From c13696aca1ccce8a33f5cf6d27598776054f08a0 Mon Sep 17 00:00:00 2001
From: Wim Taymans <wtaymans@redhat.com>
Date: Fri, 30 Jun 2023 17:49:29 +0200
Subject: [PATCH] filter-chain: simplify biquads

---
 spa/plugins/audioconvert/crossover.c        | 48 +++++++++------------
 src/modules/module-filter-chain/dsp-ops-c.c | 16 +++----
 2 files changed, 26 insertions(+), 38 deletions(-)

diff --git a/spa/plugins/audioconvert/crossover.c b/spa/plugins/audioconvert/crossover.c
index 7575833cd..177cf6106 100644
--- a/spa/plugins/audioconvert/crossover.c
+++ b/spa/plugins/audioconvert/crossover.c
@@ -22,17 +22,16 @@ void lr4_set(struct lr4 *lr4, enum biquad_type type, float freq)
 
 void lr4_process(struct lr4 *lr4, float *dst, const float *src, const float vol, int samples)
 {
-	float lx1 = lr4->x1;
-	float lx2 = lr4->x2;
-	float ly1 = lr4->y1;
-	float ly2 = lr4->y2;
-	float lz1 = lr4->z1;
-	float lz2 = lr4->z2;
-	float lb0 = lr4->bq.b0;
-	float lb1 = lr4->bq.b1;
-	float lb2 = lr4->bq.b2;
-	float la1 = lr4->bq.a1;
-	float la2 = lr4->bq.a2;
+	float x1 = lr4->x1;
+	float x2 = lr4->x2;
+	float y1 = lr4->y1;
+	float y2 = lr4->y2;
+	float b0 = lr4->bq.b0;
+	float b1 = lr4->bq.b1;
+	float b2 = lr4->bq.b2;
+	float a1 = lr4->bq.a1;
+	float a2 = lr4->bq.a2;
+	float x, y, z;
 	int i;
 
 	if (vol == 0.0f) {
@@ -47,24 +46,19 @@ void lr4_process(struct lr4 *lr4, float *dst, const float *src, const float vol,
 	}
 
 	for (i = 0; i < samples; i++) {
-		float x, y, z;
-		x = src[i];
-		y = lb0*x + lb1*lx1 + lb2*lx2 - la1*ly1 - la2*ly2;
-		z = lb0*y + lb1*ly1 + lb2*ly2 - la1*lz1 - la2*lz2;
-		lx2 = lx1;
-		lx1 = x;
-		ly2 = ly1;
-		ly1 = y;
-		lz2 = lz1;
-		lz1 = z;
+		x  = src[i];
+		y  = b0 * x          + x1;
+		x1 = b1 * x - a1 * y + x2;
+		x2 = b2 * x - a2 * y;
+		z  = b0 * y          + y1;
+		y1 = b1 * y - a1 * z + y2;
+		y2 = b2 * y - a2 * z;
 		dst[i] = z * vol;
 	}
 #define F(x) (-FLT_MIN < (x) && (x) < FLT_MIN ? 0.0f : (x))
-	lr4->x1 = F(lx1);
-	lr4->x2 = F(lx2);
-	lr4->y1 = F(ly1);
-	lr4->y2 = F(ly2);
-	lr4->z1 = F(lz1);
-	lr4->z2 = F(lz2);
+	lr4->x1 = F(x1);
+	lr4->x2 = F(x2);
+	lr4->y1 = F(y1);
+	lr4->y2 = F(y2);
 #undef F
 }
diff --git a/src/modules/module-filter-chain/dsp-ops-c.c b/src/modules/module-filter-chain/dsp-ops-c.c
index fb5d1cdd5..68b3080e8 100644
--- a/src/modules/module-filter-chain/dsp-ops-c.c
+++ b/src/modules/module-filter-chain/dsp-ops-c.c
@@ -84,33 +84,27 @@ void dsp_mix_gain_c(struct dsp_ops *ops,
 void dsp_biquad_run_c(struct dsp_ops *ops, struct biquad *bq,
 		float *out, const float *in, uint32_t n_samples)
 {
-	float x1, x2, y1, y2;
+	float x, y, x1, x2;
 	float b0, b1, b2, a1, a2;
 	uint32_t i;
 
 	x1 = bq->x1;
 	x2 = bq->x2;
-	y1 = bq->y1;
-	y2 = bq->y2;
 	b0 = bq->b0;
 	b1 = bq->b1;
 	b2 = bq->b2;
 	a1 = bq->a1;
 	a2 = bq->a2;
 	for (i = 0; i < n_samples; i++) {
-		float x = in[i];
-		float y = b0 * x + b1 * x1 + b2 * x2 - a1 * y1 - a2 * y2;
+		x  = in[i];
+		y  = b0 * x          + x1;
+		x1 = b1 * x - a1 * y + x2;
+		x2 = b2 * x - a2 * y;
 		out[i] = y;
-		x2 = x1;
-		x1 = x;
-		y2 = y1;
-		y1 = y;
 	}
 #define F(x) (-FLT_MIN < (x) && (x) < FLT_MIN ? 0.0f : (x))
 	bq->x1 = F(x1);
 	bq->x2 = F(x2);
-	bq->y1 = F(y1);
-	bq->y2 = F(y2);
 #undef F
 }