From 69f27e744180fd95f3e2461d34a11a55ca76a003 Mon Sep 17 00:00:00 2001
From: Jean Pierre Cimalando <jp-dev@inbox.ru>
Date: Thu, 18 Mar 2021 13:52:14 +0100
Subject: [PATCH 1/2] Linear smoother: ensure to get the derivative correct

---
 src/sfizz/Smoothers.cpp | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/src/sfizz/Smoothers.cpp b/src/sfizz/Smoothers.cpp
index 9dcd8023..dff32e78 100644
--- a/src/sfizz/Smoothers.cpp
+++ b/src/sfizz/Smoothers.cpp
@@ -101,8 +101,8 @@ void LinearSmoother::process(absl::Span<const float> input, absl::Span<float> ou
         if (target != nextTarget) {
             target = nextTarget;
             //framesToTarget = (framesToTarget > 0) ? framesToTarget : smoothFrames;
-            //step = (target - current) / max(1, framesToTarget);
-            step = (target - current) / max(1, smoothFrames);
+            //step = (target - current) / (16 * max(1, framesToTarget));
+            step = (target - current) / (16 * max(1, smoothFrames));
         }
         const simde__m128 targetX4 = simde_mm_set1_ps(target);
         if (target > current) {
@@ -149,8 +149,8 @@ void LinearSmoother::process(absl::Span<const float> input, absl::Span<float> ou
         if (target != nextTarget) {
             target = nextTarget;
             // framesToTarget = (framesToTarget > 0) ? framesToTarget : smoothFrames;
-            // step = (target - current) / max(1, framesToTarget);
-            step = (target - current) / max(1, smoothFrames);
+            // step = (target - current) / ((count - i) * max(1, framesToTarget));
+            step = (target - current) / ((count - i) * max(1, smoothFrames));
         }
         if (target > current) {
             for (; i < count; ++i)

From 3f5f4ef2c4d37e786df9c4d7bd7ce9d44a0976fb Mon Sep 17 00:00:00 2001
From: Jean Pierre Cimalando <jp-dev@inbox.ru>
Date: Thu, 18 Mar 2021 13:54:23 +0100
Subject: [PATCH 2/2] Add the non-SIMD linear smoother (for reference)

---
 src/sfizz/Smoothers.cpp | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/src/sfizz/Smoothers.cpp b/src/sfizz/Smoothers.cpp
index dff32e78..970c05bb 100644
--- a/src/sfizz/Smoothers.cpp
+++ b/src/sfizz/Smoothers.cpp
@@ -9,7 +9,10 @@
 #include "MathHelpers.h"
 #include "SfzHelpers.h"
 #include "SIMDHelpers.h"
+#include <simde/simde-features.h>
+#if SIMDE_NATURAL_VECTOR_SIZE_GE(128)
 #include <simde/x86/sse.h>
+#endif
 
 namespace sfz {
 
@@ -96,6 +99,7 @@ void LinearSmoother::process(absl::Span<const float> input, absl::Span<float> ou
     // int32_t framesToTarget = framesToTarget_;
     const int32_t smoothFrames = smoothFrames_;
 
+#if SIMDE_NATURAL_VECTOR_SIZE_GE(128)
     for (; i + 15 < count; i += 16) {
         const float nextTarget = input[i + 15];
         if (target != nextTarget) {
@@ -143,6 +147,32 @@ void LinearSmoother::process(absl::Span<const float> input, absl::Span<float> ou
         }
         //framesToTarget -= 16;
     }
+#else
+    for (; i + 15 < count; i += 16) {
+        const float nextTarget = input[i + 15];
+
+        if (target != nextTarget) {
+            target = nextTarget;
+            //framesToTarget = (framesToTarget > 0) ? framesToTarget : smoothFrames;
+            //step = (target - current) / (16 * max(1, framesToTarget));
+            step = (target - current) / (16 * max(1, smoothFrames));
+        }
+        if (target > current) {
+            for (size_t j = 0; j < 16; ++j)
+                output[i + j] = current = min(target, current + step);
+        }
+        else if (target < current) {
+            for (size_t j = 0; j < 16; ++j)
+                output[i + j] = current = max(target, current + step);
+        }
+        else {
+            for (size_t j = 0; j < 16; ++j)
+                output[i + j] = target;
+        }
+
+        //framesToTarget -= 16;
+    }
+#endif
 
     if (i < count) {
         const float nextTarget = input[count - 1];