mixer/alsa: work around rounding error at volume 0

Due to rounding errors, a slightly negative value can be passed to set_normalized_volume(), which will make the log10() call fail. Actually, volume 0 is already failing because log10(0) is illegal. So let's fix this by implementing two corner cases: <=0 and >=100. Closes #212

mixer/alsa: work around rounding error at volume 0
bede5646 · Max Kellermann · e0ca4b86 · bede5646 · bede5646
Commit bede5646 authored Feb 10, 2018 by Max Kellermann
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NEWS NEWS +2 -0

volume_mapping.c src/mixer/plugins/volume_mapping.c +7 -0

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--- a/NEWS
+++ b/NEWS
 ver 0.20.17 (not yet released)
 * output
  - alsa: fix crash bug with 8 channels
+* mixer
+  - alsa: fix rounding error at volume 0
 * fix real-time and idle scheduling with Musl
 * Android
  - fix compatibility with Android 4.0

--- a/src/mixer/plugins/volume_mapping.c
+++ b/src/mixer/plugins/volume_mapping.c
@@ -139,6 +139,13 @@ static int set_normalized_volume(snd_mixer_elem_t *elem,
 		return set_raw[ctl_dir](elem, value);
 	}

+	/* two special cases to avoid rounding errors at 0% and
+	   100% */
+	if (volume <= 0)
+		return set_dB[ctl_dir](elem, min, dir);
+	else if (volume >= 100)
+		return set_dB[ctl_dir](elem, max, dir);
+
 	if (use_linear_dB_scale(min, max)) {
 		value = lrint_dir(volume * (max - min), dir) + min;
 		return set_dB[ctl_dir](elem, value, dir);