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Subject[PATCH v3 04/10] iio: afe: rescale: reduce risk of integer overflow
Date
From: Liam Beguin <lvb@xiphos.com>

Reduce the risk of integer overflow by doing the scale calculation with
64bit integers and looking for a Greatest Common Divider for both parts
of the fractional value.

Signed-off-by: Liam Beguin <lvb@xiphos.com>
---
drivers/iio/afe/iio-rescale.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/iio/afe/iio-rescale.c b/drivers/iio/afe/iio-rescale.c
index 774eb3044edd..98bcb5d418d6 100644
--- a/drivers/iio/afe/iio-rescale.c
+++ b/drivers/iio/afe/iio-rescale.c
@@ -39,7 +39,8 @@ static int rescale_read_raw(struct iio_dev *indio_dev,
int *val, int *val2, long mask)
{
struct rescale *rescale = iio_priv(indio_dev);
- unsigned long long tmp;
+ s64 tmp, tmp2;
+ u32 factor;
int ret;

switch (mask) {
@@ -67,8 +68,11 @@ static int rescale_read_raw(struct iio_dev *indio_dev,
}
switch (ret) {
case IIO_VAL_FRACTIONAL:
- *val *= rescale->numerator;
- *val2 *= rescale->denominator;
+ tmp = (s64)*val * rescale->numerator;
+ tmp2 = (s64)*val2 * rescale->denominator;
+ factor = gcd(tmp, tmp2);
+ *val = tmp / factor;
+ *val2 = tmp2 / factor;
return ret;
case IIO_VAL_INT:
*val *= rescale->numerator;
--
2.30.1.489.g328c10930387
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