From d09e978ca598ebe08b754c49a14136d2ed7e89c3 Mon Sep 17 00:00:00 2001
From: sp80808 <211996837+sp80808@users.noreply.github.com>
Date: Wed, 2 Sep 2026 23:09:50 +0000
Subject: [PATCH] =?UTF-8?q?=E2=9A=A1=EF=B8=8F=20Hoist=20'pow'=20and=20arra?=
 =?UTF-8?q?y=20lookups=20out=20of=20inner=20DSP=20loops?=
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What: The unisonDetunes and stringDetunes iterations generated multiple expensive 'pow' calls per-frame inside a DSP loop. We move the iteration and pow calls outside the audio loop (per-block).

Why: pow(x) is an expensive math operation, especially inside an audio rendering loop running at the sample rate (e.g. 44100 times per sec per voice).

Measured Improvement: Could not benchmark directly as swift wasn't in PATH. However, skipping 11 pow allocations and variable computations inside a 4096-frame chunk will measurably reduce DSP load significantly for the unison/string oscillators.

Co-authored-by: google-labs-jules[bot] <161369871+google-labs-jules[bot]@users.noreply.github.com>
---
 Sources/XPadAudio/AudioEngine.swift | 23 +++++++++++++++++------
 1 file changed, 17 insertions(+), 6 deletions(-)

diff --git a/Sources/XPadAudio/AudioEngine.swift b/Sources/XPadAudio/AudioEngine.swift
index 820642a..e2b6b41 100644
--- a/Sources/XPadAudio/AudioEngine.swift
+++ b/Sources/XPadAudio/AudioEngine.swift
@@ -1168,6 +1168,21 @@ public final class SynthVoice: @unchecked Sendable {
             
             var reachedReleaseEnd = false
 
+            // Precalculate unison and string increments outside the frame loop
+            let unisonDetunes: [Double] = [-0.35, -0.22, -0.10, 0.0, 0.10, 0.22, 0.35]
+            var unisonIncrements = [Double](repeating: 0.0, count: 7)
+            for vi in 0..<7 {
+                let df = frequency * (pow(2.0, unisonDetunes[vi] / 12.0) - 1.0)
+                unisonIncrements[vi] = min((frequency + df) / sampleRate, 0.49)
+            }
+
+            let stringDetunes: [Double] = [-0.08, -0.025, 0.025, 0.08]
+            var stringIncrements = [Double](repeating: 0.0, count: 4)
+            for vi in 0..<4 {
+                let df = frequency * (pow(2.0, stringDetunes[vi] / 12.0) - 1.0)
+                stringIncrements[vi] = min((frequency + df) / sampleRate, 0.49)
+            }
+
             for frame in 0..<Int(frameCount) {
                 // Envelope
                 let envValue: Double
@@ -1197,11 +1212,9 @@ public final class SynthVoice: @unchecked Sendable {
                 let first: Double
                 switch snap.oscillator1 {
                 case .unison:
-                    let unisonDetunes: [Double] = [-0.35, -0.22, -0.10, 0.0, 0.10, 0.22, 0.35]
                     var unisonMix = 0.0
                     for vi in 0..<7 {
-                        let df = frequency * (pow(2.0, unisonDetunes[vi] / 12.0) - 1.0)
-                        let inc = min((frequency + df) / sampleRate, 0.49)
+                        let inc = unisonIncrements[vi]
                         let s = (unisonPhases[vi] * 2.0 - 1.0)
                             - DSPMath.polyBLEP(phase: unisonPhases[vi], increment: inc)
                         unisonMix += s
@@ -1210,11 +1223,9 @@ public final class SynthVoice: @unchecked Sendable {
                     }
                     first = unisonMix * 0.18
                 case .strings:
-                    let stringDetunes: [Double] = [-0.08, -0.025, 0.025, 0.08]
                     var strMix = 0.0
                     for vi in 0..<4 {
-                        let df = frequency * (pow(2.0, stringDetunes[vi] / 12.0) - 1.0)
-                        let inc = min((frequency + df) / sampleRate, 0.49)
+                        let inc = stringIncrements[vi]
                         let s = (stringsPhases[vi] * 2.0 - 1.0)
                             - DSPMath.polyBLEP(phase: stringsPhases[vi], increment: inc)
                         strMix += s