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drivers: sensor: ltrf216a: fix overflow in conversion

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The conversion of the raw sensor value overflows because
only a 32 bit multiplication is executed.
Fix the issue by promoting the raw sensor value to uint64_t before
executing the multiplication.

Analysis:
The current implementation overflows for all raw values grater
than 9544(14-bit).
But according to the datasheet the sensor has a maximum resolution of
20-bit. So Multiplying that value with 450.000 would need at least 39
bit to avoid an overflow, hence do it using 64-bit arithmetic.

Fixes CID 330657

Signed-off-by: Thomas Stranger <thomas.stranger@outlook.com>
This commit is contained in:
Thomas Stranger 2024-02-11 17:32:57 +01:00 • committed by Henrik Brix Andersen
commit 61f065230a
1 changed files with 1 additions and 1 deletions
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drivers/sensor/ltrf216a/ltrf216a.c
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@ -127,7 +127,7 @@ static int ltrf216a_channel_get(const struct device *dev, enum sensor_channel ch
* 0.45 -> 45 / 100, multiplied by 1000000 for millilux
* gain 3 (default), integration time 100ms=1
*/
uint64_t microlux = (greendata * 45000 * LTRF216A_WIN_FAC * 10) / (3 * 1);
uint64_t microlux = ((uint64_t)greendata * 45000 * LTRF216A_WIN_FAC * 10) / (3 * 1);
val->val1 = microlux / 1000000;
val->val2 = microlux % 1000000;