#include "shim.h"


/* Expand the heap in-place if brk can be used, or otherwise via mmap,
 * using an exponential lower bound on growth by mmap to make
 * fragmentation asymptotically irrelevant. The size argument is both
 * an input and an output, since the caller needs to know the size
 * allocated, which will be larger than requested due to page alignment
 * and mmap minimum size rules. The caller is responsible for locking
 * to prevent concurrent calls. */

void *__expand_heap(size_t *pn)
{
	static unsigned mmap_step;
	size_t n = *pn;

	if (n > SIZE_MAX/2 - PAGE_SIZE) {
		errno = ENOMEM;
		return 0;
	}
	n += -n & PAGE_SIZE-1;

	size_t min = (size_t)PAGE_SIZE << mmap_step/2;
	if (n < min) n = min;
	void *area = mmap(0, n, PROT_READ|PROT_WRITE,
		MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
	if (area == MAP_FAILED) return 0;
	*pn = n;
	mmap_step++;
	return area;
}