From c0d38d941a1c6acf246b1ee8c4d4b0b1e9dd0b69 Mon Sep 17 00:00:00 2001
From: Max Kellermann <max.kellermann@gmail.com>
Date: Mon, 13 Mar 2023 13:31:46 +0100
Subject: [PATCH] pcm/Normalizer: split the normalization loop

Performance improvement because the ramp code is now moved out of the
hot code path, allowing the compiler to vectorize.
---
 src/pcm/Normalizer.cxx | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/src/pcm/Normalizer.cxx b/src/pcm/Normalizer.cxx
index 164d0fef9..982e52a69 100644
--- a/src/pcm/Normalizer.cxx
+++ b/src/pcm/Normalizer.cxx
@@ -71,15 +71,19 @@ PcmNormalizer::ProcessS16(int16_t *gcc_restrict dest,
                 curGain = 1 << 10;
 	const int delta = (newGain - curGain) / (int)ramp;
 
-	for (std::size_t i = 0; i < src.size(); i++) {
+	for (const auto sample : src.first(ramp)) {
 		//! Amplify the sample
-		*dest++ = PcmClamp<format>(src[i] * curGain >> 10);
+		*dest++ = PcmClamp<format>(sample * curGain >> 10);
 
                 //! Adjust the gain
-                if (i < ramp)
-                        curGain += delta;
-                else
-                        curGain = newGain;
+		curGain += delta;
+	}
+
+	curGain = newGain;
+
+	for (const auto sample : src.subspan(ramp)) {
+		//! Amplify the sample
+		*dest++ = PcmClamp<format>(sample * curGain >> 10);
 	}
 
         pos = slot;