1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
|
require_relative '../../spec_helper'
describe "Integer#>> (with n >> m)" do
context "fixnum" do
it "returns n shifted right m bits when n > 0, m > 0" do
(2 >> 1).should == 1
end
it "returns n shifted right m bits when n < 0, m > 0" do
(-2 >> 1).should == -1
(-7 >> 1).should == -4
(-42 >> 2).should == -11
end
it "returns n shifted left m bits when n > 0, m < 0" do
(1 >> -1).should == 2
end
it "returns n shifted left m bits when n < 0, m < 0" do
(-1 >> -1).should == -2
end
it "returns 0 when n == 0" do
(0 >> 1).should == 0
end
it "returns n when n > 0, m == 0" do
(1 >> 0).should == 1
end
it "returns n when n < 0, m == 0" do
(-1 >> 0).should == -1
end
it "returns 0 when n > 0, m > 0 and n < 2**m" do
(3 >> 2).should == 0
(7 >> 3).should == 0
(127 >> 7).should == 0
# To make sure the exponent is not truncated
(7 >> 32).should == 0
(7 >> 64).should == 0
end
it "returns -1 when n < 0, m > 0 and n > -(2**m)" do
(-3 >> 2).should == -1
(-7 >> 3).should == -1
(-127 >> 7).should == -1
# To make sure the exponent is not truncated
(-7 >> 32).should == -1
(-7 >> 64).should == -1
end
it "returns 0 when m is a bignum" do
(3 >> bignum_value).should == 0
end
it "returns an Bignum == fixnum_max * 2 when fixnum_max >> -1 and n > 0" do
result = fixnum_max >> -1
result.should be_an_instance_of(Bignum)
result.should == fixnum_max * 2
end
it "returns an Bignum == fixnum_min * 2 when fixnum_min >> -1 and n < 0" do
result = fixnum_min >> -1
result.should be_an_instance_of(Bignum)
result.should == fixnum_min * 2
end
it "calls #to_int to convert the argument to an Integer" do
obj = mock("2")
obj.should_receive(:to_int).and_return(2)
(8 >> obj).should == 2
obj = mock("to_int_bignum")
obj.should_receive(:to_int).and_return(bignum_value)
(8 >> obj).should == 0
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")
-> { 3 >> obj }.should raise_error(TypeError)
end
it "raises a TypeError when passed nil" do
-> { 3 >> nil }.should raise_error(TypeError)
end
it "raises a TypeError when passed a String" do
-> { 3 >> "4" }.should raise_error(TypeError)
end
end
context "bignum" 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")
-> { @bignum >> obj }.should raise_error(TypeError)
end
it "raises a TypeError when passed nil" do
-> { @bignum >> nil }.should raise_error(TypeError)
end
it "raises a TypeError when passed a String" do
-> { @bignum >> "4" }.should raise_error(TypeError)
end
end
end
|
