diff --git a/src/main/java/com/thealgorithms/bitmanipulation/BitRotate.java b/src/main/java/com/thealgorithms/bitmanipulation/BitRotate.java new file mode 100644 index 000000000..226e09e78 --- /dev/null +++ b/src/main/java/com/thealgorithms/bitmanipulation/BitRotate.java @@ -0,0 +1,83 @@ +package com.thealgorithms.bitmanipulation; + +/** + * Utility class for performing circular bit rotations on 32-bit integers. + * Bit rotation is a circular shift operation where bits shifted out on one end + * are reinserted on the opposite end. + * + *

This class provides methods for both left and right circular rotations, + * supporting only 32-bit integer operations with proper shift normalization + * and error handling.

+ * + * @see Bit Rotation + */ +public final class BitRotate { + + /** + * Private constructor to prevent instantiation. + * This is a utility class with only static methods. + */ + private BitRotate() { + throw new UnsupportedOperationException("This is a utility class and cannot be instantiated"); + } + + /** + * Performs a circular left rotation (left shift) on a 32-bit integer. + * Bits shifted out from the left side are inserted on the right side. + * + * @param value the 32-bit integer value to rotate + * @param shift the number of positions to rotate left (must be non-negative) + * @return the result of left rotating the value by the specified shift amount + * @throws IllegalArgumentException if shift is negative + * + * @example + * // Binary: 10000000 00000000 00000000 00000001 + * rotateLeft(0x80000001, 1) + * // Returns: 3 (binary: 00000000 00000000 00000000 00000011) + */ + public static int rotateLeft(int value, int shift) { + if (shift < 0) { + throw new IllegalArgumentException("Shift amount cannot be negative: " + shift); + } + + // Normalize shift to the range [0, 31] using modulo 32 + shift = shift % 32; + + if (shift == 0) { + return value; + } + + // Left rotation: (value << shift) | (value >>> (32 - shift)) + return (value << shift) | (value >>> (32 - shift)); + } + + /** + * Performs a circular right rotation (right shift) on a 32-bit integer. + * Bits shifted out from the right side are inserted on the left side. + * + * @param value the 32-bit integer value to rotate + * @param shift the number of positions to rotate right (must be non-negative) + * @return the result of right rotating the value by the specified shift amount + * @throws IllegalArgumentException if shift is negative + * + * @example + * // Binary: 00000000 00000000 00000000 00000011 + * rotateRight(3, 1) + * // Returns: -2147483647 (binary: 10000000 00000000 00000000 00000001) + */ + public static int rotateRight(int value, int shift) { + if (shift < 0) { + throw new IllegalArgumentException("Shift amount cannot be negative: " + shift); + } + + // Normalize shift to the range [0, 31] using modulo 32 + shift = shift % 32; + + if (shift == 0) { + return value; + } + + // Right rotation: (value >>> shift) | (value << (32 - shift)) + return (value >>> shift) | (value << (32 - shift)); + } +} diff --git a/src/test/java/com/thealgorithms/bitmanipulation/BitRotateTest.java b/src/test/java/com/thealgorithms/bitmanipulation/BitRotateTest.java new file mode 100644 index 000000000..0595ae5a7 --- /dev/null +++ b/src/test/java/com/thealgorithms/bitmanipulation/BitRotateTest.java @@ -0,0 +1,205 @@ +package com.thealgorithms.bitmanipulation; + +import static org.junit.jupiter.api.Assertions.assertDoesNotThrow; +import static org.junit.jupiter.api.Assertions.assertEquals; +import static org.junit.jupiter.api.Assertions.assertThrows; +import static org.junit.jupiter.api.Assertions.assertTrue; + +import org.junit.jupiter.api.Test; + +/** + * Unit tests for BitRotate class covering typical, boundary, and edge cases. + * Tests verify correct behavior for 32-bit circular bit rotations. + * + * @author Yajunesh + */ +public class BitRotateTest { + + // ===== rotateLeft Tests ===== + + @Test + public void testRotateLeftBasic() { + // Basic left rotation + assertEquals(0b00000000_00000000_00000000_00000010, BitRotate.rotateLeft(1, 1)); + assertEquals(0b00000000_00000000_00000000_00000100, BitRotate.rotateLeft(1, 2)); + assertEquals(0b00000000_00000000_00000000_00001000, BitRotate.rotateLeft(1, 3)); + } + + @Test + public void testRotateLeftWithCarry() { + // Test bits carrying from left to right + // Binary: 10000000_00000000_00000000_00000001 + int value = 0x80000001; + // After left rotate by 1: 00000000_00000000_00000000_00000011 + assertEquals(3, BitRotate.rotateLeft(value, 1)); + + // Binary: 11000000_00000000_00000000_00000000 + value = 0xC0000000; + // After left rotate by 1: 10000000_00000000_00000000_00000001 + assertEquals(0x80000001, BitRotate.rotateLeft(value, 1)); + } + + @Test + public void testRotateLeftShift32() { + // Shift of 32 should be same as shift of 0 (modulo behavior) + int value = 0x12345678; + assertEquals(value, BitRotate.rotateLeft(value, 32)); + assertEquals(value, BitRotate.rotateLeft(value, 64)); + assertEquals(value, BitRotate.rotateLeft(value, 96)); + } + + @Test + public void testRotateLeftShiftNormalization() { + // Test that shifts > 32 are properly normalized + int value = 1; + assertEquals(BitRotate.rotateLeft(value, 1), BitRotate.rotateLeft(value, 33)); + assertEquals(BitRotate.rotateLeft(value, 5), BitRotate.rotateLeft(value, 37)); + } + + @Test + public void testRotateLeftZeroShift() { + // Zero shift should return original value + int value = 0xABCD1234; + assertEquals(value, BitRotate.rotateLeft(value, 0)); + } + + // ===== rotateRight Tests ===== + + @Test + public void testRotateRightBasic() { + // Basic right rotation + assertEquals(0b10000000_00000000_00000000_00000000, BitRotate.rotateRight(1, 1)); + assertEquals(0b01000000_00000000_00000000_00000000, BitRotate.rotateRight(1, 2)); + assertEquals(0b00100000_00000000_00000000_00000000, BitRotate.rotateRight(1, 3)); + } + + @Test + public void testRotateRightWithCarry() { + // Test bits carrying from right to left + // Binary: 00000000_00000000_00000000_00000011 + int value = 3; + // After right rotate by 1: 10000000_00000000_00000000_00000001 + assertEquals(0x80000001, BitRotate.rotateRight(value, 1)); + + // Binary: 00000000_00000000_00000000_00000001 + value = 1; + // After right rotate by 1: 10000000_00000000_00000000_00000000 + assertEquals(0x80000000, BitRotate.rotateRight(value, 1)); + } + + @Test + public void testRotateRightShift32() { + // Shift of 32 should be same as shift of 0 (modulo behavior) + int value = 0x9ABCDEF0; + assertEquals(value, BitRotate.rotateRight(value, 32)); + assertEquals(value, BitRotate.rotateRight(value, 64)); + assertEquals(value, BitRotate.rotateRight(value, 96)); + } + + @Test + public void testRotateRightShiftNormalization() { + // Test that shifts > 32 are properly normalized + int value = 1; + assertEquals(BitRotate.rotateRight(value, 1), BitRotate.rotateRight(value, 33)); + assertEquals(BitRotate.rotateRight(value, 7), BitRotate.rotateRight(value, 39)); + } + + @Test + public void testRotateRightZeroShift() { + // Zero shift should return original value + int value = 0xDEADBEEF; + assertEquals(value, BitRotate.rotateRight(value, 0)); + } + + // ===== Edge Case Tests ===== + + @Test + public void testRotateLeftMaxValue() { + // Test with maximum integer value + int value = Integer.MAX_VALUE; // 0x7FFFFFFF + int rotated = BitRotate.rotateLeft(value, 1); + // MAX_VALUE << 1 should become 0xFFFFFFFE, but with rotation it becomes different + assertEquals(0xFFFFFFFE, rotated); + } + + @Test + public void testRotateRightMinValue() { + // Test with minimum integer value (treated as unsigned) + int value = Integer.MIN_VALUE; // 0x80000000 + int rotated = BitRotate.rotateRight(value, 1); + // MIN_VALUE >>> 1 should become 0x40000000, but with rotation from left + assertEquals(0x40000000, rotated); + } + + @Test + public void testRotateAllOnes() { + // Test with all bits set + int value = 0xFFFFFFFF; // All ones + assertEquals(value, BitRotate.rotateLeft(value, 13)); + assertEquals(value, BitRotate.rotateRight(value, 27)); + } + + @Test + public void testRotateAllZeros() { + // Test with all bits zero + int value = 0x00000000; + assertEquals(value, BitRotate.rotateLeft(value, 15)); + assertEquals(value, BitRotate.rotateRight(value, 19)); + } + + // ===== Exception Tests ===== + + @Test + public void testRotateLeftNegativeShift() { + // Negative shifts should throw IllegalArgumentException + Exception exception = assertThrows(IllegalArgumentException.class, () -> BitRotate.rotateLeft(42, -1)); + assertTrue(exception.getMessage().contains("negative")); + } + + @Test + public void testRotateRightNegativeShift() { + // Negative shifts should throw IllegalArgumentException + Exception exception = assertThrows(IllegalArgumentException.class, () -> BitRotate.rotateRight(42, -5)); + assertTrue(exception.getMessage().contains("negative")); + } + + // ===== Complementary Operations Test ===== + + @Test + public void testRotateLeftRightComposition() { + // Rotating left then right by same amount should return original value + int original = 0x12345678; + int shift = 7; + + int leftRotated = BitRotate.rotateLeft(original, shift); + int restored = BitRotate.rotateRight(leftRotated, shift); + + assertEquals(original, restored); + } + + @Test + public void testRotateRightLeftComposition() { + // Rotating right then left by same amount should return original value + int original = 0x9ABCDEF0; + int shift = 13; + + int rightRotated = BitRotate.rotateRight(original, shift); + int restored = BitRotate.rotateLeft(rightRotated, shift); + + assertEquals(original, restored); + } + + @Test + public void testRotateLeft31IsSameAsRotateRight1() { + // Rotating left by 31 should be same as rotating right by 1 + int value = 0x55555555; + assertEquals(BitRotate.rotateLeft(value, 31), BitRotate.rotateRight(value, 1)); + } + + @Test + public void testTraversals() { + // Test that methods don't throw exceptions + assertDoesNotThrow(() -> BitRotate.rotateLeft(1, 1)); + assertDoesNotThrow(() -> BitRotate.rotateRight(1, 1)); + } +}