Improve safety of log2 functions

src/buddy.c

@@ -2785,9 +2785,25 @@ t_buddy(size_t free)
 	BUDDYF(fini)(&buddy, BUDDYF(unmap), NULL, NULL, NULL);
 }
 
+static void
+t_log2(size_t min, size_t max)
+{
+	size_t s;
+
+	assert(min > 0);
+	for (s = min; s <= max; s++) {
+		assert(log2down(s) == log2up(s + 1) - 1);
+	}
+	fprintf(stderr, "log2 %zu..%zu OK\n", min, max);
+}
+
 int main(void)
 {
 	t_cramlimit();
+	t_log2(1, (size_t)1 << 30);
+	t_log2(SIZE_MAX - 5, SIZE_MAX - 1);
+	assert(log2up(SIZE_MAX) == sizeof(size_t) * 8);
+	assert(log2down(SIZE_MAX) == sizeof(size_t) * 8 - 1);
 	t_bitf();
 	t_buddy(1 << 15);
 	t_buddy((1 << 15) - 1);

src/buddy_util.h

@@ -50,7 +50,9 @@ rdown_min(size_t size, unsigned minbits)
 static inline unsigned
 log2up(size_t sz)
 {
-
+	if (sz == 1)
+		return (0);
+	assert(sz > 1);
 	sz--;
 	sz = bitsof(sz);
 	assert(sz > 0);
@@ -58,11 +60,13 @@ log2up(size_t sz)
 	return ((unsigned) sz);
 }
 
+// #define log2down(x) (log2up(x+1) - 1)
+
 /* prev log 2 of sz */
 static inline unsigned
 log2down(size_t sz)
 {
-
+	assert(sz > 0);
 	sz = bitsof(sz) - 1;
 	assert(sz <= UINT_MAX);
 	return ((unsigned) sz);