bug 16688, r=ftang@netscape.com, sr=blizzard@mozilla.org

support macro for:
  if fixed length conversion buffer too short malloc

intl/uconv/public/nsIUnicodeEncoder.h

@@ -71,6 +71,41 @@ public:
   NS_IMETHOD Convert(PRUnichar aChar, char * aDest, PRInt32 * aDestLength) = 0;
 };
 
+//
+// Malloc an Encoder (unicode -> charset) buffer if the
+// result won't fit in the static buffer
+//
+//    p = the buffer pointer   (char*)
+//    e = encoder              (nsIUnicodeEncoder*)
+//    s = string               (PRUnichar*)
+//    l = string length        (PRInt32)
+//   sb = static buffer        (char[])
+//  sbl = static buffer length (PRUint32)
+//   al = actual buffer length (PRInt32)
+//
+#define ENCODER_BUFFER_ALLOC_IF_NEEDED(p,e,s,l,sb,sbl,al) \
+  PR_BEGIN_MACRO                                          \
+    nsresult rv = (e)->GetMaxLength((s), (l), &(al));     \
+    if (NS_SUCCEEDED(rv)                                  \
+        && ((al) > (PRInt32)(sbl))                        \
+        && (nsnull!=((p)=(char*)nsMemory::Alloc((al)+1))) \
+        ) {                                               \
+    }                                                     \
+    else {                                                \
+      (p) = (char*)(sb);                                  \
+      (al) = (sbl);                                       \
+    }                                                     \
+  PR_END_MACRO 
+
+//
+// Free the Encoder buffer if it was allocated
+//
+#define ENCODER_BUFFER_FREE_IF_NEEDED(p,sb) \
+  PR_BEGIN_MACRO                            \
+    if ((p) != (char*)(sb))                 \
+      nsMemory::Free(p);                    \
+  PR_END_MACRO 
+
 /**
  * Interface for a Converter from Unicode into a Charset.
  *