From a18506bada9df6a528301a8eacab6082e91a7127 Mon Sep 17 00:00:00 2001
From: Bad Diode <bd@badd10de.dev>
Date: Wed, 26 May 2021 15:21:48 +0200
Subject: [WIP] Speed up the mixer

---
 src/uxn/devices/apu.c | 43 +++++++++++++++++++++++++++----------------
 1 file changed, 27 insertions(+), 16 deletions(-)

diff --git a/src/uxn/devices/apu.c b/src/uxn/devices/apu.c
index ba9fe88..c3168c2 100644
--- a/src/uxn/devices/apu.c
+++ b/src/uxn/devices/apu.c
@@ -202,29 +202,40 @@ void sound_mix() {
         if (chan->data == NULL) {
             continue;
         }
-        for(size_t i = 0; i < AUDIO_BUF_LEN; i++) {
-            // Remember we are using fixed point values.
-            mix_buffer[i] += chan->data[chan->pos >> 12] * chan->vol;
-            chan->pos += chan->inc;
-
-            if (chan->pos >= chan->length) {
-                // If looping is not active disable the channel.
-                if (chan->loop_length == 0) {
-                    chan->data = NULL;
-                    break;
-                }
-
-                // Loop the sample.
-                while (chan->pos >= chan->length) {
-                    chan->pos -= chan->loop_length;
+        if (chan->pos + chan->inc * AUDIO_BUF_LEN >= chan->length) {
+            // Sample is going to finish, need to consider this for looping or
+            // stopping.
+            for(size_t i = 0; i < AUDIO_BUF_LEN; i++) {
+                // Remember we are using fixed point values.
+                mix_buffer[i] += chan->data[chan->pos >> 12] * chan->vol;
+                chan->pos += chan->inc;
+
+                if (chan->pos >= chan->length) {
+                    // If looping is not active disable the channel.
+                    if (chan->loop_length == 0) {
+                        chan->data = NULL;
+                        break;
+                    }
+
+                    // Loop the sample.
+                    while (chan->pos >= chan->length) {
+                        chan->pos -= chan->loop_length;
+                    }
                 }
             }
+        } else {
+            // Sample still have room to go, no need to check for looping or
+            // end of sample.
+            for(size_t i = 0; i < AUDIO_BUF_LEN; i++) {
+                mix_buffer[i] += chan->data[chan->pos>>12] * chan->vol;
+                chan->pos += chan->inc;
+            }
         }
     }
 
     // Downsample and copy to the playing buffer.
     for (size_t i = 0; i < AUDIO_BUF_LEN; ++i) {
-        // >> 8 to divide off the volume, >> 2 to divide by 4 channels to
+        // >> 6 to divide off the volume, >> 2 to divide by 4 channels to
         // prevent overflow.
         audio.current_buffer[i] = mix_buffer[i] >> 8;
     }
-- 
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