From: Timo Sirainen <timo.sirainen@dovecot.fi>
Date: Tue, 18 Apr 2017 12:38:59 +0000 (+0300)
Subject: lib: Add bits_is_power_of_two()
X-Git-Tag: 2.2.30.rc1~77
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=cd955fdc0e2dbd7c282bea66804f277f9bbe2046;p=thirdparty%2Fdovecot%2Fcore.git

lib: Add bits_is_power_of_two()
---

diff --git a/src/lib/bits.h b/src/lib/bits.h
index b9e5f59f26..d030382267 100644
--- a/src/lib/bits.h
+++ b/src/lib/bits.h
@@ -8,6 +8,13 @@
 
 size_t nearest_power(size_t num) ATTR_CONST;
 
+/* Returns TRUE if 2^x=num, i.e. if num has only a single bit set to 1. */
+static inline bool ATTR_CONST
+bits_is_power_of_two(uint64_t num)
+{
+	return num > 0 && (num & (num - 1)) == 0;
+}
+
 #if __GNUC__ > 2
 static inline unsigned int ATTR_CONST
 bits_required32(uint32_t num)
diff --git a/src/lib/test-bits.c b/src/lib/test-bits.c
index b93848beeb..54756ed288 100644
--- a/src/lib/test-bits.c
+++ b/src/lib/test-bits.c
@@ -39,6 +39,20 @@ static void test_nearest_power(void)
 	test_end();
 }
 
+static void test_bits_is_power_of_two(void)
+{
+	test_begin("bits_is_power_of_two()");
+	for (unsigned int i = 0; i < 64; i++)
+		test_assert_idx(bits_is_power_of_two(1ULL << i), i);
+	for (unsigned int i = 2; i < 64; i++) {
+		test_assert_idx(!bits_is_power_of_two((1ULL << i) - 1), i);
+		test_assert_idx(!bits_is_power_of_two((1ULL << i) + 1), i);
+	}
+	test_assert(!bits_is_power_of_two(0));
+	test_assert(!bits_is_power_of_two(0xffffffffffffffffULL));
+	test_end();
+}
+
 static void test_bits_requiredXX(void) 
 {
 	/* As ..64 depends on ..32 and tests it twice,
@@ -86,6 +100,7 @@ static void test_sum_overflows(void)
 void test_bits()
 {
 	test_nearest_power();
+	test_bits_is_power_of_two();
 	test_bits_requiredXX();
 	test_sum_overflows();
 }