From ddfdeffc99eddde9c447d00dac9727dc010f0f49 Mon Sep 17 00:00:00 2001
From: tildearrow <tildearrow@protonmail.com>
Date: Sat, 24 Sep 2022 16:44:47 -0500
Subject: [PATCH] update brrUtils (again)

---
 src/engine/brrUtils.c | 80 +++++++++++++++++++++++++++++++++++++++++--
 src/engine/brrUtils.h |  3 +-
 2 files changed, 79 insertions(+), 4 deletions(-)

diff --git a/src/engine/brrUtils.c b/src/engine/brrUtils.c
index 123ec165d..a32e51603 100644
--- a/src/engine/brrUtils.c
+++ b/src/engine/brrUtils.c
@@ -22,10 +22,81 @@
 
 #include "brrUtils.h"
 
-long brrEncode(short* buf, unsigned char* out, long len) {
+long brrEncode(short* buf, unsigned char* out, long len, long loopStart) {
   if (len==0) return 0;
-  // TODO
-  return 0;
+
+  // encoding process:
+  // 1. read next group of 16 samples
+  // 2. is this the first block?
+  //    - if yes, don't filter. output and then go to 1
+  // 3. is this the loop block?
+  //    - if yes, don't filter. output and then go to 1
+  // 4. try encoding using 4 filters
+  // 5. which one of these yields the least amount of error?
+  // 6. output the one which does
+  // 7. is this the last block?
+  //    - if yes, mark end and finish
+  // 8. go to 1
+  long total=0;
+  unsigned char next[9];
+  unsigned char filter=0;
+  unsigned char range=0;
+  unsigned char o=0;
+  short o0=0;
+
+  len&=~15;
+  loopStart&=~15;
+  for (long i=0; i<len; i+=16) {
+    // don't filter on the first or loop block
+    if (i && i!=loopStart) {
+
+    } else {
+      filter=0;
+    }
+
+    range=0;
+    for (int j=0; j<16; j++) {
+      short s=buf[j];
+      if (s<0) s=-s;
+      while (range<11 && s>((8<<range)-1)) range++;
+    }
+    next[0]=(range<<4)|(filter<<2)|((i+16>len)?1:0);
+    switch (filter) {
+      case 0:
+        for (int j=0; j<16; j++) {
+          o0=buf[j]>>range;
+          if (o0>7) o0=7;
+          if (o0<-8) o0=-8;
+          o=o0&15;
+          if (j&1) {
+            next[1+(j>>1)]|=o;
+          } else {
+            next[1+(j>>1)]=o<<4;
+          }
+        }
+        break;
+      case 1:
+        break;
+      case 2:
+        break;
+      case 3:
+        break;
+    }
+
+    out[0]=next[0];
+    out[1]=next[1];
+    out[2]=next[2];
+    out[3]=next[3];
+    out[4]=next[4];
+    out[5]=next[5];
+    out[6]=next[6];
+    out[7]=next[7];
+    out[8]=next[8];
+    buf+=16;
+    out+=9;
+    total+=9;
+  }
+  return total;
 }
 
 #define DO_ONE_SAMPLE \
@@ -55,6 +126,9 @@ long brrEncode(short* buf, unsigned char* out, long len) {
   *out=next; \
   out++;
 
+// TODO:
+// - what happens during overflow?
+// - what happens when range values 12 to 15 are used?
 long brrDecode(unsigned char* buf, short* out, long len) {
   if (len==0) return 0;
 
diff --git a/src/engine/brrUtils.h b/src/engine/brrUtils.h
index ba3a6f534..4ada8b1e3 100644
--- a/src/engine/brrUtils.h
+++ b/src/engine/brrUtils.h
@@ -32,9 +32,10 @@ extern "C" {
  * @param buf input data.
  * @param out output buffer. shall be at least 9*(len/16) shorts in size.
  * @param len input length (should be a multiple of 16. if it isn't, the output will be padded).
+ * @param loopStart beginning of loop area (may be 0 for no loop). this is used to ensure the respective block has no filter in order to loop properly.
  * @return number of written samples.
  */
-long brrEncode(short* buf, unsigned char* out, long len);
+long brrEncode(short* buf, unsigned char* out, long len, long loopStart);
 
 /**
  * read len bytes from buf, decode BRR and output to out.