Force extended value string linear search (not binary search) in one case:

 Fixed: { -2, -1, 0, 1, 3} (note gap) used a binary search (which would fail);

 Note:  { -2, -1, 0, 1, 2 ,3 } (no gap) allowed; will still do a direct access;

Also: Add a comment to README.developer extended value string section.


git-svn-id: http://anonsvn.wireshark.org/wireshark/trunk@44659 f5534014-38df-0310-8fa8-9805f1628bb7

2 files changed, 26 insertions, 3 deletions

diff --git a/doc/README.developer b/doc/README.developer
index 600cbce8fd..02bc3b73ef 100644
--- a/doc/README.developer
+++ b/doc/README.developer
@@ -1895,9 +1895,9 @@ field would be set to NULL.
 
 -- Extended value strings
 You can also use an extended version of the value_string for faster lookups.
-It requires a value_string as input.
+It requires a value_string array as input.
 If all of a contiguous range of values from min to max are present in the array
-the value will be used as as a direct index into a value_string array.
+in ascending order the value will be used as as a direct index into a value_string array.
 
 If the values in the array are not contiguous (ie: there are "gaps"), but are
 in ascending order a binary search will be used.
@@ -1905,6 +1905,14 @@ in ascending order a binary search will be used.
 Note: "gaps" in a value_string array can be filled with "empty" entries eg:
 {value, "Unknown"} so that direct access to the array is is possible.
 
+Note: the value_string array values are *unsigned*; IOW: -1 is greater than 0.
+      So:
+      { -2, -1,  1,  2 }; wrong:   linear search will be used (note gap)
+      {  1,  2, -2, -1 }; correct: binary search will be used
+
+      As a special case:
+      { -2, -1,  0,  1,  2 }; OK: direct(indexed) access will be used (note no gap)
+
 The init macro (see below) will perform a check on the value string the first
 time it is used to determine which search algorithm fits and fall back to a
 linear search if the value_string does not meet the criteria above.
diff --git a/epan/value_string.c b/epan/value_string.c
index 43453f1f14..f48b3155ff 100644
--- a/epan/value_string.c
+++ b/epan/value_string.c
@@ -285,6 +285,20 @@ _match_strval_ext_init(const guint32 val, const value_string_ext *a_vse)
  * 1 Binary search, the values MUST be in numerical order.
  * 2 The value used as an index(the value string MUST have all values between first and last defined in numerical order)
  */
+
+/* Note: The value_string 'value' is *unsigned*.
+ *
+ *   Special case:
+ *    { -3, -2, -1, 0, 1, 2 }                      will be treated as "ascending ordered" (altho not really such)
+ *                                                  thus allowing as a 'direct' search.
+ *
+ *   Note:
+ *    { -3, -2, 0, 1, 2 } and { -3, -2, -1, 0, 2 } will both be considered as "out-of-order with gaps"
+ *                                                  thus requiring a 'linear' search.
+ *    { 0, 1, 2, -3, -2 } and { 0, 2, -3, -2, -1 } will be considered "ascending ordered with gaps"
+ *                                                  thus allowing a 'binary' search.
+ */
+
   enum { VS_SEARCH = 0, VS_BIN_TREE, VS_INDEX } type = VS_INDEX;
 
   guint32 prev_value;
@@ -303,7 +317,8 @@ _match_strval_ext_init(const guint32 val, const value_string_ext *a_vse)
       type = VS_BIN_TREE;
     }
     /* XXX: Should check for dups ?? */
-    if ((type == VS_BIN_TREE) && (prev_value > vs_p[i].value)) {
+    if ((type == VS_BIN_TREE) &&
+        ((prev_value > vs_p[i].value) || (first_value > vs_p[i].value))) {
       type = VS_SEARCH;
       break;
     }