feat: Add BitRotate utility for circular bit rotations

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.
+ *
+ * <p>This class provides methods for both left and right circular rotations,
+ * supporting only 32-bit integer operations with proper shift normalization
+ * and error handling.</p>
+ *
+ * @see <a href="https://en.wikipedia.org/wiki/Bit_rotation">Bit Rotation</a>
+ */
+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));
+    }
+}

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));
+    }
+}