linux-kernel - [PATCH] ALSA: echoaudio: simplify get_audio

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Date:   Sat,  7 Dec 2019 14:49:53 -0800
From:   Olof Johansson <olof@...om.net>
To:     Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>
Cc:     alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
        Olof Johansson <olof@...om.net>
Subject: [PATCH] ALSA: echoaudio: simplify get_audio_levels

The loop optimizer seems to go astray here, and produces some warnings
that don't seem valid.

Still, the code can be simplified -- just clear the whole array at the
beginning, and fill in whatever values are valid on the platform.

Warnings before this change (GCC 8.2.0 ARM allmodconfig):

In file included from ../sound/pci/echoaudio/gina24.c:115:
../sound/pci/echoaudio/echoaudio.c: In function 'snd_echo_vumeters_get':
../sound/pci/echoaudio/echoaudio_dsp.c:647:9: warning: iteration 1073741824 invokes undefined behavior [-Waggressive-loop-optimizations]
In file included from ../sound/pci/echoaudio/layla24.c:112:
../sound/pci/echoaudio/echoaudio.c: In function 'snd_echo_vumeters_get':
../sound/pci/echoaudio/echoaudio_dsp.c:658:9: warning: iteration 1073741824 invokes undefined behavior [-Waggressive-loop-optimizations]
../sound/pci/echoaudio/echoaudio_dsp.c:647:9: warning: iteration 1073741824 invokes undefined behavior [-Waggressive-loop-optimizations]

Signed-off-by: Olof Johansson <olof@...om.net>
---
 sound/pci/echoaudio/echoaudio_dsp.c | 20 +++++++-------------
 1 file changed, 7 insertions(+), 13 deletions(-)

diff --git a/sound/pci/echoaudio/echoaudio_dsp.c b/sound/pci/echoaudio/echoaudio_dsp.c
index 50d4a87a6bb34..f02f5b1568dee 100644
--- a/sound/pci/echoaudio/echoaudio_dsp.c
+++ b/sound/pci/echoaudio/echoaudio_dsp.c
@@ -635,36 +635,30 @@ This function assumes there are no more than 16 in/out busses or pipes
 Meters is an array [3][16][2] of long. */
 static void get_audio_meters(struct echoaudio *chip, long *meters)
 {
-	int i, m, n;
+	unsigned int i, m, n;
 
-	m = 0;
-	n = 0;
-	for (i = 0; i < num_busses_out(chip); i++, m++) {
+	for (i = 0 ; i < 96; i++)
+		meters[i] = 0;
+
+	for (m = 0, n = 0, i = 0; i < num_busses_out(chip); i++, m++) {
 		meters[n++] = chip->comm_page->vu_meter[m];
 		meters[n++] = chip->comm_page->peak_meter[m];
 	}
-	for (; n < 32; n++)
-		meters[n] = 0;
 
 #ifdef ECHOCARD_ECHO3G
 	m = E3G_MAX_OUTPUTS;	/* Skip unused meters */
 #endif
 
-	for (i = 0; i < num_busses_in(chip); i++, m++) {
+	for (n = 32, i = 0; i < num_busses_in(chip); i++, m++) {
 		meters[n++] = chip->comm_page->vu_meter[m];
 		meters[n++] = chip->comm_page->peak_meter[m];
 	}
-	for (; n < 64; n++)
-		meters[n] = 0;
-
 #ifdef ECHOCARD_HAS_VMIXER
-	for (i = 0; i < num_pipes_out(chip); i++, m++) {
+	for (n = 64, i = 0; i < num_pipes_out(chip); i++, m++) {
 		meters[n++] = chip->comm_page->vu_meter[m];
 		meters[n++] = chip->comm_page->peak_meter[m];
 	}
 #endif
-	for (; n < 96; n++)
-		meters[n] = 0;
 }
 
 
-- 
2.11.0