ranged_int

-module(ranged_int@internal@limit).
-compile([no_auto_import, nowarn_unused_vars, nowarn_unused_function, nowarn_nomatch]).

-export([check_limits/3]).
-export_type([limit/0, limit_check/0]).

-type limit() :: {bounded, bigi:big_int()} | unbounded.

-type limit_check() :: no_overflow |
    {overflow, bigi:big_int()} |
    {underflow, bigi:big_int()}.

-spec diff(limit(), bigi:big_int()) -> bigi:big_int().
diff(Limit, Value) ->
    case Limit of
        unbounded ->
            bigi_ffi:zero();

        {bounded, Lim} ->
            bigi_ffi:subtract(Value, Lim)
    end.

-spec check_limits(bigi:big_int(), limit(), limit()) -> limit_check().
check_limits(Value, Min, Max) ->
    Max_diff = diff(Max, Value),
    case bigi_ffi:compare(bigi_ffi:zero(), Max_diff) of
        gt ->
            {overflow, Max_diff};

        eq ->
            Min_diff = diff(Min, Value),
            case bigi_ffi:compare(bigi_ffi:zero(), Min_diff) of
                lt ->
                    {underflow, bigi_ffi:multiply(Min_diff, bigi_ffi:from(-1))};

                eq ->
                    no_overflow;

                gt ->
                    no_overflow
            end;

        lt ->
            Min_diff = diff(Min, Value),
            case bigi_ffi:compare(bigi_ffi:zero(), Min_diff) of
                lt ->
                    {underflow, bigi_ffi:multiply(Min_diff, bigi_ffi:from(-1))};

                eq ->
                    no_overflow;

                gt ->
                    no_overflow
            end
    end.