media: v4l: move helper functions for fractions from uvc to v4l2-common

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.
Tested-by: Daniel Scally <dan.scally@ideasonboard.com>
Reviewed-by: Daniel Scally <dan.scally@ideasonboard.com>
Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
Link: https://lore.kernel.org/r/20220909221335.15033-2-m.grzeschik@pengutronix.deSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/media/usb/uvc/uvc_driver.c

@@ -329,90 +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://en.wikipedia.org/wiki/Continued_fraction
-	 * 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
  */

drivers/media/usb/uvc/uvc_v4l2.c

@@ -386,7 +386,7 @@ 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;
@@ -427,7 +427,7 @@ 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);
@@ -481,7 +481,7 @@ 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) {
@@ -1275,7 +1275,7 @@ 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;
@@ -1285,11 +1285,11 @@ 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);
 	}
 

drivers/media/usb/uvc/uvcvideo.h

@@ -911,9 +911,6 @@ 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);

drivers/media/v4l2-core/v4l2-common.c

@@ -484,3 +484,89 @@ 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://en.wikipedia.org/wiki/Continued_fraction
+	 * 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);

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)
 {
 	/*