[RESEND v7 1/4] media: v4l: move helper functions for fractions from uvc to v4l2-common

Michael Grzeschik
2022-06-08T10:57:58Z

The functions uvc_simplify_fraction and uvc_fraction_to_interval are
generic helpers which are also useful for other v4l2 drivers. This patch
moves them to v4l2-common.

Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>

---
v1 -> v7: -

drivers/media/usb/uvc/uvc_driver.c | 80 --------------------------
drivers/media/usb/uvc/uvc_v4l2.c | 14 ++---
drivers/media/usb/uvc/uvcvideo.h | 3 -
drivers/media/v4l2-core/v4l2-common.c | 82 +++++++++++++++++++++++++++
include/media/v4l2-common.h | 4 ++
5 files changed, 93 insertions(+), 90 deletions(-)

diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
index 6c86faecbea21e..2bf7f524e130bc 100644
--- a/drivers/media/usb/uvc/uvc_driver.c
+++ b/drivers/media/usb/uvc/uvc_driver.c
@@ -329,86 +329,6 @@ static enum v4l2_ycbcr_encoding uvc_ycbcr_enc(const u8 matrix_coefficients)
return V4L2_YCBCR_ENC_DEFAULT; /* Reserved */
}

-/* Simplify a fraction using a simple continued fraction decomposition. The
- * idea here is to convert fractions such as 333333/10000000 to 1/30 using
- * 32 bit arithmetic only. The algorithm is not perfect and relies upon two
- * arbitrary parameters to remove non-significative terms from the simple
- * continued fraction decomposition. Using 8 and 333 for n_terms and threshold
- * respectively seems to give nice results.
- */
-void uvc_simplify_fraction(u32 *numerator, u32 *denominator,
- unsigned int n_terms, unsigned int threshold)
-{
- u32 *an;
- u32 x, y, r;
- unsigned int i, n;
-
- an = kmalloc_array(n_terms, sizeof(*an), GFP_KERNEL);
- if (an == NULL)
- return;
-
- /* Convert the fraction to a simple continued fraction. See
- * https://mathforum.org/dr.math/faq/faq.fractions.html
- * Stop if the current term is bigger than or equal to the given
- * threshold.
- */
- x = *numerator;
- y = *denominator;
-
- for (n = 0; n < n_terms && y != 0; ++n) {
- an[n] = x / y;
- if (an[n] >= threshold) {
- if (n < 2)
- n++;
- break;
- }
-
- r = x - an[n] * y;
- x = y;
- y = r;
- }
-
- /* Expand the simple continued fraction back to an integer fraction. */
- x = 0;
- y = 1;
-
- for (i = n; i > 0; --i) {
- r = y;
- y = an[i-1] * y + x;
- x = r;
- }
-
- *numerator = y;
- *denominator = x;
- kfree(an);
-}
-
-/* Convert a fraction to a frame interval in 100ns multiples. The idea here is
- * to compute numerator / denominator * 10000000 using 32 bit fixed point
- * arithmetic only.
- */
-u32 uvc_fraction_to_interval(u32 numerator, u32 denominator)
-{
- u32 multiplier;
-
- /* Saturate the result if the operation would overflow. */
- if (denominator == 0 ||
- numerator/denominator >= ((u32)-1)/10000000)
- return (u32)-1;
-
- /* Divide both the denominator and the multiplier by two until
- * numerator * multiplier doesn't overflow. If anyone knows a better
- * algorithm please let me know.
- */
- multiplier = 10000000;
- while (numerator > ((u32)-1)/multiplier) {
- multiplier /= 2;
- denominator /= 2;
- }
-
- return denominator ? numerator * multiplier / denominator : 0;
-}
-
/* ------------------------------------------------------------------------
* Terminal and unit management
*/
diff --git a/drivers/media/usb/uvc/uvc_v4l2.c b/drivers/media/usb/uvc/uvc_v4l2.c
index 648dcd579e8155..26cf0517e36195 100644
--- a/drivers/media/usb/uvc/uvc_v4l2.c
+++ b/drivers/media/usb/uvc/uvc_v4l2.c
@@ -382,7 +382,7 @@ static int uvc_v4l2_get_streamparm(struct uvc_streaming *stream,
mutex_unlock(&stream->mutex);

denominator = 10000000;
- uvc_simplify_fraction(&numerator, &denominator, 8, 333);
+ v4l2_simplify_fraction(&numerator, &denominator, 8, 333);

memset(parm, 0, sizeof(*parm));
parm->type = stream->type;
@@ -423,7 +423,7 @@ static int uvc_v4l2_set_streamparm(struct uvc_streaming *stream,
else
timeperframe = parm->parm.output.timeperframe;

- interval = uvc_fraction_to_interval(timeperframe.numerator,
+ interval = v4l2_fraction_to_interval(timeperframe.numerator,
timeperframe.denominator);
uvc_dbg(stream->dev, FORMAT, "Setting frame interval to %u/%u (%u)\n",
timeperframe.numerator, timeperframe.denominator, interval);
@@ -477,7 +477,7 @@ static int uvc_v4l2_set_streamparm(struct uvc_streaming *stream,
/* Return the actual frame period. */
timeperframe.numerator = probe.dwFrameInterval;
timeperframe.denominator = 10000000;
- uvc_simplify_fraction(&timeperframe.numerator,
+ v4l2_simplify_fraction(&timeperframe.numerator,
&timeperframe.denominator, 8, 333);

if (parm->type == V4L2_BUF_TYPE_VIDEO_CAPTURE) {
@@ -1271,7 +1271,7 @@ static int uvc_ioctl_enum_frameintervals(struct file *file, void *fh,
fival->discrete.numerator =
frame->dwFrameInterval[index];
fival->discrete.denominator = 10000000;
- uvc_simplify_fraction(&fival->discrete.numerator,
+ v4l2_simplify_fraction(&fival->discrete.numerator,
&fival->discrete.denominator, 8, 333);
} else {
fival->type = V4L2_FRMIVAL_TYPE_STEPWISE;
@@ -1281,11 +1281,11 @@ static int uvc_ioctl_enum_frameintervals(struct file *file, void *fh,
fival->stepwise.max.denominator = 10000000;
fival->stepwise.step.numerator = frame->dwFrameInterval[2];
fival->stepwise.step.denominator = 10000000;
- uvc_simplify_fraction(&fival->stepwise.min.numerator,
+ v4l2_simplify_fraction(&fival->stepwise.min.numerator,
&fival->stepwise.min.denominator, 8, 333);
- uvc_simplify_fraction(&fival->stepwise.max.numerator,
+ v4l2_simplify_fraction(&fival->stepwise.max.numerator,
&fival->stepwise.max.denominator, 8, 333);
- uvc_simplify_fraction(&fival->stepwise.step.numerator,
+ v4l2_simplify_fraction(&fival->stepwise.step.numerator,
&fival->stepwise.step.denominator, 8, 333);
}

diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
index c5b4febd2d94b6..ec3f8ec0e25ca3 100644
--- a/drivers/media/usb/uvc/uvcvideo.h
+++ b/drivers/media/usb/uvc/uvcvideo.h
@@ -909,9 +909,6 @@ int uvc_xu_ctrl_query(struct uvc_video_chain *chain,
struct uvc_xu_control_query *xqry);

/* Utility functions */
-void uvc_simplify_fraction(u32 *numerator, u32 *denominator,
- unsigned int n_terms, unsigned int threshold);
-u32 uvc_fraction_to_interval(u32 numerator, u32 denominator);
struct usb_host_endpoint *uvc_find_endpoint(struct usb_host_interface *alts,
u8 epaddr);
u16 uvc_endpoint_max_bpi(struct usb_device *dev, struct usb_host_endpoint *ep);
diff --git a/drivers/media/v4l2-core/v4l2-common.c b/drivers/media/v4l2-core/v4l2-common.c
index df34b2a283bc29..1d0b56249ca0e1 100644
--- a/drivers/media/v4l2-core/v4l2-common.c
+++ b/drivers/media/v4l2-core/v4l2-common.c
@@ -482,3 +482,85 @@ s64 v4l2_get_link_freq(struct v4l2_ctrl_handler *handler, unsigned int mul,
return freq > 0 ? freq : -EINVAL;
}
EXPORT_SYMBOL_GPL(v4l2_get_link_freq);
+
+/* Simplify a fraction using a simple continued fraction decomposition. The
+ * idea here is to convert fractions such as 333333/10000000 to 1/30 using
+ * 32 bit arithmetic only. The algorithm is not perfect and relies upon two
+ * arbitrary parameters to remove non-significative terms from the simple
+ * continued fraction decomposition. Using 8 and 333 for n_terms and threshold
+ * respectively seems to give nice results.
+ */
+void v4l2_simplify_fraction(u32 *numerator, u32 *denominator,
+ unsigned int n_terms, unsigned int threshold)
+{
+ u32 *an;
+ u32 x, y, r;
+ unsigned int i, n;
+
+ an = kmalloc_array(n_terms, sizeof(*an), GFP_KERNEL);
+ if (an == NULL)
+ return;
+
+ /* Convert the fraction to a simple continued fraction. See
+ * https://mathforum.org/dr.math/faq/faq.fractions.html
+ * Stop if the current term is bigger than or equal to the given
+ * threshold.
+ */
+ x = *numerator;
+ y = *denominator;
+
+ for (n = 0; n < n_terms && y != 0; ++n) {
+ an[n] = x / y;
+ if (an[n] >= threshold) {
+ if (n < 2)
+ n++;
+ break;
+ }
+
+ r = x - an[n] * y;
+ x = y;
+ y = r;
+ }
+
+ /* Expand the simple continued fraction back to an integer fraction. */
+ x = 0;
+ y = 1;
+
+ for (i = n; i > 0; --i) {
+ r = y;
+ y = an[i-1] * y + x;
+ x = r;
+ }
+
+ *numerator = y;
+ *denominator = x;
+ kfree(an);
+}
+EXPORT_SYMBOL_GPL(v4l2_simplify_fraction);
+
+/* Convert a fraction to a frame interval in 100ns multiples. The idea here is
+ * to compute numerator / denominator * 10000000 using 32 bit fixed point
+ * arithmetic only.
+ */
+u32 v4l2_fraction_to_interval(u32 numerator, u32 denominator)
+{
+ u32 multiplier;
+
+ /* Saturate the result if the operation would overflow. */
+ if (denominator == 0 ||
+ numerator/denominator >= ((u32)-1)/10000000)
+ return (u32)-1;
+
+ /* Divide both the denominator and the multiplier by two until
+ * numerator * multiplier doesn't overflow. If anyone knows a better
+ * algorithm please let me know.
+ */
+ multiplier = 10000000;
+ while (numerator > ((u32)-1)/multiplier) {
+ multiplier /= 2;
+ denominator /= 2;
+ }
+
+ return denominator ? numerator * multiplier / denominator : 0;
+}
+EXPORT_SYMBOL_GPL(v4l2_fraction_to_interval);
diff --git a/include/media/v4l2-common.h b/include/media/v4l2-common.h
index 3eb202259e8ccd..df4ad81251195e 100644
--- a/include/media/v4l2-common.h
+++ b/include/media/v4l2-common.h
@@ -540,6 +540,10 @@ int v4l2_fill_pixfmt_mp(struct v4l2_pix_format_mplane *pixfmt, u32 pixelformat,
s64 v4l2_get_link_freq(struct v4l2_ctrl_handler *handler, unsigned int mul,
unsigned int div);

+void v4l2_simplify_fraction(u32 *numerator, u32 *denominator,
+ unsigned int n_terms, unsigned int threshold);
+u32 v4l2_fraction_to_interval(u32 numerator, u32 denominator);
+
static inline u64 v4l2_buffer_get_timestamp(const struct v4l2_buffer *buf)
{
/*
--
2.30.2