Function sz_sa2u

deps/jemalloc/include/jemalloc/internal/sz.h:262–316

* Compute usable size that would result from allocating an object with the * specified size and alignment. */

 * specified size and alignment.
 */
JEMALLOC_ALWAYS_INLINE size_t
sz_sa2u(size_t size, size_t alignment) {
	size_t usize;

	assert(alignment != 0 && ((alignment - 1) & alignment) == 0);

	/* Try for a small size class. */
	if (size <= SC_SMALL_MAXCLASS && alignment < PAGE) {
		/*
		 * Round size up to the nearest multiple of alignment.
		 *
		 * This done, we can take advantage of the fact that for each
		 * small size class, every object is aligned at the smallest
		 * power of two that is non-zero in the base two representation
		 * of the size.  For example:
		 *
		 *   Size |   Base 2 | Minimum alignment
		 *   -----+----------+------------------
		 *     96 |  1100000 |  32
		 *    144 | 10100000 |  32
		 *    192 | 11000000 |  64
		 */
		usize = sz_s2u(ALIGNMENT_CEILING(size, alignment));
		if (usize < SC_LARGE_MINCLASS) {
			return usize;
		}
	}

	/* Large size class.  Beware of overflow. */

	if (unlikely(alignment > SC_LARGE_MAXCLASS)) {
		return 0;
	}

	/* Make sure result is a large size class. */
	if (size <= SC_LARGE_MINCLASS) {
		usize = SC_LARGE_MINCLASS;
	} else {
		usize = sz_s2u(size);
		if (usize < size) {
			/* size_t overflow. */
			return 0;
		}
	}

	/*
	 * Calculate the multi-page mapping that large_palloc() would need in
	 * order to guarantee the alignment.
	 */
	if (usize + sz_large_pad + PAGE_CEILING(alignment) - PAGE < usize) {
		/* size_t overflow. */
		return 0;
	}
	return usize;
}

#endif /* JEMALLOC_INTERNAL_SIZE_H */