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From: Richard Fitzgerald <rf@opensource.cirrus.com>
To: <pmladek@suse.com>, <rostedt@goodmis.org>,
	<sergey.senozhatsky@gmail.com>,
	<andriy.shevchenko@linux.intel.com>, <linux@rasmusvillemoes.dk>,
	<w@1wt.eu>, <davem@davemloft.net>, <kuba@kernel.org>
Cc: <netdev@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
	<patches@opensource.cirrus.com>,
	Richard Fitzgerald <rf@opensource.cirrus.com>
Subject: [PATCH v2 1/2] lib: test_scanf: Remove pointless use of type_min() with unsigned types
Date: Tue, 25 May 2021 12:05:45 +0100	[thread overview]
Message-ID: <20210525110546.6223-2-rf@opensource.cirrus.com> (raw)
In-Reply-To: <20210525110546.6223-1-rf@opensource.cirrus.com>

sparse was producing warnings of the form:

 sparse: cast truncates bits from constant value (ffff0001 becomes 1)

There is no actual problem here. Using type_min() on an unsigned type
results in an (expected) truncation.

However, there is no need to test an unsigned value against type_min().
The minimum value of an unsigned is obviously 0, and any value cast to
an unsigned type is >= 0, so for unsigneds only type_max() need be tested.

This patch also takes the opportunity to clean up the implementation of
simple_numbers_loop() to use a common pattern for the positive and
negative test.

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
---
 lib/test_scanf.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/lib/test_scanf.c b/lib/test_scanf.c
index 8d577aec6c28..48ff5747a4da 100644
--- a/lib/test_scanf.c
+++ b/lib/test_scanf.c
@@ -187,8 +187,8 @@ static const unsigned long long numbers[] __initconst = {
 #define value_representable_in_type(T, val)					 \
 (is_signed_type(T)								 \
 	? ((long long)(val) >= type_min(T)) && ((long long)(val) <= type_max(T)) \
-	: ((unsigned long long)(val) >= type_min(T)) &&				 \
-	  ((unsigned long long)(val) <= type_max(T)))
+	: ((unsigned long long)(val) <= type_max(T)))
+
 
 #define test_one_number(T, gen_fmt, scan_fmt, val, fn)			\
 do {									\
@@ -204,12 +204,11 @@ do {									\
 	int i;								\
 									\
 	for (i = 0; i < ARRAY_SIZE(numbers); i++) {			\
-		if (!value_representable_in_type(T, numbers[i]))	\
-			continue;					\
+		if (value_representable_in_type(T, numbers[i]))		\
+			test_one_number(T, gen_fmt, scan_fmt,		\
+					numbers[i], fn);		\
 									\
-		test_one_number(T, gen_fmt, scan_fmt, numbers[i], fn);	\
-									\
-		if (is_signed_type(T))					\
+		if (value_representable_in_type(T, -numbers[i]))	\
 			test_one_number(T, gen_fmt, scan_fmt,		\
 					-numbers[i], fn);		\
 	}								\
-- 
2.20.1


  reply	other threads:[~2021-05-25 11:07 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-25 11:05 [PATCH v2 0/2] Fix truncation warnings from building test_scanf.c Richard Fitzgerald
2021-05-25 11:05 ` Richard Fitzgerald [this message]
  -- strict thread matches above, loose matches on Subject: below --
2021-05-25 12:20 Richard Fitzgerald
2021-05-25 12:20 ` [PATCH v2 1/2] lib: test_scanf: Remove pointless use of type_min() with unsigned types Richard Fitzgerald

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