-- Integer math class.
-- Can't be created, inherit from it!

indexing
  names: math;
  author: "Guichard Damien";
  created: 10,November,1995;
  modified: 10,November,1995

class MATH creation   -- empty creation clause, so can't be created.
feature {NONE}
  -- Facilities for heirs only.
  abs(n:INTEGER):INTEGER is
    -- Absolute value of n.
    do
      if n >= 0 then Result := n else Result := -n end
    end;  -- abs
  max(a,b:INTEGER):INTEGER is
    -- Maximum value of a and b.
    do
      if a >= b then Result := a else Result := b end
    end;  -- max
  min(a,b:INTEGER):INTEGER is
    -- Minimum value of a and b.
    do
      if a <= b then Result := a else Result := b end
    end;  -- min
  even(n:INTEGER):BOOLEAN is
    -- Is 'n' even?
    do
      Result := n \\ 2 = 0
    ensure -- Result = n \\ 2 = 0
    end;  -- even
  odd(n:INTEGER):BOOLEAN is
    -- Is 'n' odd?
    do
      Result := n \\ 2 = 1
    ensure -- Result = n \\ 2 = 1
    end;  -- odd
  gcd(a,b:INTEGER):INTEGER is
    -- Greater common divider of a and b.
    require -- a >= 0; b >= 0
    local c:INTEGER
    do
      from
        Result := a;
        c := b
      until Result = c
      loop
        if Result > c then
          Result := Result - c
        else
          c := c - Result
        end
      end
    end;  -- pgcd
  power(n,p:INTEGER):INTEGER is
    -- n ^ p.
    require -- p >= 0
    local i:INTEGER
    do
      if p = 0 then
        Result := 0
      else
        from
          i := 1;
          Result := n
        until i = p
        loop
          i := i + 1;
          Result := Result * n
        end
      end
    ensure -- p = 0 implies Result = 0
    end;  -- power
  faculty(n:INTEGER):INTEGER is
    -- n!
    require -- n >= 0
    do
      if n = 0 then
        Result := 1
      else
        Result := n * faculty(n-1)
      end
    end  -- faculty
end  -- class 'MATH'