For BITF_NOIDX, sz_nbits() becomes trivial

src/bitf.h

@@ -134,6 +134,9 @@ sz_nbits(const size_t sz, const size_t index_thr)
 	assert(sz >= bitf_sz1(1));
 	assert(sz < (size_t)1 << 62);	// otherwise overflow
 
+	if (index_thr == BITF_NOIDX)
+		return (((sz - sizeof(struct bitf)) / wsz) * wbits);
+
 	lo = sz_nbits_est(sz) / wbits;
 	trysz = bitf_sz(lo * wbits, index_thr);
 

src/buddy.c

@@ -2258,22 +2258,37 @@ t_bitf(void)
 	free(mem);
 }
 
+#define ASSERT_NBITS_SZ_NOIDX(sz) do {					\
+	size_t bits = sz_nbits(sz, BITF_NOIDX);				\
+	assert(bitf_sz(bits, BITF_NOIDX) <= sz);			\
+									\
+	bits += wbits;							\
+	assert(bitf_sz(bits, BITF_NOIDX) > sz);			\
+	} while(0)
+
 static void
 t_sz_nbits(void)
 {
 	size_t u, v, sz;
 
-	for (u = 6; u < 32; u++)
+	for (u = 6; u < 32; u++) {
+		ASSERT_NBITS_SZ_NOIDX((size_t)1 << u);
 		(void) sz_nbits((size_t)1 << u, BITF_INDEX);
+	}
 
-	for (sz = 64; sz < 128; sz++)
+	for (sz = 64; sz < 128; sz++) {
+		ASSERT_NBITS_SZ_NOIDX(sz);
 		(void) sz_nbits(sz, BITF_INDEX);
+	}
 
-	for (u = 7; u < 61; u++)
+	for (u = 7; u < 61; u++) {
 		for (v = ((size_t)1 << u) - 32;
 		     v < ((size_t)1 << u) + 128;
-		     v += 8)
+		     v += 8) {
+			ASSERT_NBITS_SZ_NOIDX(v);
 			(void) sz_nbits(v, BITF_INDEX);
+		}
+	}
 }
 
 static size_t