From 909963506109d475732feeff367e5e2a74974344 Mon Sep 17 00:00:00 2001
From: aliaspider
Date: Mon, 9 Nov 2015 21:17:01 +0100
Subject: add sound interpolation

---
 libretro/libretro.c |  2 ++
 src/soundux.c       | 40 +++++++++++++++++++++++++++++++++++++++-
 2 files changed, 41 insertions(+), 1 deletion(-)

diff --git a/libretro/libretro.c b/libretro/libretro.c
index c1665b4..b7aa69b 100644
--- a/libretro/libretro.c
+++ b/libretro/libretro.c
@@ -252,6 +252,8 @@ static void snes_init (void)
 	Settings.SpeedHacks = TRUE;
 
 	Settings.HBlankStart = (256 * Settings.H_Max) / SNES_HCOUNTER_MAX;
+
+   Settings.InterpolatedSound = TRUE;
    /*
    	Settings.SoundPlaybackRate = 5;
     Settings.Stereo = TRUE;
diff --git a/src/soundux.c b/src/soundux.c
index 60d5540..67f7127 100644
--- a/src/soundux.c
+++ b/src/soundux.c
@@ -187,6 +187,7 @@ void S9xFixSoundAfterSnapshotLoad()
       S9xSetSoundFrequency(i, SoundData.channels[i].hertz);
       SoundData.channels [i].envxx = SoundData.channels [i].envx << ENVX_SHIFT;
       SoundData.channels [i].next_sample = 0;
+      SoundData.channels [i].interpolate = 0;
       SoundData.channels [i].previous [0] = (int32) SoundData.channels [i].previous16 [0];
       SoundData.channels [i].previous [1] = (int32) SoundData.channels [i].previous16 [1];
    }
@@ -380,6 +381,11 @@ static void MixStereo(int sample_count)
             ch->sample_pointer = SOUND_DECODE_LENGTH - 1;
 
          ch->next_sample = ch->block[ch->sample_pointer];
+         ch->interpolate = 0;
+
+         if (Settings.InterpolatedSound && freq0 < FIXED_POINT && !mod)
+            ch->interpolate = ((ch->next_sample - ch->sample) *
+                               (long) freq0) / (long) FIXED_POINT;
       }
       VL = (ch->sample * ch-> left_vol_level) / 128;
       VR = (ch->sample * ch->right_vol_level) / 128;
@@ -587,17 +593,49 @@ static void MixStereo(int sample_count)
             else
                ch->next_sample = ch->block [ch->sample_pointer];
 
-            if (ch->type != SOUND_SAMPLE)
+            if (ch->type == SOUND_SAMPLE)
             {
+               if (Settings.InterpolatedSound && freq < FIXED_POINT && !mod)
+               {
+                  ch->interpolate = ((ch->next_sample - ch->sample) *
+                                     (long) freq) / (long) FIXED_POINT;
+                  ch->sample = (int16_t)(ch->sample + (((ch->next_sample - ch->sample) *
+                                                      (long)(ch->count)) / (long) FIXED_POINT));
+               }
+               else
+                  ch->interpolate = 0;
+            }
+            else
+            {
+#if 1
+               // Snes9x 1.53's SPC_DSP.cpp, by blargg
+               int feedback = (so.noise_gen << 13) ^ (so.noise_gen << 14);
+               so.noise_gen = (feedback & 0x4000) ^ (so.noise_gen >> 1);
+               ch->sample = (so.noise_gen << 17) >> 17;
+               ch->interpolate = 0;
+#else
                for (; VL > 0; VL--)
                   if ((so.noise_gen <<= 1) & 0x80000000L)
                      so.noise_gen ^= 0x0040001L;
                ch->sample = (so.noise_gen << 17) >> 17;
+#endif
             }
 
             VL = (ch->sample * ch-> left_vol_level) / 128;
             VR = (ch->sample * ch->right_vol_level) / 128;
          }
+         else
+         {
+            if (ch->interpolate)
+            {
+               int32_t s = (int32_t) ch->sample + ch->interpolate;
+
+               CLIP16(s);
+               ch->sample = (int16_t) s;
+               VL = (ch->sample * ch-> left_vol_level) / 128;
+               VR = (ch->sample * ch->right_vol_level) / 128;
+            }
+         }
 
          if (pitch_mod & (1 << (J + 1)))
             wave [I / 2] = ch->sample * ch->envx;
-- 
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