Refactor BCD Conversion docs and add more tests (#5762)

src/main/java/com/thealgorithms/bitmanipulation/BcdConversion.java

@@ -1,56 +1,80 @@
 package com.thealgorithms.bitmanipulation;
 
 /**
- * This class provides methods to convert between BCD (Binary-Coded Decimal) and binary.
+ * This class provides methods to convert between BCD (Binary-Coded Decimal) and decimal numbers.
  *
- * Binary-Coded Decimal (BCD) is a class of binary encodings of decimal numbers where each decimal digit is represented by a fixed number of binary digits, usually four or eight.
+ * BCD is a class of binary encodings of decimal numbers where each decimal digit is represented by a fixed number of binary digits, usually four or eight.
  *
  * For more information, refer to the
  * <a href="https://en.wikipedia.org/wiki/Binary-coded_decimal">Binary-Coded Decimal</a> Wikipedia page.
  *
  * <b>Example usage:</b>
  * <pre>
- * int binary = BcdConversion.bcdToBinary(0x1234);
- * System.out.println("BCD 0x1234 to binary: " + binary); // Output: 1234
+ * int decimal = BcdConversion.bcdToDecimal(0x1234);
+ * System.out.println("BCD 0x1234 to decimal: " + decimal); // Output: 1234
  *
- * int bcd = BcdConversion.binaryToBcd(1234);
- * System.out.println("Binary 1234 to BCD: " + Integer.toHexString(bcd)); // Output: 0x1234
+ * int bcd = BcdConversion.decimalToBcd(1234);
+ * System.out.println("Decimal 1234 to BCD: " + Integer.toHexString(bcd)); // Output: 0x1234
  * </pre>
  */
 public final class BcdConversion {
     private BcdConversion() {
     }
+
     /**
-     * Converts a BCD (Binary-Coded Decimal) number to binary.
+     * Converts a BCD (Binary-Coded Decimal) number to a decimal number.
+     * <p>Steps:
+     * <p>1. Validate the BCD number to ensure all digits are between 0 and 9.
+     * <p>2. Extract the last 4 bits (one BCD digit) from the BCD number.
+     * <p>3. Multiply the extracted digit by the corresponding power of 10 and add it to the decimal number.
+     * <p>4. Shift the BCD number right by 4 bits to process the next BCD digit.
+     * <p>5. Repeat steps 1-4 until the BCD number is zero.
      *
      * @param bcd The BCD number.
-     * @return The corresponding binary number.
+     * @return The corresponding decimal number.
+     * @throws IllegalArgumentException if the BCD number contains invalid digits.
      */
-    public static int bcdToBinary(int bcd) {
-        int binary = 0;
+    public static int bcdToDecimal(int bcd) {
+        int decimal = 0;
         int multiplier = 1;
+
+        // Validate BCD digits
         while (bcd > 0) {
-            int digit = bcd & 0xF; // Extract the last 4 bits (one BCD digit)
-            binary += digit * multiplier;
+            int digit = bcd & 0xF;
+            if (digit > 9) {
+                throw new IllegalArgumentException("Invalid BCD digit: " + digit);
+            }
+            decimal += digit * multiplier;
             multiplier *= 10;
-            bcd >>= 4; // Shift right by 4 bits to process the next BCD digit
+            bcd >>= 4;
         }
-        return binary;
+        return decimal;
     }
 
     /**
-     * Converts a binary number to BCD (Binary-Coded Decimal).
+     * Converts a decimal number to BCD (Binary-Coded Decimal).
+     * <p>Steps:
+     * <p>1. Check if the decimal number is within the valid range for BCD (0 to 9999).
+     * <p>2. Extract the last decimal digit from the decimal number.
+     * <p>3. Shift the digit to the correct BCD position and add it to the BCD number.
+     * <p>4. Remove the last decimal digit from the decimal number.
+     * <p>5. Repeat steps 2-4 until the decimal number is zero.
      *
-     * @param binary The binary number.
+     * @param decimal The decimal number.
      * @return The corresponding BCD number.
+     * @throws IllegalArgumentException if the decimal number is greater than 9999.
      */
-    public static int binaryToBcd(int binary) {
+    public static int decimalToBcd(int decimal) {
+        if (decimal < 0 || decimal > 9999) {
+            throw new IllegalArgumentException("Value out of bounds for BCD representation: " + decimal);
+        }
+
         int bcd = 0;
         int shift = 0;
-        while (binary > 0) {
-            int digit = binary % 10; // Extract the last decimal digit
-            bcd |= (digit << (shift * 4)); // Shift the digit to the correct BCD position
-            binary /= 10; // Remove the last decimal digit
+        while (decimal > 0) {
+            int digit = decimal % 10;
+            bcd |= (digit << (shift * 4));
+            decimal /= 10;
             shift++;
         }
         return bcd;