Chris@16: ///////////////////////////////////////////////////////////////
Chris@16: //  Copyright 2013 John Maddock. Distributed under the Boost
Chris@16: //  Software License, Version 1.0. (See accompanying file
Chris@16: //  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_
Chris@16: //
Chris@16: // Generic routines for converting floating point values to and from decimal strings.
Chris@16: // Note that these use "naive" algorithms which result in rounding error - so they
Chris@16: // do not round trip to and from the string representation (but should only be out
Chris@16: // in the last bit).
Chris@16: //
Chris@16: 
Chris@16: #ifndef BOOST_MP_FLOAT_STRING_CVT_HPP
Chris@16: #define BOOST_MP_FLOAT_STRING_CVT_HPP
Chris@16: 
Chris@16: #include <cctype>
Chris@16: 
Chris@16: namespace boost{ namespace multiprecision{ namespace detail{
Chris@16: 
Chris@101: template <class I>
Chris@101: inline void round_string_up_at(std::string& s, int pos, I& expon)
Chris@16: {
Chris@16:    //
Chris@16:    // Rounds up a string representation of a number at pos:
Chris@16:    //
Chris@16:    if(pos < 0)
Chris@16:    {
Chris@101:       s.insert(static_cast<std::string::size_type>(0), 1, '1');
Chris@16:       s.erase(s.size() - 1);
Chris@16:       ++expon;
Chris@16:    }
Chris@16:    else if(s[pos] == '9')
Chris@16:    {
Chris@16:       s[pos] = '0';
Chris@16:       round_string_up_at(s, pos - 1, expon);
Chris@16:    }
Chris@16:    else
Chris@16:    {
Chris@16:       if((pos == 0) && (s[pos] == '0') && (s.size() == 1))
Chris@16:          ++expon;
Chris@16:       ++s[pos];
Chris@16:    }
Chris@16: }
Chris@16: 
Chris@16: template <class Backend>
Chris@16: std::string convert_to_string(Backend b, std::streamsize digits, std::ios_base::fmtflags f)
Chris@16: {
Chris@16:    using default_ops::eval_log10;
Chris@16:    using default_ops::eval_floor;
Chris@16:    using default_ops::eval_pow;
Chris@16:    using default_ops::eval_convert_to;
Chris@16:    using default_ops::eval_multiply;
Chris@16:    using default_ops::eval_divide;
Chris@16:    using default_ops::eval_subtract;
Chris@16:    using default_ops::eval_fpclassify;
Chris@16: 
Chris@16:    typedef typename mpl::front<typename Backend::unsigned_types>::type ui_type;
Chris@16:    typedef typename Backend::exponent_type exponent_type;
Chris@16: 
Chris@16:    std::string result;
Chris@16:    bool iszero = false;
Chris@16:    bool isneg = false;
Chris@16:    exponent_type expon = 0;
Chris@16:    std::streamsize org_digits = digits;
Chris@16:    BOOST_ASSERT(digits > 0);
Chris@16: 
Chris@16:    int fpt = eval_fpclassify(b);
Chris@16: 
Chris@101:    if(fpt == (int)FP_ZERO)
Chris@16:    {
Chris@16:       result = "0";
Chris@16:       iszero = true;
Chris@16:    }
Chris@101:    else if(fpt == (int)FP_INFINITE)
Chris@16:    {
Chris@16:       if(b.compare(ui_type(0)) < 0)
Chris@16:          return "-inf";
Chris@16:       else
Chris@16:          return ((f & std::ios_base::showpos) == std::ios_base::showpos) ? "+inf" : "inf";
Chris@16:    }
Chris@101:    else if(fpt == (int)FP_NAN)
Chris@16:    {
Chris@16:       return "nan";
Chris@16:    }
Chris@16:    else
Chris@16:    {
Chris@16:       //
Chris@16:       // Start by figuring out the exponent:
Chris@16:       //
Chris@16:       isneg = b.compare(ui_type(0)) < 0;
Chris@16:       if(isneg)
Chris@16:          b.negate();
Chris@16:       Backend t;
Chris@16:       Backend ten;
Chris@16:       ten = ui_type(10);
Chris@16: 
Chris@16:       eval_log10(t, b);
Chris@16:       eval_floor(t, t);
Chris@16:       eval_convert_to(&expon, t);
Chris@16:       if(-expon > std::numeric_limits<number<Backend> >::max_exponent10 - 3)
Chris@16:       {
Chris@16:          int e = -expon / 2;
Chris@16:          Backend t2;
Chris@16:          eval_pow(t2, ten, e);
Chris@16:          eval_multiply(t, t2, b);
Chris@16:          eval_multiply(t, t2);
Chris@16:          if(expon & 1)
Chris@16:             eval_multiply(t, ten);
Chris@16:       }
Chris@16:       else
Chris@16:       {
Chris@16:          eval_pow(t, ten, -expon);
Chris@16:          eval_multiply(t, b);
Chris@16:       }
Chris@16:       //
Chris@16:       // Make sure we're between [1,10) and adjust if not:
Chris@16:       //
Chris@16:       if(t.compare(ui_type(1)) < 0)
Chris@16:       {
Chris@16:          eval_multiply(t, ui_type(10));
Chris@16:          --expon;
Chris@16:       }
Chris@16:       else if(t.compare(ui_type(10)) >= 0)
Chris@16:       {
Chris@16:          eval_divide(t, ui_type(10));
Chris@16:          ++expon;
Chris@16:       }
Chris@16:       Backend digit;
Chris@16:       ui_type cdigit;
Chris@16:       //
Chris@16:       // Adjust the number of digits required based on formatting options:
Chris@16:       //
Chris@16:       if(((f & std::ios_base::fixed) == std::ios_base::fixed) && (expon != -1))
Chris@16:          digits += expon + 1;
Chris@16:       if((f & std::ios_base::scientific) == std::ios_base::scientific)
Chris@16:          ++digits;
Chris@16:       //
Chris@16:       // Extract the digits one at a time:
Chris@16:       //
Chris@16:       for(unsigned i = 0; i < digits; ++i)
Chris@16:       {
Chris@16:          eval_floor(digit, t);
Chris@16:          eval_convert_to(&cdigit, digit);
Chris@16:          result += static_cast<char>('0' + cdigit);
Chris@16:          eval_subtract(t, digit);
Chris@16:          eval_multiply(t, ten);
Chris@16:       }
Chris@16:       //
Chris@16:       // Possibly round result:
Chris@16:       //
Chris@16:       if(digits >= 0)
Chris@16:       {
Chris@16:          eval_floor(digit, t);
Chris@16:          eval_convert_to(&cdigit, digit);
Chris@16:          eval_subtract(t, digit);
Chris@16:          if((cdigit == 5) && (t.compare(ui_type(0)) == 0))
Chris@16:          {
Chris@16:             // Bankers rounding:
Chris@16:             if((*result.rbegin() - '0') & 1)
Chris@16:             {
Chris@16:                round_string_up_at(result, result.size() - 1, expon);
Chris@16:             }
Chris@16:          }
Chris@16:          else if(cdigit >= 5)
Chris@16:          {
Chris@16:             round_string_up_at(result, result.size() - 1, expon);
Chris@16:          }
Chris@16:       }
Chris@16:    }
Chris@16:    while((result.size() > digits) && result.size())
Chris@16:    {
Chris@16:       // We may get here as a result of rounding...
Chris@16:       if(result.size() > 1)
Chris@16:          result.erase(result.size() - 1);
Chris@16:       else
Chris@16:       {
Chris@16:          if(expon > 0)
Chris@16:             --expon; // so we put less padding in the result.
Chris@16:          else
Chris@16:             ++expon;
Chris@16:          ++digits;
Chris@16:       }
Chris@16:    }
Chris@16:    BOOST_ASSERT(org_digits >= 0);
Chris@16:    if(isneg)
Chris@101:       result.insert(static_cast<std::string::size_type>(0), 1, '-');
Chris@16:    format_float_string(result, expon, org_digits, f, iszero);
Chris@16: 
Chris@16:    return result;
Chris@16: }
Chris@16: 
Chris@16: template <class Backend>
Chris@16: void convert_from_string(Backend& b, const char* p)
Chris@16: {
Chris@16:    using default_ops::eval_multiply;
Chris@16:    using default_ops::eval_add;
Chris@16:    using default_ops::eval_pow;
Chris@16:    using default_ops::eval_divide;
Chris@16: 
Chris@16:    typedef typename mpl::front<typename Backend::unsigned_types>::type ui_type;
Chris@16:    b = ui_type(0);
Chris@16:    if(!p || (*p == 0))
Chris@16:       return;
Chris@16: 
Chris@16:    bool is_neg = false;
Chris@16:    bool is_neg_expon = false;
Chris@16:    static const ui_type ten = ui_type(10);
Chris@16:    typename Backend::exponent_type expon = 0;
Chris@16:    int digits_seen = 0;
Chris@16:    typedef std::numeric_limits<number<Backend, et_off> > limits;
Chris@16:    static const int max_digits = limits::is_specialized ? limits::max_digits10 + 1 : INT_MAX;
Chris@16: 
Chris@16:    if(*p == '+') ++p;
Chris@16:    else if(*p == '-')
Chris@16:    {
Chris@16:       is_neg = true;
Chris@16:       ++p;
Chris@16:    }
Chris@16:    if((std::strcmp(p, "nan") == 0) || (std::strcmp(p, "NaN") == 0) || (std::strcmp(p, "NAN") == 0))
Chris@16:    {
Chris@16:       eval_divide(b, ui_type(0));
Chris@16:       if(is_neg)
Chris@16:          b.negate();
Chris@16:       return;
Chris@16:    }
Chris@16:    if((std::strcmp(p, "inf") == 0) || (std::strcmp(p, "Inf") == 0) || (std::strcmp(p, "INF") == 0))
Chris@16:    {
Chris@16:       b = ui_type(1);
Chris@16:       eval_divide(b, ui_type(0));
Chris@16:       if(is_neg)
Chris@16:          b.negate();
Chris@16:       return;
Chris@16:    }
Chris@16:    //
Chris@16:    // Grab all the leading digits before the decimal point:
Chris@16:    //
Chris@16:    while(std::isdigit(*p))
Chris@16:    {
Chris@16:       eval_multiply(b, ten);
Chris@16:       eval_add(b, ui_type(*p - '0'));
Chris@16:       ++p;
Chris@16:       ++digits_seen;
Chris@16:    }
Chris@16:    if(*p == '.')
Chris@16:    {
Chris@16:       //
Chris@16:       // Grab everything after the point, stop when we've seen
Chris@16:       // enough digits, even if there are actually more available:
Chris@16:       //
Chris@16:       ++p;
Chris@16:       while(std::isdigit(*p))
Chris@16:       {
Chris@16:          eval_multiply(b, ten);
Chris@16:          eval_add(b, ui_type(*p - '0'));
Chris@16:          ++p;
Chris@16:          --expon;
Chris@16:          if(++digits_seen > max_digits)
Chris@16:             break;
Chris@16:       }
Chris@16:       while(std::isdigit(*p))
Chris@16:          ++p;
Chris@16:    }
Chris@16:    //
Chris@16:    // Parse the exponent:
Chris@16:    //
Chris@16:    if((*p == 'e') || (*p == 'E'))
Chris@16:    {
Chris@16:       ++p;
Chris@16:       if(*p == '+') ++p;
Chris@16:       else if(*p == '-')
Chris@16:       {
Chris@16:          is_neg_expon = true;
Chris@16:          ++p;
Chris@16:       }
Chris@16:       typename Backend::exponent_type e2 = 0;
Chris@16:       while(std::isdigit(*p))
Chris@16:       {
Chris@16:          e2 *= 10;
Chris@16:          e2 += (*p - '0');
Chris@16:          ++p;
Chris@16:       }
Chris@16:       if(is_neg_expon)
Chris@16:          e2 = -e2;
Chris@16:       expon += e2;
Chris@16:    }
Chris@16:    if(expon)
Chris@16:    {
Chris@16:       // Scale by 10^expon, note that 10^expon can be
Chris@16:       // outside the range of our number type, even though the
Chris@16:       // result is within range, if that looks likely, then split
Chris@16:       // the calculation in two:
Chris@16:       Backend t;
Chris@16:       t = ten;
Chris@16:       if(expon > limits::min_exponent10 + 2)
Chris@16:       {
Chris@16:          eval_pow(t, t, expon);
Chris@16:          eval_multiply(b, t);
Chris@16:       }
Chris@16:       else
Chris@16:       {
Chris@16:          eval_pow(t, t, expon + digits_seen + 1);
Chris@16:          eval_multiply(b, t);
Chris@16:          t = ten;
Chris@16:          eval_pow(t, t, -digits_seen - 1);
Chris@16:          eval_multiply(b, t);
Chris@16:       }
Chris@16:    }
Chris@16:    if(is_neg)
Chris@16:       b.negate();
Chris@16:    if(*p)
Chris@16:    {
Chris@16:       // Unexpected input in string:
Chris@16:       BOOST_THROW_EXCEPTION(std::runtime_error("Unexpected characters in string being interpreted as a float128."));
Chris@16:    }
Chris@16: }
Chris@16: 
Chris@16: }}} // namespaces
Chris@16: 
Chris@16: #endif