BAEL-9186 Convert BCD to Decimal (#18876)

Co-authored-by: Nikhil Bhargava <[email protected]>

Author: nikhil1980

algorithms-modules/algorithms-numeric/src/main/java/com/baeldung/algorithms/bcdtodecimal/BCDtoDecimalConverter.java

@@ -0,0 +1,48 @@
+package com.baeldung.algorithms.bcdtodecimal;
+
+public class BCDtoDecimalConverter {
+    /**
+     * Converts a single packed BCD byte to an integer.
+     * Each byte represents two decimal digits.
+     *
+     * @param bcdByte The BCD byte to convert.
+     * @return The decimal integer value.
+     * @throws IllegalArgumentException if any nibble contains a non-BCD value (>9).
+     */
+    public static int convertPackedByte(byte bcdByte) {
+        int resultDecimal;
+        int upperNibble = (bcdByte >> 4) & 0x0F;
+        int lowerNibble = bcdByte & 0x0F;
+        if (upperNibble > 9 || lowerNibble > 9) {
+            throw new IllegalArgumentException(
+                String.format("Invalid BCD format: byte 0x%02X contains non-decimal digit.", bcdByte)
+            );
+        }
+        resultDecimal = upperNibble * 10 + lowerNibble;
+        return resultDecimal;
+    }
+
+    /**
+     * Converts a BCD byte array to a long decimal value.
+     * Each byte in the array iis mapped to a packed BCD byte,
+     * representing two BCD nibbles.
+     *
+     * @param bcdArray The array of BCD bytes.
+     * @return The combined long decimal value.
+     * @throws IllegalArgumentException if any nibble contains a non-BCD value (>9).
+     */
+    public static long convertPackedByteArray(byte[] bcdArray) {
+        long resultDecimal = 0;
+        for (byte bcd : bcdArray) {
+            int upperNibble = (bcd >> 4) & 0x0F;
+            int lowerNibble = bcd & 0x0F;
+
+            if (upperNibble > 9 || lowerNibble > 9) {
+                throw new IllegalArgumentException("Invalid BCD format: nibble contains non-decimal digit.");
+            }
+
+            resultDecimal = resultDecimal * 100 + (upperNibble * 10 + lowerNibble);
+        }
+        return resultDecimal;
+    }
+}

algorithms-modules/algorithms-numeric/src/test/java/com/baeldung/algorithms/bcdtodecimal/BCDtoDecimalConverterTest.java

@@ -0,0 +1,95 @@
+package com.baeldung.algorithms.bcdtodecimal;
+
+import org.junit.jupiter.api.Test;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+public class BCDtoDecimalConverterTest {
+
+    // 1. Tests for convertPackedByte(byte bcdByte)
+
+    @Test
+    void testConvertPackedByteValidValues() {
+        // Test 05 (0x05) ->
+        assertEquals(5, BCDtoDecimalConverter.convertPackedByte((byte) 0x05));
+
+        // Test 22 (0x22) -> 22
+        assertEquals(22, BCDtoDecimalConverter.convertPackedByte((byte) 0x22));
+
+        // Test 97 (0x097) -> 97
+        assertEquals(97, BCDtoDecimalConverter.convertPackedByte((byte) 0x097));
+    }
+
+    @Test
+    void testConvertPackedByteInvalidUpperNibbleThrowsException() {
+        // Test Upper nibble is A (1010), Lower nibble is 1 (0001) -> 0xA1
+        byte invalidByte = (byte) 0xA1;
+        assertThrows(IllegalArgumentException.class, () -> BCDtoDecimalConverter.convertPackedByte(invalidByte),
+            "Received non-BCD upper nibble (A). Provide valid BCD nibbles (0-9).");
+    }
+
+    @Test
+    void testConvertPackedByteBothInvalidThrowsException() {
+        // test Upper nibble is B, Lower nibble is E -> 0xBE
+        byte invalidByte = (byte) 0xBE;
+        assertThrows(IllegalArgumentException.class,
+            () -> BCDtoDecimalConverter.convertPackedByte(invalidByte),
+            "Received both nibbles as non-BCD. Provide valid BCD nibbles (0-9)."
+        );
+    }
+
+    // -------------------------------------------------------------------------
+
+    // 2. Tests for convertPackedByteArray(byte[] bcdArray)
+
+    @Test
+    void testConvertPackedByteArrayValidValues() {
+        // Test 0 -> [0x00]
+        assertEquals(0L, BCDtoDecimalConverter.convertPackedByteArray(new byte[]{(byte) 0x00}));
+
+        // Test 99 -> [0x99]
+        assertEquals(99L, BCDtoDecimalConverter.convertPackedByteArray(new byte[]{(byte) 0x99}));
+
+        // Test 1234 -> [0x12, 0x34]
+        byte[] bcd1234 = {(byte) 0x12, (byte) 0x34};
+        assertEquals(1234L, BCDtoDecimalConverter.convertPackedByteArray(bcd1234));
+
+        // Test 12345678 -> [0x12, 0x34, 0x56, 0x78]
+        byte[] bcdLarge = {(byte) 0x12, (byte) 0x34, (byte) 0x56, (byte) 0x78};
+        assertEquals(12345678L, BCDtoDecimalConverter.convertPackedByteArray(bcdLarge));
+    }
+
+    @Test
+    void testConvertPackedByteArrayEmptyArray() {
+        // Test empty array -> 0
+        assertEquals(0L, BCDtoDecimalConverter.convertPackedByteArray(new byte[]{}));
+    }
+
+    @Test
+    void testConvertPackedByteArrayMaximumSafeLong() {
+        // Test a large number that fits within a long (18 digits)
+        // 999,999,999,999,999,999 (18 nines)
+        byte[] bcdMax = {(byte) 0x99, (byte) 0x99, (byte) 0x99, (byte) 0x99, (byte) 0x99, (byte) 0x99, (byte) 0x99, (byte) 0x99, (byte) 0x99};
+        assertEquals(999999999999999999L, BCDtoDecimalConverter.convertPackedByteArray(bcdMax));
+    }
+
+    @Test
+    void testConvertPackedByteArrayInvalidNibbleThrowsException() {
+        // Contains 0x1A (A is an invalid BCD digit)
+        byte[] bcdInvalid = {(byte) 0x12, (byte) 0x1A, (byte) 0x34};
+        assertThrows(IllegalArgumentException.class,
+            () -> BCDtoDecimalConverter.convertPackedByteArray(bcdInvalid),
+            "Received array containing an invalid BCD byte. Provide valid BCD nibbles (0-9)."
+        );
+    }
+
+    @Test
+    void testConvertPackedByteArray_InvalidFirstByteThrowsException() {
+        // Invalid BCD byte at the start
+        byte[] bcdInvalid = {(byte) 0xF0, (byte) 0x12};
+        assertThrows(IllegalArgumentException.class,
+            () -> BCDtoDecimalConverter.convertPackedByteArray(bcdInvalid),
+            "Received first byte as an invalid BCD byte. Provide valid BCD nibbles (0-9)."
+        );
+    }
+}