From 0a39fd12370e66df0253d19460850cc3cc158b7f Mon Sep 17 00:00:00 2001
From: Mikael Pettersson <mikpelinux@gmail.com>
Date: Tue, 16 Jul 2013 16:52:22 +0000
Subject: [PATCH] pdp10-opcodes: add pdp10_instruction_from_high13() helper for
 decoding/disassembly

---
 include/pdp10-opcodes.h |  2 ++
 lib/pdp10-opcodes.c     | 26 ++++++++++++++++++++++++++
 2 files changed, 28 insertions(+)

diff --git a/include/pdp10-opcodes.h b/include/pdp10-opcodes.h
index 9097076..b51b8b8 100644
--- a/include/pdp10-opcodes.h
+++ b/include/pdp10-opcodes.h
@@ -130,4 +130,6 @@ extern const unsigned int pdp10_num_aliases;
 extern const struct pdp10_instruction pdp10_extended_instruction[];
 extern const unsigned int pdp10_num_extended_instructions;
 
+const struct pdp10_instruction *pdp10_instruction_from_high13(unsigned int high13);
+
 #endif /* PDP10_OPCODES_H */
diff --git a/lib/pdp10-opcodes.c b/lib/pdp10-opcodes.c
index 311af37..76128b2 100644
--- a/lib/pdp10-opcodes.c
+++ b/lib/pdp10-opcodes.c
@@ -957,3 +957,29 @@ const struct pdp10_instruction pdp10_extended_instruction[] =
 
 const unsigned int pdp10_num_extended_instructions =
     sizeof pdp10_extended_instruction / sizeof pdp10_extended_instruction[0];
+
+static int pdp10_opcode_matches(unsigned int high13, const struct pdp10_instruction *insn)
+{
+    unsigned int opcode;
+
+    if ((insn->type & PDP10_A_OPCODE) || (insn->type & PDP10_IO))
+	opcode = high13 << 2;	/* table entry has 5 octal digits == 15 bits */
+    else
+	opcode = high13 >> 4;	/* table entry has 3 octal digits == 9 bits */
+    return opcode == insn->opcode;
+}
+
+const struct pdp10_instruction *pdp10_instruction_from_high13(unsigned int high13)
+{
+    unsigned int i;
+
+    for (i = 0; i < pdp10_num_aliases; ++i)
+	if (pdp10_opcode_matches(high13, &pdp10_alias[i]))
+	    return &pdp10_alias[i];
+
+    for (i = 0; i < pdp10_num_instructions; ++i)
+	if (pdp10_opcode_matches(high13, &pdp10_instruction[i]))
+	    return &pdp10_instruction[i];
+
+    return (void*)0;
+}