文字列をRubyっぽく数値（浮動小数）変換する

整数変換を作ったついでに浮動小数も作ってみた。

整数変換の方は整理できたけど、こっちは落書きみたいだ・・・

float.cpp

namespace Float {

    double base(double direction, int volume)
    {
        double position = 1.0;
        for(int i = 0; i < volume; ++i)
        {
            position *= direction;
        }
        return position;
    }

    double to_f(const char* itr, const char* end)
    {
        if(itr == end){ return 0.0; } // NG

        double flag = 1.0;
        switch(*itr)
        {
        case '-':
            flag = -1.0;
            // no break needed
        case '+':
            while(true)
            {
                ++itr;
                if(itr == end){ return 0.0; } // NG
                if(*itr != ' '){ break; }
            }
            break;
        }

        double mantissa = 0.0;

        if(Integer::DecimalNumber::acceptable(*itr))
        {
            mantissa = Integer::DecimalNumber::to_i(*itr);
            while(true)
            {
                ++itr;
                if(itr == end){ return flag * mantissa; } // OK
                if(*itr == '_')
                {
                    ++itr;
                    if(itr == end){ return flag * mantissa; } // OK (with garbage)
                }
                if(!Integer::DecimalNumber::acceptable(*itr))
                {
                    break;
                }
                mantissa = mantissa * 10.0 + Integer::DecimalNumber::to_i(*itr);
            }
        }

        if('.' == *itr)
        {
            ++itr;
            if(itr == end){ return flag * mantissa; } // OK (with garbage)

            if(!Integer::DecimalNumber::acceptable(*itr))
            {
                return flag * mantissa; // OK (with garbage)
            }

            double position = 0.1;
            while(true)
            {
                mantissa += position * Integer::DecimalNumber::to_i(*itr);
                ++itr;
                if(itr == end){ break; }
                if('_' == *itr)
                {
                    ++itr;
                    if(itr == end){ break; }
                }
                if(!Integer::DecimalNumber::acceptable(*itr)){ break; }
                position *= 0.1;
            }
        }

        if('e' != *itr && 'E' != *itr){ return flag * mantissa; }

        ++itr;
        if(itr == end){ return flag * mantissa; }

        if('-' == *itr)
            return flag * mantissa * base(0.1, Integer::parse_first<Integer::DecimalNumber>(itr, end));

        if('+' == *itr)
            return flag * mantissa * base(10.0, Integer::parse_first<Integer::DecimalNumber>(itr, end));
        
        if(Integer::DecimalNumber::acceptable(*itr))
            return flag * mantissa * base(10.0, Integer::parse_last<Integer::DecimalNumber>(itr, end));

        return flag * mantissa;
    }
}