
  16
  17 namespace boost{ namespace multiprecision{ namespace detail{
  18
  19 template <class I>
  20 inline void round_string_up_at(std::string& s, int pos, I& expon)
  21 {
  22    //
  23    // Rounds up a string representation of a number at pos:
  24    //
  25    if(pos < 0)
  26    {
  27       s.insert(static_cast<std::string::size_type>(0), 1, '1');
  28       s.erase(s.size() - 1);
  29       ++expon;
  30    }
  31    else if(s[pos] == '9')
  32    {
  33       s[pos] = '0';
  34       round_string_up_at(s, pos - 1, expon);
  35    }
  36    else
  37    {
  38       if((pos == 0) && (s[pos] == '0') && (s.size() == 1))
  39          ++expon;
  40       ++s[pos];
  41    }
  42 }
  43
  44 template <class Backend>
  45 std::string convert_to_string(Backend b, std::streamsize digits, std::ios_base::fmtflags f)
  46 {
  47    using default_ops::eval_log10;
  48    using default_ops::eval_floor;
  49    using default_ops::eval_pow;
  50    using default_ops::eval_convert_to;
  51    using default_ops::eval_multiply;
  52    using default_ops::eval_divide;
  53    using default_ops::eval_subtract;
  54    using default_ops::eval_fpclassify;
  55
  56    typedef typename mpl::front<typename Backend::unsigned_types>::type ui_type;
  57    typedef typename Backend::exponent_type exponent_type;
  58
  59    std::string result;
  60    bool iszero = false;
  61    bool isneg = false;
  62    exponent_type expon = 0;
  63    std::streamsize org_digits = digits;
  64    BOOST_ASSERT(digits > 0);
  65
  66    int fpt = eval_fpclassify(b);
  67
  68    if(fpt == (int)FP_ZERO)
  69    {
  70       result = "0";
  71       iszero = true;
  72    }
  73    else if(fpt == (int)FP_INFINITE)
  74    {
  75       if(b.compare(ui_type(0)) < 0)
  76          return "-inf";
  77       else
  78          return ((f & std::ios_base::showpos) == std::ios_base::showpos) ? "+inf" : "inf";
  79    }
  80    else if(fpt == (int)FP_NAN)
  81    {
  82       return "nan";
  83    }
  84    else
  85    {
  86       //
  87       // Start by figuring out the exponent:
  88       //
  89       isneg = b.compare(ui_type(0)) < 0;
  90       if(isneg)
  91          b.negate();
  92       Backend t;
  93       Backend ten;
  94       ten = ui_type(10);
  95
  96       eval_log10(t, b);
  97       eval_floor(t, t);
  98       eval_convert_to(&expon, t);
  99       if(-expon > std::numeric_limits<number<Backend> >::max_exponent10 - 3)
 100       {
 101          int e = -expon / 2;
 102          Backend t2;
 103          eval_pow(t2, ten, e);
 104          eval_multiply(t, t2, b);
 105          eval_multiply(t, t2);
 106          if(expon & 1)
 107             eval_multiply(t, ten);
 108       }
 109       else
 110       {
 111          eval_pow(t, ten, -expon);
 112          eval_multiply(t, b);
 113       }
 114       //
 115       // Make sure we're between [1,10) and adjust if not:
 116       //
 117       if(t.compare(ui_type(1)) < 0)
 118       {
 119          eval_multiply(t, ui_type(10));
 120          --expon;
 121       }
 122       else if(t.compare(ui_type(10)) >= 0)
 123       {
 124          eval_divide(t, ui_type(10));
 125          ++expon;
 126       }
 127       Backend digit;
 128       ui_type cdigit;
 129       //
 130       // Adjust the number of digits required based on formatting options:
 131       //
 132       if(((f & std::ios_base::fixed) == std::ios_base::fixed) && (expon != -1))
 133          digits += expon + 1;
 134       if((f & std::ios_base::scientific) == std::ios_base::scientific)
 135          ++digits;
 136       //
 137       // Extract the digits one at a time:
 138       //
 139       for(unsigned i = 0; i < digits; ++i)
 140       {
 141          eval_floor(digit, t);
 142          eval_convert_to(&cdigit, digit);
 143          result += static_cast<char>('0' + cdigit);
 144          eval_subtract(t, digit);
 145          eval_multiply(t, ten);
 146       }
 147       //
 148       // Possibly round result:
 149       //
 150       if(digits >= 0)
 151       {
 152          eval_floor(digit, t);
 153          eval_convert_to(&cdigit, digit);
 154          eval_subtract(t, digit);
 155          if((cdigit == 5) && (t.compare(ui_type(0)) == 0))
 156          {
 157             // Bankers rounding:
 158             if((*result.rbegin() - '0') & 1)
 159             {
 160                round_string_up_at(result, result.size() - 1, expon);
 161             }
 162          }
 163          else if(cdigit >= 5)
 164          {
 165             round_string_up_at(result, result.size() - 1, expon);
 166          }
 167       }
 168    }
 169    while((result.size() > digits) && result.size())
 170    {
 171       // We may get here as a result of rounding...
 172       if(result.size() > 1)
 173          result.erase(result.size() - 1);
 174       else
 175       {
 176          if(expon > 0)
 177             --expon; // so we put less padding in the result.
 178          else
 179             ++expon;
 180          ++digits;
 181       }
 182    }
 183    BOOST_ASSERT(org_digits >= 0);
 184    if(isneg)
 185       result.insert(static_cast<std::string::size_type>(0), 1, '-');
 186    format_float_string(result, expon, org_digits, f, iszero);
 187
 188    return result;
 189 }
 190
 191 template <class Backend>
 192 void convert_from_string(Backend& b, const char* p)
 193 {
 194    using default_ops::eval_multiply;
 195    using default_ops::eval_add;
 196    using default_ops::eval_pow;
 197    using default_ops::eval_divide;
 198
 199    typedef typename mpl::front<typename Backend::unsigned_types>::type ui_type;
 200    b = ui_type(0);
 201    if(!p || (*p == 0))
 202       return;
 203
 204    bool is_neg = false;
 205    bool is_neg_expon = false;
 206    static const ui_type ten = ui_type(10);
 207    typename Backend::exponent_type expon = 0;
 208    int digits_seen = 0;
 209    typedef std::numeric_limits<number<Backend, et_off> > limits;
 210    static const int max_digits = limits::is_specialized ? limits::max_digits10 + 1 : INT_MAX;
 211
 212    if(*p == '+') ++p;
 213    else if(*p == '-')
 214    {
 215       is_neg = true;
 216       ++p;
 217    }
 218    if((std::strcmp(p, "nan") == 0) || (std::strcmp(p, "NaN") == 0) || (std::strcmp(p, "NAN") == 0))
 219    {
 220       eval_divide(b, ui_type(0));
 221       if(is_neg)
 222          b.negate();
 223       return;
 224    }
 225    if((std::strcmp(p, "inf") == 0) || (std::strcmp(p, "Inf") == 0) || (std::strcmp(p, "INF") == 0))
 226    {
 227       b = ui_type(1);
 228       eval_divide(b, ui_type(0));
 229       if(is_neg)
 230          b.negate();
 231       return;
 232    }
 233    //
 234    // Grab all the leading digits before the decimal point:
 235    //
 236    while(std::isdigit(*p))
 237    {
 238       eval_multiply(b, ten);
 239       eval_add(b, ui_type(*p - '0'));
 240       ++p;
 241       ++digits_seen;
 242    }
 243    if(*p == '.')
 244    {
 245       //
 246       // Grab everything after the point, stop when we've seen
 247       // enough digits, even if there are actually more available:
 248       //
 249       ++p;
 250       while(std::isdigit(*p))
 251       {
 252          eval_multiply(b, ten);
 253          eval_add(b, ui_type(*p - '0'));
 254          ++p;
 255          --expon;
 256          if(++digits_seen > max_digits)
 257             break;
 258       }
 259       while(std::isdigit(*p))
 260          ++p;
 261    }
 262    //
 263    // Parse the exponent:
 264    //
 265    if((*p == 'e') || (*p == 'E'))
 266    {
 267       ++p;
 268       if(*p == '+') ++p;
 269       else if(*p == '-')
 270       {
 271          is_neg_expon = true;
 272          ++p;
 273       }
 274       typename Backend::exponent_type e2 = 0;
 275       while(std::isdigit(*p))
 276       {
 277          e2 *= 10;
 278          e2 += (*p - '0');
 279          ++p;
 280       }
 281       if(is_neg_expon)
 282          e2 = -e2;
 283       expon += e2;
 284    }
 285    if(expon)
 286    {
 287       // Scale by 10^expon, note that 10^expon can be
 288       // outside the range of our number type, even though the
 289       // result is within range, if that looks likely, then split
 290       // the calculation in two:
 291       Backend t;
 292       t = ten;
 293       if(expon > limits::min_exponent10 + 2)
 294       {
 295          eval_pow(t, t, expon);
 296          eval_multiply(b, t);
 297       }
 298       else
 299       {
 300          eval_pow(t, t, expon + digits_seen + 1);
 301          eval_multiply(b, t);
 302          t = ten;
 303          eval_pow(t, t, -digits_seen - 1);
 304          eval_multiply(b, t);
 305       }
 306    }
 307    if(is_neg)
 308       b.negate();
 309    if(*p)
 310    {
 311       // Unexpected input in string:
 312       BOOST_THROW_EXCEPTION(std::runtime_error("Unexpected characters in string being interpreted as a float128."));
 313    }
 314 }
 315
 316 }}} // namespaces
 317
 318 #endif