fixes bug 235272 "RFind is broken [was: Thunderbird treats two-letter folder msf files as folders themselves]" r=jst sr=bienvenu

xpcom/string/src/nsStringObsolete.cpp

@@ -957,46 +957,48 @@ Find_ComputeSearchRange( PRUint32 bigLen, PRUint32 littleLen, PRInt32& offset, P
   /**
    * this method changes the meaning of |offset| and |count|:
    *
+   * upon entry,
+   *   |offset| specifies the end point from which to search backwards
+   *   |count| specifies the number of iterations from |offset|
+   * 
    * upon return,
    *   |offset| specifies start of search range
    *   |count| specifies length of search range
+   *
+   *
+   * EXAMPLE
+   * 
+   *                            + -- littleLen=4 -- +
+   *                            :                   :
+   *   |____|____|____|____|____|____|____|____|____|____|____|____|
+   *                            :                                  :
+   *                         offset=5                           bigLen=12
+   *
+   *   if count = 4, then we expect this function to return offset = 2 and
+   *   count = 7.
+   *
    */ 
 static void
 RFind_ComputeSearchRange( PRUint32 bigLen, PRUint32 littleLen, PRInt32& offset, PRInt32& count )
   {
-    // |count| specifies how many iterations to make from |offset|
-
     if (littleLen > bigLen)
       {
+        offset = 0;
         count = 0;
         return;
       }
 
-    PRInt32 maxOffset = PRInt32(bigLen - littleLen);
     if (offset < 0)
-      {
-        offset = maxOffset;
-      }
-    else if (offset > maxOffset)
-      {
-        count = 0;
-        return;
-      }
+      offset = bigLen - littleLen;
+    if (count < 0)
+      count = offset + 1;
 
-    // always do at least one iteration
-    PRInt32 maxCount = offset + 1;
-    if (count < 0 || count > maxCount)
-      {
-        count = maxCount;
-      }
-    else
-      {
-        count += littleLen;
-        if (count > maxCount)
-          count = maxCount;
-      }
+    PRInt32 start = offset - count + 1;
+    if (start < 0)
+      start = 0;
 
-    offset -= (count - littleLen);
+    count = offset + littleLen - start;
+    offset = start;
   }
 
 //-----------------------------------------------------------------------------

xpcom/tests/TestStrings.cpp

@@ -113,15 +113,41 @@ PRBool test_find()
 PRBool test_rfind()
   {
     const char text[] = "<!DOCTYPE blah blah blah>";
+    const char term[] = "bLaH";
     nsCString src(text);
-    PRInt32 i = src.RFind("bLaH", PR_TRUE, 3, -1); 
-    if (i == -1)
-      return PR_TRUE;
+    PRInt32 i;
 
-    printf("i=%d\n", i);
+    i = src.RFind(term, PR_TRUE, 3, -1); 
+    if (i != kNotFound)
+      {
+        printf("unexpected result searching from offset=3, i=%d\n", i);
         return PR_FALSE;
       }
 
+    i = src.RFind(term, PR_TRUE, -1, -1);
+    if (i != 20)
+      {
+        printf("unexpected result searching from offset=-1, i=%d\n", i);
+        return PR_FALSE;
+      }
+
+    i = src.RFind(term, PR_TRUE, 13, -1);
+    if (i != 10)
+      {
+        printf("unexpected result searching from offset=13, i=%d\n", i);
+        return PR_FALSE;
+      }
+
+    i = src.RFind(term, PR_TRUE, 22, 3);
+    if (i != 20)
+      {
+        printf("unexpected result searching from offset=22, i=%d\n", i);
+        return PR_FALSE;
+      }
+
+    return PR_TRUE;
+  }
+
 PRBool test_rfind_2()
   {
     const char text[] = "<!DOCTYPE blah blah blah>";
@@ -146,6 +172,19 @@ PRBool test_rfind_3()
     return PR_FALSE;
   }
 
+PRBool test_rfind_4()
+  {
+    nsCString value("a.msf");
+    PRInt32 i = value.RFind(".msf");
+    if (i != 1)
+      {
+        printf("i=%d\n", i);
+        return PR_FALSE;
+      }
+
+    return PR_TRUE;
+  }
+
 PRBool test_distance()
   {
     const char text[] = "abc-xyz";
@@ -444,6 +483,7 @@ tests[] =
     { "test_rfind", test_rfind },
     { "test_rfind_2", test_rfind_2 },
     { "test_rfind_3", test_rfind_3 },
+    { "test_rfind_4", test_rfind_4 },
     { "test_distance", test_distance },
     { "test_length", test_length },
     { "test_trim", test_trim },