liblogintpack.h

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#ifndef liblogintpack_h
#define liblogintpack_h

#include <cmath>

namespace logintpack
{
        constexpr int8_t smallestPositive = 0;
        // note that abs(unpack(smallestNegative)) == unpack(1), i.e. there
        // is no "x" such that "unpack(x) == -unpack(0)"
        constexpr int8_t smallestNegative = -1;

        int8_t pack8logCeil(double x,double lmin, double lmax, uint8_t base=128)
        {
                if(base>128) base=128;
                const double l = std::log(std::abs(x));
                const double centered = (l-lmin)/(lmax-lmin)*base;
                int8_t  r=std::ceil(centered);
                if(centered >= base-1) r=base-1;
                if(centered < 0) r=0;
                if(x<0) r = r==0 ? -1 : -r;
                return r;
        }

    int8_t pack8log(double x,double lmin, double lmax, uint8_t base=128)
    {
            if(base>128) base=128;
        const double l = std::log(std::abs(x));
        const double centered = (l-lmin)/(lmax-lmin)*base;
        int8_t  r=centered;
        if(centered >= base-1) r=base-1;
        if(centered < 0) r=0;
        if(x<0) r = r==0 ? -1 : -r;
        return r;
    }

    int8_t pack8logClosed(double x,double lmin, double lmax, uint8_t base=128)
    {
            if(base>128) base=128;
        const double l = std::log(std::abs(x));
        const double centered = (l-lmin)/(lmax-lmin)*(base-1);
        int8_t  r=round(centered);
        if(centered >= base-1) r=base-1;
        if(centered < 0) r=0;
        if(x<0) r = r==0 ? -1 : -r;
        return r;
    }


    double unpack8log(int8_t i,double lmin, double lmax, uint8_t base=128)
    {
            if(base>128) base=128;
            const double basef=base;
        const double l=lmin+std::abs(i)/basef*(lmax-lmin);
        const double val=std::exp(l);
        if(i<0) return -val; else return val;
    }

    double unpack8logClosed(int8_t i,double lmin, double lmax, uint8_t base=128)
    {
            if(base>128) base=128;
            const double basef=base-1;
        double l=lmin+std::abs(i)/basef*(lmax-lmin);
        if (std::abs(i) == base-1) l = lmax;
        const double val=std::exp(l);
        if(i<0) return -val; else return val;
    }

}
#endif