-/* Ensure there are at least RESERVE free slots in VEC, if RESERVE !=
- ~0u. If RESERVE == ~0u increase the current allocation
- exponentially. VEC can be NULL, to create a new vector. */
+/* Calculate the new ALLOC value, making sure that abs(RESERVE) slots
+ are free. If RESERVE < 0 grow exactly, otherwise grow
+ exponentially. */
+
+static inline unsigned
+calculate_allocation (const struct vec_prefix *pfx, int reserve)
+{
+ unsigned alloc = 0;
+ unsigned num = 0;
+
+ if (pfx)
+ {
+ alloc = pfx->alloc;
+ num = pfx->num;
+ }
+ else if (!reserve)
+ /* If there's no prefix, and we've not requested anything, then we
+ will create a NULL vector. */
+ return 0;
+
+ /* We must have run out of room. */
+ gcc_assert (alloc - num < (unsigned)(reserve < 0 ? -reserve : reserve));
+
+ if (reserve < 0)
+ /* Exact size. */
+ alloc = num + -reserve;
+ else
+ {
+ /* Exponential growth. */
+ if (!alloc)
+ alloc = 4;
+ else if (alloc < 16)
+ /* Double when small. */
+ alloc = alloc * 2;
+ else
+ /* Grow slower when large. */
+ alloc = (alloc * 3 / 2);
+
+ /* If this is still too small, set it to the right size. */
+ if (alloc < num + reserve)
+ alloc = num + reserve;
+ }
+ return alloc;
+}
+
+/* Ensure there are at least abs(RESERVE) free slots in VEC. If
+ RESERVE < 0 grow exactly, else grow exponentially. As a special
+ case, if VEC is NULL, and RESERVE is 0, no vector will be created. */