linux-kernel - [PATCH 4/9] drivers/iio: Sign extend without triggering implementation-defined behavior

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Message-Id: <20191028200700.213753-5-bvanassche@acm.org>
Date:   Mon, 28 Oct 2019 13:06:55 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Christoph Hellwig <hch@....de>,
        "Martin K . Petersen" <martin.petersen@...cle.com>,
        linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
        Bart Van Assche <bvanassche@....org>,
        Jonathan Cameron <jic23@...nel.org>,
        Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>
Subject: [PATCH 4/9] drivers/iio: Sign extend without triggering implementation-defined behavior

>From the C standard: "The result of E1 >> E2 is E1 right-shifted E2 bit
positions. If E1 has an unsigned type or if E1 has a signed type and a
nonnegative value, the value of the result is the integral part of the
quotient of E1 / 2E2 . If E1 has a signed type and a negative value, the
resulting value is implementation-defined."

Hence use sign_extend_24_to_32() instead of "<< 8 >> 8".

Cc: Jonathan Cameron <jic23@...nel.org>
Cc: Hartmut Knaack <knaack.h@....de>
Cc: Lars-Peter Clausen <lars@...afoo.de>
Cc: Peter Meerwald-Stadler <pmeerw@...erw.net>
Signed-off-by: Bart Van Assche <bvanassche@....org>
---
 drivers/iio/common/st_sensors/st_sensors_core.c | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/drivers/iio/common/st_sensors/st_sensors_core.c b/drivers/iio/common/st_sensors/st_sensors_core.c
index 4a3064fb6cd9..94a9cec69cd7 100644
--- a/drivers/iio/common/st_sensors/st_sensors_core.c
+++ b/drivers/iio/common/st_sensors/st_sensors_core.c
@@ -21,11 +21,6 @@
 
 #include "st_sensors_core.h"
 
-static inline u32 st_sensors_get_unaligned_le24(const u8 *p)
-{
-	return (s32)((p[0] | p[1] << 8 | p[2] << 16) << 8) >> 8;
-}
-
 int st_sensors_write_data_with_mask(struct iio_dev *indio_dev,
 				    u8 reg_addr, u8 mask, u8 data)
 {
@@ -556,7 +551,7 @@ static int st_sensors_read_axis_data(struct iio_dev *indio_dev,
 	else if (byte_for_channel == 2)
 		*data = (s16)get_unaligned_le16(outdata);
 	else if (byte_for_channel == 3)
-		*data = (s32)st_sensors_get_unaligned_le24(outdata);
+		*data = get_unaligned_signed_le24(outdata);
 
 st_sensors_free_memory:
 	kfree(outdata);
-- 
2.24.0.rc0.303.g954a862665-goog