[34-longterm 208/247] hwmon: (sht15) Fix integer overflow in humidity calculation

Paul Gortmaker
2011-06-23T17:49:16Z

From: Vivien Didelot <vivien.didelot@savoirfairelinux.com>

-------------------
This is a commit scheduled for the next v2.6.34 longterm release.
If you see a problem with using this for longterm, please comment.
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commit ccd32e735de7a941906e093f8dca924bb05c5794 upstream.

An integer overflow occurs in the calculation of RHlinear when the
relative humidity is greater than around 30%. The consequence is a subtle
(but noticeable) error in the resulting humidity measurement.

Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: Jean Delvare <khali@linux-fr.org>
Cc: Jonathan Cameron <jic23@cam.ac.uk>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
---
drivers/hwmon/sht15.c | 4 ++--
1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/hwmon/sht15.c b/drivers/hwmon/sht15.c
index a610e78..38a41d2 100644
--- a/drivers/hwmon/sht15.c
+++ b/drivers/hwmon/sht15.c
@@ -333,11 +333,11 @@ static inline int sht15_calc_humid(struct sht15_data *data)

const int c1 = -4;
const int c2 = 40500; /* x 10 ^ -6 */
- const int c3 = -2800; /* x10 ^ -9 */
+ const int c3 = -28; /* x 10 ^ -7 */

RHlinear = c1*1000
+ c2 * data->val_humid/1000
- + (data->val_humid * data->val_humid * c3)/1000000;
+ + (data->val_humid * data->val_humid * c3) / 10000;
return (temp - 25000) * (10000 + 80 * data->val_humid)
/ 1000000 + RHlinear;
}
--
1.7.4.4