From e63b97813746e37c95a3ec930fd5763115acf376 Mon Sep 17 00:00:00 2001
From: Paul Gardner-Stephen <paul@servalproject.org>
Date: Wed, 24 Apr 2019 10:32:51 +0930
Subject: [PATCH] ignore many common instruction fragments

---
 src/similarity.c | 22 ++++++++++++++++++++++
 strings/A92020   |  7 +++++++
 2 files changed, 29 insertions(+)
 create mode 100644 strings/A92020

diff --git a/src/similarity.c b/src/similarity.c
index 0d5e9581..9bb9fe98 100644
--- a/src/similarity.c
+++ b/src/similarity.c
@@ -100,6 +100,28 @@ int main(int argc,char **argv)
 	// since that is the max length of a 6502 instruction
 	int single_instruction=0;
 	if (k==3) {
+	  // Reject some very common instruction fragments
+
+
+	  // Branch followed by any opcode
+	  if (f1[i]==0xd0) break;
+	  if (f1[i]==0xf0) break;
+	  if (f1[i]==0xb0) break;
+	  if (f1[i]==0x10) break;
+
+	  if (f1[i+1]==0x85) {
+	    // Single byte followed by STA $xx
+	    // Super common, so can be ignored.
+	    break;
+	  }
+
+	  // Common 2-byte instructions followed by
+	  // any single byte are very common and not
+	  // copyrightable.
+	  if (f1[i]==0x85) break;
+	  if (f1[i]==0xa9) break;
+	  if (f1[i]==0xc9) break;
+	  
 	  // Filter out all 3 byte instructions
 	  switch(f1[i]) {
 	  case 0x0C: //   TSB $nnnn
diff --git a/strings/A92020 b/strings/A92020
new file mode 100644
index 00000000..b317f90a
--- /dev/null
+++ b/strings/A92020
@@ -0,0 +1,7 @@
+LDA #$20, then call a routine
+
+LDA #$20
+JSR $xxxx
+
+Obvious sequence for doing this.
+Not copyrightable.