From: Timo Sirainen <tss@iki.fi>
Date: Wed, 2 Jul 2014 17:13:35 +0000 (+0300)
Subject: lib: Added UINT64_SUM_OVERFLOWS()
X-Git-Tag: 2.2.14.rc1~306
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=cbc01fc844fa307e565cc81fd78536d7afca05a9;p=thirdparty%2Fdovecot%2Fcore.git

lib: Added UINT64_SUM_OVERFLOWS()
Maybe the unit tests are kind of unnecessary since the macro is so simple,
but at least it's now a well tested simple macro :)
---

diff --git a/src/lib/bits.h b/src/lib/bits.h
index 528152a064..5c6b768d71 100644
--- a/src/lib/bits.h
+++ b/src/lib/bits.h
@@ -12,6 +12,9 @@
 #include <stddef.h>
 #include <stdint.h>
 
+#define UINT64_SUM_OVERFLOWS(a, b) \
+	(a > (uint64_t)-1 - b)
+
 size_t nearest_power(size_t num) ATTR_CONST;
 
 unsigned int bits_required8(uint8_t num) ATTR_CONST;
diff --git a/src/lib/test-bits.c b/src/lib/test-bits.c
index 67ecb58405..46f2054398 100644
--- a/src/lib/test-bits.c
+++ b/src/lib/test-bits.c
@@ -60,8 +60,32 @@ static void test_bits_requiredXX(void)
 	test_end();
 }
 
+static void test_sum_overflows(void)
+{
+#define MAX64 (uint64_t)-1
+	static const struct {
+		uint64_t a, b;
+		bool overflows;
+	} tests[] = {
+		{ MAX64-1, 1, FALSE },
+		{ MAX64, 1, TRUE },
+		{ MAX64-1, 1, FALSE },
+		{ MAX64-1, 2, TRUE },
+		{ MAX64-1, MAX64-1, TRUE },
+		{ MAX64-1, MAX64, TRUE },
+		{ MAX64, MAX64, TRUE }
+	};
+	unsigned int i;
+
+	test_begin("UINT64_SUM_OVERFLOWS");
+	for (i = 0; i < N_ELEMENTS(tests); i++)
+		test_assert(UINT64_SUM_OVERFLOWS(tests[i].a, tests[i].b) == tests[i].overflows);
+	test_end();
+}
+
 void test_bits()
 {
 	test_nearest_power();
 	test_bits_requiredXX();
+	test_sum_overflows();
 }