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Fix Util.numDigits returning 0 for 0 and 1, and 18 for 1E18 #762

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Merged
leerho merged 4 commits into from
Sep 16, 2026
+35 −7
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Fix Util.numDigits returning 0 for 0 and 1, and 18 for 1E18 #762

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bda4c33
Fix Util.numDigits returning 0 for 0 and 1, and 18 for 1E18
MaxFreedomPollard Sep 7, 2026
6040f84
Make numDigits count characters including the minus sign
MaxFreedomPollard Sep 9, 2026
6498a90
Drop the always true loop guard in checkNumDigits
MaxFreedomPollard Sep 10, 2026
accfafb
Check only the decimal-character transition points in checkNumDigits
Sep 14, 2026
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22 changes: 15 additions & 7 deletions src/main/java/org/apache/datasketches/common/Util.java
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Original file line number Diff line number Diff line change
Expand Up @@ -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 *****************/
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20 changes: 20 additions & 0 deletions src/test/java/org/apache/datasketches/common/UtilTest.java
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Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand Down Expand Up @@ -241,6 +242,25 @@
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
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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");
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