Add cramlimit function

src/buddy.c

@@ -194,6 +194,27 @@ npages(size_t size, unsigned bits)
 	return (s);
 }
 
+/*
+ * limit a cram value such that an allocation returned by buddy can
+ * not be smaller than 1<<bits
+ */
+int8_t
+BUDDYF(cramlimit_bits)(size_t sz, int8_t cram, int8_t bits)
+{
+	int8_t up;
+
+	assert(sz >= (size_t)1 << bits);
+	if (cram == 0)
+		return (cram);
+	up = (int8_t)(uint8_t)log2up(sz);
+	assert(up >= bits);
+	up -= bits;
+	if (abs(cram) <= up)
+		return (cram);
+	return (cram < 0 ? 0 - up : up);
+}
+
+
 /************************************************************
  * init free map
  *
@@ -2030,6 +2051,40 @@ BUDDYF(return)(struct buddy_returns *rets)
 /************************************************************
  * tests
  */
+
+static void
+t_cramlimit(void)
+{
+	const int8_t min = 12;
+	int8_t cram, t, bits, l;
+	size_t sz;
+
+	for (cram = -10; cram <= 10; cram++) {
+		for (bits = min; bits < 20; bits++) {
+			// valid cram is bits - min
+			sz = (size_t)1 << bits;
+			t = BUDDYF(cramlimit_bits)(sz, cram, min);
+			l = bits - min;
+			assert(abs(t) <= l);
+			assert(t == 0 || (t < 0) == (cram < 0));
+
+			// test round up from pow2 + 1
+			sz++;
+			l++;
+			t = BUDDYF(cramlimit_bits)(sz, cram, min);
+			assert(abs(t) <= l);
+			assert(t == 0 || (t < 0) == (cram < 0));
+
+			// test round up from (pow2 + 1) - 1
+			sz = (size_t)1 << (bits + 1);
+			sz--;
+			t = BUDDYF(cramlimit_bits)(sz, cram, min);
+			assert(abs(t) <= l);
+			assert(t == 0 || (t < 0) == (cram < 0));
+		}
+	}
+}
+
 int t[] = {
 	-1,
 	255,
@@ -2732,6 +2787,7 @@ t_buddy(size_t free)
 
 int main(void)
 {
+	t_cramlimit();
 	t_bitf();
 	t_buddy(1 << 15);
 	t_buddy((1 << 15) - 1);

src/buddy.h

@@ -86,6 +86,7 @@ typedef struct BUDDY buddy_t;
  */
 void * BUDDYF(mmap)(size_t *, void *);
 void BUDDYF(unmap)(void **, size_t, void **);
+int8_t BUDDYF(cramlimit_bits)(size_t, int8_t, int8_t);
 static inline int
 abslimit(int val, int lim)
 {