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-rw-r--r--spec/rubyspec/core/bignum/right_shift_spec.rb99
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
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+++ 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