Add: Count/isPowerOf2 (#109).

oscbyspro · Oct 11, 2024 · 3379092 · 3379092
1 parent b1e7d91
commit 3379092
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Showing 3 changed files with 42 additions and 6 deletions.
diff --git a/Sources/CoreKit/Models/Count+Comparison.swift b/Sources/CoreKit/Models/Count+Comparison.swift
@@ -42,4 +42,17 @@ extension Count {
     @inlinable public var isInfinite: Bool {
         Bool(self.base.appendix)
     }
+
+    /// Indicates whether this value is a power of `2`.
+    ///
+    /// - Note: `log2(&0+1)` is the only representable infinite power of `2`.
+    ///
+    @inlinable public var isPowerOf2: Bool {
+        if  self.base.isPositive {
+            return (self.base & self.base.decremented().unchecked()).isZero
+
+        }   else {
+            return (self == Self.infinity)
+        }
+    }
 }
diff --git a/Tests/UltimathnumTests/BinaryInteger+Metadata.swift b/Tests/UltimathnumTests/BinaryInteger+Metadata.swift
@@ -37,10 +37,11 @@ import TestKit2
         whereIs(type)
 
         func whereIs<T>(_ type: T.Type) where T: BinaryInteger {
+            #expect(T.size.isPowerOf2)
             #expect(T.size >= T.Element  .size)
             #expect(T.size == T.Magnitude.size)
             #expect(T.size == T.Signitude.size)
-                        
+
             Ɣexpect(MemoryLayout<T>.self, equals: MemoryLayout<T.Magnitude>.self)
             Ɣexpect(MemoryLayout<T>.self, equals: MemoryLayout<T.Signitude>.self)
 

diff --git a/Tests/UltimathnumTests/Count+Comparison.swift b/Tests/UltimathnumTests/Count+Comparison.swift
@@ -21,6 +21,15 @@ import TestKit2
     // MARK: Tests
     //=------------------------------------------------------------------------=
 
+    @Test(arguments: fuzzers)
+    func comparisonIsLikeUnsignedIntegerComparison(_ randomness: consuming FuzzerInt) {
+        for _ in 0 ..< 256 {
+            let lhs = UX.entropic(using: &randomness)
+            let rhs = UX.entropic(using: &randomness)
+            Ɣexpect(Count(raw: lhs), equals: Count(raw: rhs), is: lhs.compared(to: rhs))
+        }
+    }
+
     @Test(arguments: fuzzers)
     func isZeroIsLikeBinaryIntegerIsZero(_ randomness: consuming FuzzerInt) {
         for _ in 0 ..< 256 {
@@ -38,11 +47,24 @@ import TestKit2
     }
 
     @Test(arguments: fuzzers)
-    func comparisonIsLikeUnsignedIntegerComparison(_ randomness: consuming FuzzerInt) {
-        for _ in 0 ..< 256 {
-            let lhs = UX.entropic(using: &randomness)
-            let rhs = UX.entropic(using: &randomness)
-            Ɣexpect(Count(raw: lhs), equals: Count(raw: rhs), is: lhs.compared(to: rhs))
+    func isPowerOf2IsNormalExceptMaxIsPowerOf2(_ randomness: consuming FuzzerInt) {
+        #expect( Count(raw: UX.max).isPowerOf2)
+        #expect(!Count(raw: IX.min).isPowerOf2)
+        #expect(!Count(raw: IX.max).isPowerOf2)
+        #expect(!Count(raw: UX.min).isPowerOf2)
+
+        for distance in 0 ..< IX(size: IX.self) - 1 {
+            #expect(Count(IX.lsb << distance).isPowerOf2)
+        }
+
+        for _ in 0 ..< conditional(debug: 64, release: 256) {
+            let random = IX.entropic(as: .natural, using: &randomness)
+            let expectation: Bool = random.count(Bit.one) == Count(01)
+            #expect(Count(random).isPowerOf2 == expectation)
+        }
+
+        for _ in 0 ..< conditional(debug: 64, release: 256) {
+            #expect(!Count(raw: IX.random(in: IX.min...IX(-2), using: &randomness)).isPowerOf2)
         }
     }
 }