Bug 6553 - string.CompareOrdinal returns incorrect result
Summary: string.CompareOrdinal returns incorrect result
Alias: None
Product: Class Libraries
Classification: Mono
Component: mscorlib ()
Version: master
Hardware: All All
: --- normal
Target Milestone: Untriaged
Assignee: Bugzilla
Depends on:
Reported: 2012-08-16 07:30 UTC by Steffen Kieß
Modified: 2012-09-04 11:49 UTC (History)
2 users (show)

Is this bug a regression?: ---
Last known good build:

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Description Steffen Kieß 2012-08-16 07:30:09 UTC
string.CompareOrdinal incorrectly returns 0 if both string references point to the same object and the length parameter is small enough to fit into the string for both offsets but the offsets are different.

Steps to reproduce:
cat > StringCompare.cs <<EOF
public class StringCompare {
  public static void Main () {
    string ab1 = "ab";
    string ab2 = "a" + new string ('b', 1); // same string in new object
    System.Console.WriteLine (ab1);
    System.Console.WriteLine (ab2);
    System.Console.WriteLine (string.CompareOrdinal (ab1, 0, ab1, 1, 1)); // should return -1 (because second offset is 1)
    System.Console.WriteLine (string.CompareOrdinal (ab2, 0, ab1, 1, 1)); // correctly returns -1
gmcs StringCompare.cs
mono StringCompare.exe

Actual result:

Expected result:

This is caused by these lines in System.String.CompareOrdinalUnchecked:
                        if (lengthA == lengthB && Object.ReferenceEquals (strA, strB))
                                return 0;
There also should be a check here whether the offsets are equal.

This problem appears both in Mono and in the current git master
Comment 1 Marek Safar 2012-09-04 11:49:43 UTC
Fixed in master