StreamADPCM: Turn the ADPCM decoder into a class

Migrates the state to be instance-based as opposed to being a flat
namespace. This keeps behavior localized to its own instantiable unit
(and forces uses of the class to also be localized, lest they cart around
an instance all over the place).

Source/Core/Core/HW/StreamADPCM.cpp

@@ -12,12 +12,6 @@
 
 namespace StreamADPCM
 {
-// STATE_TO_SAVE
-static s32 histl1;
-static s32 histl2;
-static s32 histr1;
-static s32 histr2;
-
 static s16 ADPDecodeSample(s32 bits, s32 q, s32& hist1, s32& hist2)
 {
   s32 hist = 0;
@@ -49,30 +43,30 @@ static s16 ADPDecodeSample(s32 bits, s32 q, s32& hist1, s32& hist2)
   return (s16)cur;
 }
 
-void InitFilter()
+void ADPCMDecoder::ResetFilter()
 {
-  histl1 = 0;
-  histl2 = 0;
-  histr1 = 0;
-  histr2 = 0;
+  m_histl1 = 0;
+  m_histl2 = 0;
+  m_histr1 = 0;
+  m_histr2 = 0;
 }
 
-void DoState(PointerWrap& p)
+void ADPCMDecoder::DoState(PointerWrap& p)
 {
-  p.Do(histl1);
-  p.Do(histl2);
-  p.Do(histr1);
-  p.Do(histr2);
+  p.Do(m_histl1);
+  p.Do(m_histl2);
+  p.Do(m_histr1);
+  p.Do(m_histr2);
 }
 
-void DecodeBlock(s16* pcm, const u8* adpcm)
+void ADPCMDecoder::DecodeBlock(s16* pcm, const u8* adpcm)
 {
   for (int i = 0; i < SAMPLES_PER_BLOCK; i++)
   {
     pcm[i * 2] = ADPDecodeSample(adpcm[i + (ONE_BLOCK_SIZE - SAMPLES_PER_BLOCK)] & 0xf, adpcm[0],
-                                 histl1, histl2);
+                                 m_histl1, m_histl2);
     pcm[i * 2 + 1] = ADPDecodeSample(adpcm[i + (ONE_BLOCK_SIZE - SAMPLES_PER_BLOCK)] >> 4, adpcm[1],
-                                     histr1, histr2);
+                                     m_histr1, m_histr2);
   }
 }
 }