ccutil/ambigs: Optimize tesseract::UnicharIdArrayUtils::compare

The compare method is called very often, so even small improvements
are important.

The new code avoids one comparison in each loop iteration.
This results in smaller code (60 bytes for x86_64, gcc).

Signed-off-by: Stefan Weil <sw@weilnetz.de>

ccutil/ambigs.h

@@ -59,17 +59,19 @@ class UnicharIdArrayUtils {
   // less than length of array2, if any array1[i] is less than array2[i].
   // Returns 0 if the arrays are equal, 1 otherwise.
   // The function assumes that the arrays are terminated by INVALID_UNICHAR_ID.
-  static inline int compare(const UNICHAR_ID array1[],
-                            const UNICHAR_ID array2[]) {
-    const UNICHAR_ID *ptr1 = array1;
-    const UNICHAR_ID *ptr2 = array2;
-    while (*ptr1 != INVALID_UNICHAR_ID && *ptr2 != INVALID_UNICHAR_ID) {
-      if (*ptr1 != *ptr2) return *ptr1 < *ptr2 ? -1 : 1;
-      ++ptr1;
-      ++ptr2;
+  static inline int compare(const UNICHAR_ID *ptr1,
+                            const UNICHAR_ID *ptr2) {
+    for (;;) {
+      const UNICHAR_ID val1 = *ptr1++;
+      const UNICHAR_ID val2 = *ptr2++;
+      if (val1 != val2) {
+        if (val1 == INVALID_UNICHAR_ID) return -1;
+        if (val2 == INVALID_UNICHAR_ID) return 1;
+        if (val1 < val2) return -1;
+        return 1;
+      }
+      if (val1 == INVALID_UNICHAR_ID) return 0;
     }
-    if (*ptr1 == INVALID_UNICHAR_ID && *ptr2 == INVALID_UNICHAR_ID) return 0;
-    return *ptr1 == INVALID_UNICHAR_ID ? -1 : 1;
   }
 
   // Look uid in the vector of uids.  If found, the index of the matched