This looks like an oversight from "quickly testing a potential fix" and
then forgetting to make a production-ready when it works.
https://bugzilla.gnome.org/show_bug.cgi?id=755691
for (i = start_word; i <= end_word; i++)
mask->data[i] ^= ALL_BITS;
mask->data[start_word] ^= (((VALUE_TYPE) 1) << start_bit) - 1;
- if (end_bit != 63)
+ if (end_bit != VALUE_SIZE_BITS - 1)
mask->data[end_word] ^= ALL_BITS << (end_bit + 1);
return gtk_allocated_bitmask_shrink (mask);