diff options
Diffstat (limited to 'spec/rubyspec/core/bignum/right_shift_spec.rb')
-rw-r--r-- | spec/rubyspec/core/bignum/right_shift_spec.rb | 99 |
1 files changed, 99 insertions, 0 deletions
diff --git a/spec/rubyspec/core/bignum/right_shift_spec.rb b/spec/rubyspec/core/bignum/right_shift_spec.rb new file mode 100644 index 0000000000..d65f7c00a9 --- /dev/null +++ b/spec/rubyspec/core/bignum/right_shift_spec.rb @@ -0,0 +1,99 @@ +require File.expand_path('../../../spec_helper', __FILE__) + +describe "Bignum#>> with n >> m" do + before :each do + @bignum = bignum_value * 16 + end + + it "returns n shifted right m bits when n > 0, m > 0" do + (@bignum >> 1).should == 73786976294838206464 + end + + it "returns n shifted right m bits when n < 0, m > 0" do + (-@bignum >> 2).should == -36893488147419103232 + end + + it "respects twos complement signed shifting" do + # This explicit left hand value is important because it is the + # exact bit pattern that matters, so it's important it's right + # here to show the significance. + # + + (-42949672980000000000000 >> 14).should == -2621440001220703125 + (-42949672980000000000001 >> 14).should == -2621440001220703126 + # Note the off by one -------------------- ^^^^^^^^^^^^^^^^^^^^ + # This is because even though we discard the lowest bit, in twos + # complement it would influence the bits to the left of it. + + (-42949672980000000000000 >> 15).should == -1310720000610351563 + (-42949672980000000000001 >> 15).should == -1310720000610351563 + + (-0xfffffffffffffffff >> 32).should == -68719476736 + end + + it "respects twos complement signed shifting for very large values" do + giant = 42949672980000000000000000000000000000000000000000000000000000000000000000000000000000000000 + neg = -giant + + (giant >> 84).should == 2220446050284288846538547929770901490087453566957265138626098632812 + (neg >> 84).should == -2220446050284288846538547929770901490087453566957265138626098632813 + end + + it "returns n shifted left m bits when n > 0, m < 0" do + (@bignum >> -2).should == 590295810358705651712 + end + + it "returns n shifted left m bits when n < 0, m < 0" do + (-@bignum >> -3).should == -1180591620717411303424 + end + + it "returns n when n > 0, m == 0" do + (@bignum >> 0).should == @bignum + end + + it "returns n when n < 0, m == 0" do + (-@bignum >> 0).should == -@bignum + end + + it "returns 0 when m > 0 and m == p where 2**p > n >= 2**(p-1)" do + (@bignum >> 68).should == 0 + end + + it "returns 0 when m is a Bignum" do + (@bignum >> bignum_value).should == 0 + end + + it "returns a Fixnum == fixnum_max when (fixnum_max * 2) >> 1 and n > 0" do + result = (fixnum_max * 2) >> 1 + result.should be_an_instance_of(Fixnum) + result.should == fixnum_max + end + + it "returns a Fixnum == fixnum_min when (fixnum_min * 2) >> 1 and n < 0" do + result = (fixnum_min * 2) >> 1 + result.should be_an_instance_of(Fixnum) + result.should == fixnum_min + end + + it "calls #to_int to convert the argument to an Integer" do + obj = mock("2") + obj.should_receive(:to_int).and_return(2) + + (@bignum >> obj).should == 36893488147419103232 + end + + it "raises a TypeError when #to_int does not return an Integer" do + obj = mock("a string") + obj.should_receive(:to_int).and_return("asdf") + + lambda { @bignum >> obj }.should raise_error(TypeError) + end + + it "raises a TypeError when passed nil" do + lambda { @bignum >> nil }.should raise_error(TypeError) + end + + it "raises a TypeError when passed a String" do + lambda { @bignum >> "4" }.should raise_error(TypeError) + end +end |