musl/src/malloc/lite_malloc.c

#include <stdlib.h>
#include <stdint.h>
#include <limits.h>
#include <errno.h>
#include "libc.h"

#define ALIGN 16

void *__expand_heap(size_t *);

void *__simple_malloc(size_t n)
{
	static char *cur, *end;
	static volatile int lock[2];
	size_t align=1, pad;
	void *p;

	if (!n) n++;
	while (align<n && align<ALIGN)
		align += align;

	LOCK(lock);

	pad = -(uintptr_t)cur & align-1;

	if (n <= SIZE_MAX/2 + ALIGN) n += pad;

	if (n > end-cur) {
		size_t m = n;
		char *new = __expand_heap(&m);
		if (!new) {
			UNLOCK(lock);
			return 0;
		}
		if (new != end) {
			cur = new;
			n -= pad;
			pad = 0;
		}
		end = new + m;
	}

	p = cur + pad;
	cur += n;
	UNLOCK(lock);
	return p;
}

weak_alias(__simple_malloc, malloc);
weak_alias(__simple_malloc, malloc0);