From b7e26002be728ae5eeebffcb336a4d5f4db2a719 Mon Sep 17 00:00:00 2001
From: Wim Taymans <wtaymans@redhat.com>
Date: Tue, 28 Jun 2022 10:11:46 +0200
Subject: [PATCH] audiocovert: improve dither setup

The quantize is the amount of bits we want to keep from the original
signal, subtract the amount of bits for noise. Clamp this to 0 (all
noise).
Calculate the scale factor better with powf() and avoid overflows.

Fixes #2479
---
 spa/plugins/audioconvert/audioconvert.c | 7 ++++---
 spa/plugins/audioconvert/dither-ops.c   | 5 +----
 spa/plugins/audioconvert/dither-ops.h   | 8 ++++----
 3 files changed, 9 insertions(+), 11 deletions(-)

diff --git a/spa/plugins/audioconvert/audioconvert.c b/spa/plugins/audioconvert/audioconvert.c
index 6673a8b46..4fd17a071 100644
--- a/spa/plugins/audioconvert/audioconvert.c
+++ b/spa/plugins/audioconvert/audioconvert.c
@@ -1395,9 +1395,10 @@ static int setup_out_convert(struct impl *this)
 	spa_log_debug(this->log, "%p: got converter features %08x:%08x passthrough:%d", this,
 			this->cpu_flags, out->conv.cpu_flags, out->conv.is_passthrough);
 
+
 	if (this->props.dither_noise > 0) {
-		this->dither.quantize = 32 - (calc_width(&dst_info) * 8);
-		this->dither.quantize += this->props.dither_noise;
+		this->dither.quantize = calc_width(&dst_info) * 8;
+		this->dither.quantize -= SPA_MIN(this->dither.quantize, this->props.dither_noise);
 		this->dither.n_channels = dst_info.info.raw.channels;
 		this->dither.cpu_flags = this->cpu_flags;
 
@@ -2478,7 +2479,7 @@ static int impl_node_process(void *object)
 	}
 	this->out_offset += n_samples;
 
-	if (this->props.dither_noise > 0) {
+	if (this->dither.process != NULL) {
 		in_datas = (const void**)out_datas;
 		if (out_passthrough)
 			out_datas = dst_datas;
diff --git a/spa/plugins/audioconvert/dither-ops.c b/spa/plugins/audioconvert/dither-ops.c
index ffb79989c..ee9d039c9 100644
--- a/spa/plugins/audioconvert/dither-ops.c
+++ b/spa/plugins/audioconvert/dither-ops.c
@@ -79,10 +79,7 @@ int dither_init(struct dither *d)
 	if (info == NULL)
 		return -ENOTSUP;
 
-	if (d->quantize >= 32)
-		return -EINVAL;
-
-	d->scale = 1.0f / (1ULL << (63 - d->quantize));
+	d->scale = 1.0f / powf(2.0f, 31 + d->quantize);
 
 	d->dither_size = DITHER_SIZE;
 	d->dither = calloc(d->dither_size + DITHER_OPS_MAX_OVERREAD +
diff --git a/spa/plugins/audioconvert/dither-ops.h b/spa/plugins/audioconvert/dither-ops.h
index afa96db5f..7f0f9bc60 100644
--- a/spa/plugins/audioconvert/dither-ops.h
+++ b/spa/plugins/audioconvert/dither-ops.h
@@ -34,10 +34,10 @@
 
 struct dither {
 	uint32_t quantize;
-#define DITHER_METHOD_NONE 		0
-#define DITHER_METHOD_RECTANGULAR 	2
-#define DITHER_METHOD_TRIANGULAR 	3
-#define DITHER_METHOD_SHAPED_5	 	4
+#define DITHER_METHOD_NONE		0
+#define DITHER_METHOD_RECTANGULAR	2
+#define DITHER_METHOD_TRIANGULAR	3
+#define DITHER_METHOD_SHAPED_5		4
 	uint32_t method;
 	uint32_t n_channels;
 	uint32_t cpu_flags;