Merge pull request #762 from MaxFreedomPollard/fix-numdigits-zero-and-one

Fix Util.numDigits returning 0 for 0 and 1, and 18 for 1E18

Author: leerho

src/main/java/org/apache/datasketches/common/Util.java

@@ -798,13 +798,21 @@ public static int bitAt(final long number, final int bitPos) {
   /** Decimal Digits ***************************/
 
   /**
-   * Computes the number of decimal digits of the number n
-   * @param n the given number
-   * @return the number of decimal digits of the number n
-   */
-  public static int numDigits(long n) {
-    if ((n % 10) == 0) { n++; }
-    return (int) ceil(log(n) / log(10));
+   * Computes the minimum number of characters required to print the number n as a decimal.
+   * Negative numbers add one for the minus sign character.
+   * No other non-digit characters are assumed.
+   * @param n the given number, which may be negative.
+   * @return the number of characters required to print the number n as a decimal
+   */
+  public static int numDigits(final long n) {
+    if (n == 0) { return 1; }    //handles the zero special case
+    int count = (n < 0) ? 1 : 0; //handles the minus sign
+    long v = n;
+    while (v != 0) {
+      v /= 10;
+      count++;
+    }
+    return count;
   }
 
   /** Generic relational tests *****************/

src/test/java/org/apache/datasketches/common/UtilTest.java

@@ -46,6 +46,7 @@
 import static org.apache.datasketches.common.Util.longToBytes;
 import static org.apache.datasketches.common.Util.milliSecToString;
 import static org.apache.datasketches.common.Util.nanoSecToString;
+import static org.apache.datasketches.common.Util.numDigits;
 import static org.apache.datasketches.common.Util.numberOfLeadingOnes;
 import static org.apache.datasketches.common.Util.numberOfTrailingOnes;
 import static org.apache.datasketches.common.Util.powerSeriesNextDouble;
@@ -241,6 +242,25 @@ public void checkCharacterPad() {
     assertEquals(out,"zzzzzzzzzzzzPad 30, prepend z:");
   }
 
+  /**
+   * Check all the transition points where the number of decimal characters change.
+   */
+  @Test
+  public void checkNumDigits() {
+    for (long n = 1; n > 0; n *= 10) { //n goes negative on rollover, which halts the loop
+      checkN(n);
+      checkN(n - 1);
+      checkN(-n);
+      checkN(-n + 1);
+    }
+    checkN(Long.MAX_VALUE);
+    checkN(Long.MIN_VALUE);
+  }
+
+  private static void checkN(final long n) {
+    assertEquals(numDigits(n), String.valueOf(n).length());
+  }
+
   @Test
   public void checkProbabilityFn1() {
     checkProbability(.5, "Good");