tlv: implement nearest rounding in snd_tlv_convert_from_dB() for xdir == 0

We should round-up values to nearest to get more precise results.

BugLink: https://github.com/alsa-project/alsa-utils/issues/35
Signed-off-by: Jaroslav Kysela <perex@perex.cz>

2 files changed, 20 insertions, 7 deletions

diff --git a/src/control/tlv.c b/src/control/tlv.c
index d6944b52..d5044eb5 100644
--- a/src/control/tlv.c
+++ b/src/control/tlv.c
@@ -286,7 +286,8 @@ int snd_tlv_convert_to_dB(unsigned int *tlv, long rangemin, long rangemax,
  * \param db_gain the dB gain to convert (in 0.01dB unit)
  * \param value the pointer to store the converted raw volume value
  * \param xdir the direction for round-up. The value is round up
- *        when this is positive.
+ *        when this is positive. A negative value means round down.
+ *        Zero means round-up to nearest.
  * \return 0 if successful, or a negative error code
  */
 int snd_tlv_convert_from_dB(unsigned int *tlv, long rangemin, long rangemax,
@@ -346,6 +347,8 @@ int snd_tlv_convert_from_dB(unsigned int *tlv, long rangemin, long rangemax,
 			long v = (db_gain - min) * (rangemax - rangemin);
 			if (xdir > 0)
 				v += (max - min) - 1;
+			else if (xdir == 0)
+				v += ((max - min) + 1) / 2;
 			v = v / (max - min) + rangemin;
 			*value = v;
 		}
@@ -368,6 +371,8 @@ int snd_tlv_convert_from_dB(unsigned int *tlv, long rangemin, long rangemax,
 			long v = (db_gain - min) * (rangemax - rangemin);
 			if (xdir > 0)
 				v += (max - min) - 1;
+			else if (xdir == 0)
+				v += ((max - min) + 1) / 2;
 			v = v / (max - min) + rangemin;
 			*value = v;
 		}
@@ -392,6 +397,8 @@ int snd_tlv_convert_from_dB(unsigned int *tlv, long rangemin, long rangemax,
 			v = (v - vmin) * (rangemax - rangemin) / (vmax - vmin);
 			if (xdir > 0)
 				v = ceil(v);
+			else if (xdir == 0)
+				v = lrint(v);
 			*value = (long)v + rangemin;
 		}
 		return 0;
diff --git a/src/mixer/simple.c b/src/mixer/simple.c
index 2861d97c..571fa664 100644
--- a/src/mixer/simple.c
+++ b/src/mixer/simple.c
@@ -376,7 +376,8 @@ int snd_mixer_selem_ask_playback_vol_dB(snd_mixer_elem_t *elem, long value, long
  * \brief Return corresponding integer playback volume for given dB value for a mixer simple element
  * \param elem Mixer simple element handle
  * \param value value to be converted to dB range
- * \param dir rounding mode - rounds up if dir > 0, otherwise rounds down
+ * \param dir rounding mode - rounds up if dir > 0, round to nearest if dir == 0,
+ *            rounds down if dir < 0
  * \param dBvalue pointer to returned dB value
  * \return 0 on success otherwise a negative error code
  */
@@ -454,7 +455,8 @@ int snd_mixer_selem_set_playback_volume(snd_mixer_elem_t *elem, snd_mixer_selem_
  * \param elem Mixer simple element handle
  * \param channel mixer simple element channel identifier
  * \param value control value in dB * 100
- * \param dir rounding mode - rounds up if dir > 0, otherwise rounds down
+ * \param dir rounding mode - rounds up if dir > 0, round to nearest if dir == 0,
+ *            rounds down if dir < 0
  * \return 0 on success otherwise a negative error code
  */
 int snd_mixer_selem_set_playback_dB(snd_mixer_elem_t *elem, snd_mixer_selem_channel_id_t channel, long value, int dir)
@@ -491,7 +493,8 @@ int snd_mixer_selem_set_playback_volume_all(snd_mixer_elem_t *elem, long value)
  * \brief Set value in dB of playback volume control for all channels of a mixer simple element
  * \param elem Mixer simple element handle
  * \param value control value in dB * 100
- * \param dir rounding mode - rounds up if dir > 0, otherwise rounds down
+ * \param dir rounding mode - rounds up if dir > 0, round to nearest if dir == 0,
+ *            rounds down if dir < 0
  * \return 0 on success otherwise a negative error code
  */
 int snd_mixer_selem_set_playback_dB_all(snd_mixer_elem_t *elem, long value, int dir)
@@ -706,7 +709,8 @@ int snd_mixer_selem_ask_capture_vol_dB(snd_mixer_elem_t *elem, long value, long
  * \param elem Mixer simple element handle
  * \param dBvalue dB value to be converted to integer range
  * \param value pointer to returned integer value
- * \param dir rounding mode - rounds up if dir > 0, otherwise rounds down
+ * \param dir rounding mode - rounds up if dir > 0, round to nearest if dir == 0,
+ *            rounds down if dir < 0
  * \return 0 on success otherwise a negative error code
  */
 int snd_mixer_selem_ask_capture_dB_vol(snd_mixer_elem_t *elem, long dBvalue, int dir, long *value)
@@ -777,7 +781,8 @@ int snd_mixer_selem_set_capture_volume(snd_mixer_elem_t *elem, snd_mixer_selem_c
  * \param elem Mixer simple element handle
  * \param channel mixer simple element channel identifier
  * \param value control value in dB * 100
- * \param dir rounding mode - rounds up if dir > 0, otherwise rounds down
+ * \param dir rounding mode - rounds up if dir > 0, round to nearest if dir == 0,
+ *            rounds down if dir < 0
  * \return 0 on success otherwise a negative error code
  */
 int snd_mixer_selem_set_capture_dB(snd_mixer_elem_t *elem, snd_mixer_selem_channel_id_t channel, long value, int dir)
@@ -814,7 +819,8 @@ int snd_mixer_selem_set_capture_volume_all(snd_mixer_elem_t *elem, long value)
  * \brief Set value in dB of capture volume control for all channels of a mixer simple element
  * \param elem Mixer simple element handle
  * \param value control value in dB * 100
- * \param dir rounding mode - rounds up if dir > 0, otherwise rounds down
+ * \param dir rounding mode - rounds up if dir > 0, round to nearest if dir == 0,
+ *            rounds down if dir < 0
  * \return 0 on success otherwise a negative error code
  */
 int snd_mixer_selem_set_capture_dB_all(snd_mixer_elem_t *elem, long value, int dir)