lib: bits - macros to simplify expressions when using -Wstrict-bool

To be strict-bool compliant, your expressions need to be a bit verbose,
these might simplify things.

There are presently over 400 instances matching HAS_NO_BITS(), and nearly
1300 instances matching HAS_ANY_BITS(), so it's a very common pattern.

Signed-off-by: Phil Carmody <phil@dovecot.fi>

src/lib/bits.h

@@ -6,6 +6,17 @@
 
 #define BIT(n) (1u << (n))
 
+/* These expressions make it easy to ensure that bit test expressions
+   are boolean in order to satisfy the in-house -Wstrict-bool. */
+/* ((val & bits) == 0) is very common */
+#define HAS_NO_BITS(val,bits) (((val) & (bits)) == 0)
+/* ((val & bits) != 0) is even more common */
+/* Note - illogical behaviour if bits==0, fixing that requires potential
+   multiple evaluation, but it's a corner case that should never occur. */
+#define HAS_ANY_BITS(val,bits) (((val) & (bits)) != 0)
+/* ((val & bits) == bits) is uncommon */
+#define HAS_ALL_BITS(val,bits) ((~(val) & (bits)) == 0)
+
 /* Returns x, such that x is the smallest power of 2 >= num. */
 size_t nearest_power(size_t num) ATTR_CONST;
 

src/lib/test-bits.c

@@ -190,6 +190,35 @@ static void test_bits_rotr64(void)
 	test_end();
 }
 
+static void test_bit_tests(void)
+{
+	test_begin("HAS_..._BITS() macro tests");
+
+	test_assert(HAS_NO_BITS(1,0));
+	test_assert(HAS_NO_BITS(2,~2));
+	test_assert(!HAS_NO_BITS(2,2));
+
+	/* OUCH - this vacuously true expression fails. However, if you are
+	   dumb enough to use 0 as bits, then it will also fail in the verbose
+	   case that this macro replaces, it's not a regression. */
+	/* test_assert(HAS_ANY_BITS(6,0)); */
+	test_assert(HAS_ANY_BITS(3,1));
+	test_assert(HAS_ANY_BITS(2,3));
+	test_assert(!HAS_ANY_BITS(7,~(7|128)));
+
+	test_assert(HAS_ALL_BITS(0,0));
+	test_assert(HAS_ALL_BITS(30,14));
+	test_assert(!HAS_ALL_BITS(~1,~0));
+
+	/* Trap double-evaluation */
+	unsigned int v=10,b=2;
+	test_assert(!HAS_NO_BITS(v++, b++) && v==11 && b==3);
+	test_assert(HAS_ANY_BITS(v++, b++) && v==12 && b==4);
+	test_assert(HAS_ALL_BITS(v++, b++) && v==13 && b==5);
+
+	test_end();
+}
+
 void test_bits(void)
 {
 	test_nearest_power();
@@ -202,4 +231,5 @@ void test_bits(void)
 	test_bits_rotl64();
 	test_bits_rotr64();
 	test_sum_overflows();
+	test_bit_tests();
 }