nxt.math_ex source code

1 module nxt.math_ex;
2 
3 import std.traits : isIntegral, isUnsigned, isNumeric;
4 
5 /** Check if `x` is an exact (binary) power of 2.
6  *
7  * See_Also: http://forum.dlang.org/thread/zumhmosfkvwjymjhmtlt@forum.dlang.org#post-fvnmurrctavpfkunssdf:40forum.dlang.org
8  * See_Also: http://forum.dlang.org/post/hloonbgclzloqemycnth@forum.dlang.org
9 */
10 bool isPow2(T)(T x)
11     if (isNumeric!T)
12 {
13     import std.math : isPowerOf2; // https://github.com/dlang/phobos/pull/4327/files
14     return isPowerOf2(x);
15 }
16 alias isPowerOf2 = isPow2;
17 /// ditto
18 bool isPow2A(T)(T x) if (isIntegral!T)
19 {
20     return x && !(x & (x - 1));
21 }
22 /// ditto
23 bool isPow2B(T)(T x) if (isIntegral!T)
24 {
25     return (x & -x) > (x - 1);
26 }
27 /// ditto
28 bool isPow2D(T)(T x) if (isIntegral!T)
29 {
30     return (x > 0) && !(x & (x - 1));
31 }
32 /// ditto, avoids a jump instruction.
33 bool isPow2E(T)(T x) if (isIntegral!T)
34 {
35     return (x > 0) & !(x & (x - 1));
36 }
37 /// ditto
38 bool isPow2F(T)(T x) if (isIntegral!T)
39 {
40     return (x & -x) > (x >>> 1);
41 }
42 
43 ///
44 @safe pure nothrow @nogc unittest
45 {
46     import std.meta : AliasSeq;
47     foreach (fn; AliasSeq!(isPow2, isPow2A, isPow2D, isPow2E, isPow2F))
48     {
49         // run-time
50         assert(!fn(7));
51         assert(fn(8));
52         assert(!fn(9));
53 
54         // compile-time
55         static assert(!fn(7));
56         static assert(fn(8));
57         static assert(!fn(9));
58 
59         assert(!fn(0));
60         assert(fn(1));
61         assert(fn(2));
62         assert(!fn(3));
63         assert(fn(4));
64         assert(!fn(5));
65         assert(!fn(6));
66         assert(!fn(7));
67         assert(fn(8));
68     }
69 }
70 
71 /** Check if `x` is an exact (binary) power of 2, except when `x` is zero then
72  * zero is returned.
73  *
74  * See_Also: http://forum.dlang.org/thread/zumhmosfkvwjymjhmtlt@forum.dlang.org#post-fvnmurrctavpfkunssdf:40forum.dlang.org
75  * See_Also: http://forum.dlang.org/post/hloonbgclzloqemycnth@forum.dlang.org
76 */
77 bool isPow2fast(T)(T x)
78 if (isUnsigned!T)
79 {
80     return (x & (x - 1)) == 0;
81 }
82 
83 @safe pure nothrow @nogc unittest
84 {
85     import std.meta : AliasSeq;
86     foreach (fn; AliasSeq!(isPow2fast))
87     {
88         // run-time
89         assert(!fn(7U));
90         assert(fn(8U));
91         assert(!fn(9U));
92 
93         // compile-time
94         static assert(!fn(7U));
95         static assert(fn(8U));
96         static assert(!fn(9U));
97 
98         assert(fn(1U));
99         assert(fn(2U));
100         assert(!fn(3U));
101         assert(fn(4U));
102         assert(!fn(5U));
103         assert(!fn(6U));
104         assert(!fn(7U));
105         assert(fn(8U));
106     }
107 }