Hi,
here is my solution and some unit tests.
(I didn’t know that it’s possible to write a block with an array
argument,
as in “define_method meth do |*other|”. That’s a nice feature.)
Regards,
Boris
c_int.rb
class UnsignedFixedWidthInt
def initialize(value, bits)
raise ArgumentError.new(‘number of bits must be > 0’) if bits <= 0
@bits = bits
@value = value % 2**@bits
end
operators returning a new FixedWidthInt
%w{& ^ | << >> + - * / +@ -@ ~@}.each do |operator|
define_method operator do |*other|
self.class.new(@value.send(operator, *other), @bits)
end
end
methods forwarded to @value
%w{== < > <=> inspect to_s to_i to_int}.each do |meth|
define_method meth do |*other|
@value.send(meth, *other)
end
end
def coerce(other)
Integer == other ? [other, @value] : [Float(other), Float(@value)]
end
end
class SignedFixedWidthInt < UnsignedFixedWidthInt
def initialize(value, bits)
super(value, bits)
# value is negative if MSB is set:
@value -= 2**@bits if @value[@bits - 1] == 1
end
end
c_int_test.rb
require ‘c_int’
require ‘test/unit’
class CIntTest < Test::Unit::TestCase
def test_no_bits
assert_raises(ArgumentError) { UnsignedFixedWidthInt.new(0, 0) }
assert_raises(ArgumentError) { UnsignedFixedWidthInt.new(0, -1) }
end
def test_one_bit
n = UnsignedFixedWidthInt.new(0xFF, 1)
assert_equal 1, n
n += 1
assert_equal 0, n
n = SignedFixedWidthInt.new(0xFF, 1)
assert_equal(-1, n)
n += 1
assert_equal 0, n
n += 1
assert_equal(-1, n)
end
def test_unsigned
n = UnsignedFixedWidthInt.new(0xFF, 8)
assert_equal 255, n
n += 2
assert_equal 1, n
n = n << 1
assert_equal 2, n
n = n >> 1
assert_equal 1, n
assert_equal 254, (~n)
n += 12
assert_equal 13, n
n = n & 0x0E
assert_equal 12, n
n = n * 24
assert_equal 32, n
n = n / 15
assert_equal 2, n
end
def test_signed
n = SignedFixedWidthInt.new(0x01, 8)
assert_equal 1, n
n = n << 7
assert_equal(-128, n)
n -= 1
assert_equal 127, n
n = n >> 6
assert_equal 1, n
n -= 2
assert_equal(-1, n)
n = n ^ 0xF3
assert_equal 12, n
n = n | 0x01
assert_equal 13, n
n = +n
assert_equal 13, n
n = -n
assert_equal(-13, n)
end
def test_too_wide
n = UnsignedFixedWidthInt.new(0x0, 8)
n += 0xFFEE
assert_equal 238, n
end
def test_signed_shift_right
n = SignedFixedWidthInt.new(0x80, 8)
n = n >> 1
assert_equal(-64, n) # with sign extension
end
def test_equal
s1 = SignedFixedWidthInt.new(-1, 4)
s2 = SignedFixedWidthInt.new(-1, 4)
s3 = SignedFixedWidthInt.new(1, 4)
u1 = UnsignedFixedWidthInt.new(1, 4)
u2 = UnsignedFixedWidthInt.new(1, 4)
assert u1 != s1
assert s1 != s3
assert u1 == u2
assert s1 == s2
assert s3 == u1
assert(-1 == s1)
assert s1 == -1
end
def test_conversions
n = SignedFixedWidthInt.new(-100, 7)
assert “-100”, n.to_s
assert “-100”, n.inspect
assert(-100, n.to_i)
assert(-100, n.to_int)
end
def test_coerce
n = UnsignedFixedWidthInt.new(1, 4)
assert 1.1 > n
assert 0.9 < n
assert 1 == n
end
def test_comparison
s = SignedFixedWidthInt.new(-1, 4)
u = UnsignedFixedWidthInt.new(1, 4)
assert u > s
assert s < u
assert s < 0
assert u > 0
assert 0 > s
assert 0 < u
assert_equal(-1, s <=> u)
assert_equal 1, u <=> s
assert_equal 0, 1 <=> u
assert_equal 0, -1 <=> s
end
end
However, it is planned for the Ruby Q. 2.0 site,