Is power of two

math/binarymath/arithmeticmean.go → math/binary/arithmeticmean.go

@@ -5,8 +5,8 @@
 // author(s) [red_byte](https://github.com/i-redbyte)
 // see arithmeticmean_test.go
 
-// Package binarymath describes algorithms that use binary operations for different calculations.
-package binarymath
+// Package binary describes algorithms that use binary operations for different calculations.
+package binary
 
 func MeanUsingAndXor(a int, b int) int {
 	return ((a ^ b) >> 1) + (a & b)

math/binarymath/arithmeticmean_test.go → math/binary/arithmeticmean_test.go

@@ -3,7 +3,7 @@
 // author(s) [red_byte](https://github.com/i-redbyte)
 // see arithmeticmean.go
 
-package binarymath
+package binary
 
 import "testing"
 

math/binary/checkisnumberpoweroftwo.go

@@ -0,0 +1,36 @@
+// checkisnumberpoweroftwo.go
+// description: Is the number a power of two
+// details:
+// Checks if a number is a power of two- [Power of two](https://en.wikipedia.org/wiki/Power_of_two)
+// author(s) [red_byte](https://github.com/i-redbyte)
+// see checkisnumberpoweroftwo_test.go
+
+package binary
+
+// IsPowerOfTwo This function uses the fact that powers of 2 are represented
+// like 10...0 in binary, and numbers one less than the power of 2
+// are represented like 11...1.
+// Therefore, using the and function:
+//    10...0
+//  & 01...1
+//    00...0 -> 0
+// This is also true for 0, which is not a power of 2, for which we
+// have to add and extra condition.
+func IsPowerOfTwo(x int) bool {
+	return x > 0 && (x&(x-1)) == 0
+}
+
+// IsPowerOfTwoLeftShift This function takes advantage of the fact that left shifting a number
+// by 1 is equivalent to multiplying by 2. For example, binary 00000001 when shifted by 3 becomes 00001000,
+// which in decimal system is 8 or = 2 * 2 * 2
+func IsPowerOfTwoLeftShift(number uint) bool {
+	if number == 0 {
+		return false
+	}
+	for p := uint(1); p > 0; p = p << 1 {
+		if number == p {
+			return true
+		}
+	}
+	return false
+}

math/binary/checkisnumberpoweroftwo_test.go

@@ -0,0 +1,93 @@
+// checkisnumberpoweroftwo_test.go
+// description: Test for Is the number a power of two
+// author(s) [red_byte](https://github.com/i-redbyte)
+// see checkisnumberpoweroftwo.go
+
+package binary
+
+import (
+	math2 "github.com/TheAlgorithms/Go/math"
+	"math"
+	"testing"
+)
+
+func getTestsForPowerOfTwo() []struct {
+	name    string
+	a       int
+	missing bool
+} {
+	var tests = []struct {
+		name    string
+		a       int
+		missing bool
+	}{
+		{"Is 64 a power of 2? - YES", 64, true},
+		{"Is 1 a power of 2? - YES", 1, true},
+		{"Is 2 a power of 2? - YES", 2, true},
+		{"Is 5 a power of 2? - NO", 5, false},
+		{"Is 1023 a power of 2? - NO", 1023, false},
+		{"Is 1024 a power of 2? - YES", 1024, true},
+		{"Is 0 a power of 2? - NO", 0, false},
+		{"Is 9223372036854775807 a power of 2? - NO", math.MaxInt64, false},
+		{"Is 9223372036854775806 a power of 2? - NO", math.MaxInt64, false},
+		{"Is 4611686018427387904 a power of 2? - YES", 4611686018427387904, true},
+	}
+	return tests
+}
+
+func TestIsPowerOfTwo(t *testing.T) {
+	tests := getTestsForPowerOfTwo()
+	for _, tv := range tests {
+		t.Run(tv.name, func(t *testing.T) {
+			result := IsPowerOfTwo(tv.a)
+			t.Log(tv.a, " ", result)
+			if result != tv.missing {
+				t.Errorf("Wrong result! Expected:%v, returned:%v ", tv.missing, result)
+			}
+		})
+	}
+}
+
+func TestIsPowerOfTwoLeftShift(t *testing.T) {
+	tests := getTestsForPowerOfTwo()
+	for _, tv := range tests {
+		t.Run(tv.name, func(t *testing.T) {
+			result := IsPowerOfTwoLeftShift(uint(tv.a))
+			t.Log(tv.a, " ", result)
+			if result != tv.missing {
+				t.Errorf("Wrong result! Expected:%v, returned:%v ", tv.missing, result)
+			}
+		})
+	}
+}
+
+func TestIsPowOfTwoUseLog(t *testing.T) {
+	tests := getTestsForPowerOfTwo()
+	for _, tv := range tests {
+		t.Run(tv.name, func(t *testing.T) {
+			result := math2.IsPowOfTwoUseLog(float64(tv.a))
+			t.Log(tv.a, " ", result)
+			if result != tv.missing {
+				t.Errorf("Wrong result! Expected:%v, returned:%v ", tv.missing, result)
+			}
+		})
+	}
+}
+
+func BenchmarkIsPowerOfTwoBinaryMethod(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		IsPowerOfTwo(1024)
+	}
+}
+
+func BenchmarkIsPowerOfTwoUseCycleAndLeftShift(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		IsPowerOfTwoLeftShift(1024)
+	}
+}
+
+func BenchmarkIsPowerOfTwoUseLog(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		math2.IsPowOfTwoUseLog(1024)
+	}
+}

math/binarymath/xorsearch.go → math/binary/xorsearch.go

@@ -5,7 +5,7 @@
 // author(s) [red_byte](https://github.com/i-redbyte)
 // see xorsearch_test.go
 
-package binarymath
+package binary
 
 func XorSearchMissingNumber(a []int) int {
 	n := len(a)

math/binarymath/xorsearch_test.go → math/binary/xorsearch_test.go

@@ -2,7 +2,7 @@
 // description: Test for Find a missing number in a sequence
 // author(s) [red_byte](https://github.com/i-redbyte)
 // see xorsearch.go
-package binarymath
+package binary
 
 import (
 	"testing"

math/checkisnumberpoweroftwo.go

@@ -0,0 +1,16 @@
+package math
+
+import (
+	"math"
+)
+
+// IsPowOfTwoUseLog This function checks if a number is a power of two using the logarithm.
+// The limiting degree can be from 0 to 63.
+// See alternatives in the binary package.
+func IsPowOfTwoUseLog(number float64) bool {
+	if number == 0 || math.Round(number) == math.MaxInt64 {
+		return false
+	}
+	log := math.Log2(number)
+	return log == math.Round(log)
+}

math/checkisnumberpoweroftwo_test.go

@@ -0,0 +1,54 @@
+// checkisnumberpoweroftwo_test.go
+// description: Test for Is the number a power of two
+// author(s) [red_byte](https://github.com/i-redbyte)
+// see checkisnumberpoweroftwo.go
+
+package math
+
+import (
+	"math"
+	"testing"
+)
+
+func getTestsForPowerOfTwo() []struct {
+	name    string
+	a       int
+	missing bool
+} {
+	var tests = []struct {
+		name    string
+		a       int
+		missing bool
+	}{
+		{"Is 64 a power of 2? - YES", 64, true},
+		{"Is 1 a power of 2? - YES", 1, true},
+		{"Is 2 a power of 2? - YES", 2, true},
+		{"Is 5 a power of 2? - NO", 5, false},
+		{"Is 1023 a power of 2? - NO", 1023, false},
+		{"Is 1024 a power of 2? - YES", 1024, true},
+		{"Is 0 a power of 2? - NO", 0, false},
+		{"Is 9223372036854775807 a power of 2? - NO", math.MaxInt64, false},
+		{"Is 9223372036854775806 a power of 2? - NO", math.MaxInt64, false},
+		{"Is 4611686018427387904 a power of 2? - YES", 4611686018427387904, true},
+	}
+	return tests
+}
+
+func TestIsPowOfTwoUseLog(t *testing.T) {
+	tests := getTestsForPowerOfTwo()
+	for _, tv := range tests {
+		t.Run(tv.name, func(t *testing.T) {
+			result := IsPowOfTwoUseLog(float64(tv.a))
+			t.Log(tv.a, " ", result)
+			if result != tv.missing {
+				t.Errorf("Wrong result! Expected:%v, returned:%v ", tv.missing, result)
+			}
+		})
+	}
+}
+
+func BenchmarkIsPowerOfTwoUseLog(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		IsPowOfTwoUseLog(1024)
+	}
+}