proper_integer_calculation.d

module main;

import std.stdio;
import std.conv;
import std.typecons;


auto proper_div(T)(T x, T y)
{
    T q = x / y;
    if ((0 < y && x < q*y) || (y < 0 && q*y < x))
    {
        q -= 1;
    }
    return q;  
}

auto proper_mod(T)(T x, T y)
{
    return x - proper_div(x, y)*y;
}

class proper(T)
{
    private T v;
    mixin Proxy!v;
    this (T v)
    {
        this.v = v;
    }

    auto opBinary(string op:"/", S)(S y)
    {
        return proper!T(proper_div(v, cast(T)y));
    }
    auto opBinaryRight(string op:"/", S:T)(S x)
    {
        return proper!T(proper_div(cast(T)x, v));
    }
    auto opBinary(string op:"%", S)(S y)
    {
        return proper!T(proper_mod(v, cast(T)y));
    }
    auto opBinaryRight(string op:"%", S:T)(S x)
    {
        return proper!T(proper_mod(cast(T)x, v));
    }
    auto opBinary(string op, S)(S y)
    {
        return proper!T(mixin("v" ~ op ~ "cast(T)y"));
    }
    auto opBinaryRight(string op, S:T)(S x)
    {
        return proper!T(mixin("cast(T)x" ~ op ~ "v"));
    }
    auto opUnary(string op)()
    {
        if (op=="-")
        {
            return proper!T(-v);
        }
        if (op == "+")
        {
            return proper!T(v);
        }
    }
}




void test_struct()
{
    auto x = proper!long(4); // Error: template instance main.proper!(long).proper.Proxy!(v).opCall!(proper, int) error instantiating
    auto y = proper!long(3);
    writefln("x := %d; y := %d", cast(int)x, cast(int)y);
    writefln("x / y = %d", cast(int)(x / y));
    writefln("x %% y = %d", cast(int)(x % y));
    writefln("(-x) / y = %d", cast(int)((-x) / y));
    writefln("(-x) %% y = %d", cast(int)((-x) % y));
    writefln("x / (-y) = %d", cast(int)(x / (-y)));
    writefln("x %% (-y) = %d", cast(int)(x % (-y)));
    writefln("(-x) / (-y) = %d", cast(int)((-x) / (-y)));
    writefln("(-x) %% (-y) = %d", cast(int)((-x) % (-y)));
}

void main(string[] argv)
{
    test_struct();
}


struct pint // OK
{
    private int v;
    mixin Proxy!v;
    this (int v)
    {
        this.v = v;
    }

    auto opBinary(string op:"/", T)(T y)
    {
        return pint(proper_div(v, cast(int)y));
    }
    auto opBinaryRight(string op:"/", T:int)(T x)
    {
        return pint(proper_div(cast(int)x, v));
    }
    auto opBinary(string op:"%", T)(T y)
    {
        return pint(proper_mod(v, cast(int)y));
    }
    auto opBinaryRight(string op:"%", T:int)(T x)
    {
        return pint(proper_mod(cast(int)x, v));
    }
    auto opBinary(string op, T)(T y)
    {
        return pint(mixin("v" ~ op ~ "cast(int)y"));
    }
    auto opBinaryRight(string op, T:int)(T x)
    {
        return pint(mixin("cast(int)x" ~ op ~ "v"));
    }
    auto opUnary(string op)()
    {
        if (op=="-")
        {
            return pint(-v);
        }
        if (op == "+")
        {
            return pint(v);
        }
    }

}


void test_func()
{
    int x = 4;
    int y = 3;
    writefln("x := %d; y := %d", x, y);
    writefln("proper_div(x, y) = %d", proper_div(x, y)); // 1
    writefln("proper_mod(x, y) = %d", proper_mod(x, y)); // 1
    writefln("proper_div(-x, y) = %d", proper_div(-x, y)); // -2
    writefln("proper_mod(-x, y) = %d", proper_mod(-x, y)); // 2
    writefln("proper_div(x, -y) = %d", proper_div(x, -y)); // -2
    writefln("proper_mod(x, -y) = %d", proper_mod(x, -y)); // -2
    writefln("proper_div(-x, -y) = %d", proper_div(-x, -y)); // 1
    writefln("proper_mod(-x, -y) = %d", proper_mod(-x, -y)); // -1
}