+FcBool
+FcCharSetMerge (FcCharSet *a, const FcCharSet *b, FcBool *changed)
+{
+ int ai = 0, bi = 0;
+ FcChar16 an, bn;
+
+ if (a->ref == FC_REF_CONSTANT) {
+ if (changed)
+ *changed = FcFalse;
+ return FcFalse;
+ }
+
+ if (changed) {
+ *changed = !FcCharSetIsSubset(b, a);
+ if (!*changed)
+ return FcTrue;
+ }
+
+ while (bi < b->num)
+ {
+ an = ai < a->num ? FcCharSetNumbers(a)[ai] : ~0;
+ bn = FcCharSetNumbers(b)[bi];
+
+ if (an < bn)
+ {
+ ai = FcCharSetFindLeafForward (a, ai + 1, bn);
+ if (ai < 0)
+ ai = -ai - 1;
+ }
+ else
+ {
+ FcCharLeaf *bl = FcCharSetLeaf(b, bi);
+ if (bn < an)
+ {
+ if (!FcCharSetAddLeaf (a, bn << 8, bl))
+ return FcFalse;
+ }
+ else
+ {
+ FcCharLeaf *al = FcCharSetLeaf(a, ai);
+ FcCharSetUnionLeaf (al, al, bl);
+ }
+
+ ai++;
+ bi++;
+ }
+ }
+
+ return FcTrue;
+}
+