ASoC: nau8824: use 64-bit arithmetic instead of 32-bit
diff mbox

Message ID 20180705130617.GA31233@embeddedor.com
State Accepted
Commit f7ddff54d0a0f068442414b48bec7f22aa777de7
Headers show

Commit Message

Gustavo A. R. Silva July 5, 2018, 1:06 p.m. UTC
Add suffix ULL to constant 256 in order to give the compiler complete
information about the proper arithmetic to use.

Notice that such constant is used in a context that expects an
expression of type u64 (64 bits, unsigned) and the following
expression is currently being evaluated using 32-bit arithmetic:

256 * fs * 2 * mclk_src_scaling[i].param

Addresses-Coverity-ID: 1432039 ("Unintentional integer overflow")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
---
 sound/soc/codecs/nau8824.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Trent Piepho July 6, 2018, 2:09 a.m. UTC | #1
On Thu, Jul 5, 2018 at 6:06 AM, Gustavo A. R. Silva
<gustavo@embeddedor.com> wrote:
> Add suffix ULL to constant 256 in order to give the compiler complete
> information about the proper arithmetic to use.
>
> Notice that such constant is used in a context that expects an
> expression of type u64 (64 bits, unsigned) and the following
> expression is currently being evaluated using 32-bit arithmetic:
>
> 256 * fs * 2 * mclk_src_scaling[i].param
>
> Addresses-Coverity-ID: 1432039 ("Unintentional integer overflow")
> Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
> ---
>  sound/soc/codecs/nau8824.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/sound/soc/codecs/nau8824.c b/sound/soc/codecs/nau8824.c
> index 6bd1445..468d514 100644
> --- a/sound/soc/codecs/nau8824.c
> +++ b/sound/soc/codecs/nau8824.c
> @@ -1274,7 +1274,7 @@ static int nau8824_calc_fll_param(unsigned int fll_in,
>         fvco_max = 0;
>         fvco_sel = ARRAY_SIZE(mclk_src_scaling);
>         for (i = 0; i < ARRAY_SIZE(mclk_src_scaling); i++) {
> -               fvco = 256 * fs * 2 * mclk_src_scaling[i].param;
> +               fvco = 256ULL * fs * 2 * mclk_src_scaling[i].param;

This would be better written as fvco = (256 * 2 *
mclk_src_scaling[i].param) * (u64)fs;

There no reason the entire expression must use 64 bit multiplies,
since the left side
above is know to fit in 32-bits.

The code could be more efficient if mclk_src_scaling had been sorted
by scaling ratio
instead of register value.  In fact, most of the math in this loop
could be precomputed by the
compiler if one instead though of min and max fs range for a given scaler.

Patch
diff mbox

diff --git a/sound/soc/codecs/nau8824.c b/sound/soc/codecs/nau8824.c
index 6bd1445..468d514 100644
--- a/sound/soc/codecs/nau8824.c
+++ b/sound/soc/codecs/nau8824.c
@@ -1274,7 +1274,7 @@  static int nau8824_calc_fll_param(unsigned int fll_in,
 	fvco_max = 0;
 	fvco_sel = ARRAY_SIZE(mclk_src_scaling);
 	for (i = 0; i < ARRAY_SIZE(mclk_src_scaling); i++) {
-		fvco = 256 * fs * 2 * mclk_src_scaling[i].param;
+		fvco = 256ULL * fs * 2 * mclk_src_scaling[i].param;
 		if (fvco > NAU_FVCO_MIN && fvco < NAU_FVCO_MAX &&
 			fvco_max < fvco) {
 			fvco_max = fvco;