[skippy-iter] Fix two logic errors
First, a signed underflow.
Second, a wrong condition.
Both were introduced in 42681bdb55a75520d4ac194302fe936d1ce3cb34
diff --git a/src/hb-ot-layout-gsubgpos.hh b/src/hb-ot-layout-gsubgpos.hh
index 6f1c614..5529ccb 100644
--- a/src/hb-ot-layout-gsubgpos.hh
+++ b/src/hb-ot-layout-gsubgpos.hh
@@ -537,10 +537,10 @@
assert (num_items > 0);
/* The alternate condition below is faster at string boundaries,
* but produces subpar "unsafe-to-concat" values. */
- unsigned stop = end - num_items;
+ signed stop = (signed) end - (signed) num_items;
if (c->buffer->flags & HB_BUFFER_FLAG_PRODUCE_UNSAFE_TO_CONCAT)
- stop = end - 1;
- while (idx < stop)
+ stop = (signed) end - 1;
+ while ((signed) idx < stop)
{
idx++;
hb_glyph_info_t &info = c->buffer->info[idx];
@@ -575,7 +575,7 @@
assert (num_items > 0);
/* The alternate condition below is faster at string boundaries,
* but produces subpar "unsafe-to-concat" values. */
- unsigned stop = 1 - num_items;
+ unsigned stop = num_items - 1;
if (c->buffer->flags & HB_BUFFER_FLAG_PRODUCE_UNSAFE_TO_CONCAT)
stop = 1 - 1;
while (idx > stop)
