From c53c7bfd1d244cfab8aea62815dd577f0bcaf864 Mon Sep 17 00:00:00 2001
From: Peter Evans <peter@modul8r.com>
Date: Sat, 21 Apr 2018 23:15:48 -0500
Subject: [PATCH] Add function to return true if an instruction would write to
 memory

---
 include/mos6502/mos6502.h |  1 +
 src/mos6502/mos6502.c     | 16 ++++++++++++++++
 2 files changed, 17 insertions(+)

diff --git a/include/mos6502/mos6502.h b/include/mos6502/mos6502.h
index ccb9930..dfb4442 100644
--- a/include/mos6502/mos6502.h
+++ b/include/mos6502/mos6502.h
@@ -166,6 +166,7 @@ typedef vm_8bit (*mos6502_address_resolver)(mos6502 *);
 typedef void (*mos6502_instruction_handler)(mos6502 *, vm_8bit);
 
 extern bool mos6502_would_jump(int);
+extern bool mos6502_would_write_mem(int);
 extern int mos6502_cycles(mos6502 *, vm_8bit);
 extern int mos6502_instruction(vm_8bit);
 extern mos6502 *mos6502_create(vm_segment *, vm_segment *);
diff --git a/src/mos6502/mos6502.c b/src/mos6502/mos6502.c
index b1a5c28..644b307 100644
--- a/src/mos6502/mos6502.c
+++ b/src/mos6502/mos6502.c
@@ -404,6 +404,22 @@ mos6502_would_jump(int inst_code)
         inst_code == RTI;
 }
 
+/*
+ * Return true if the given instruction _might_ write to memory, if used
+ * with an appropriate address mode (e.g. anything other than ACC).
+ */
+inline bool
+mos6502_would_write_mem(int inst_code)
+{
+    return
+        inst_code == ASL ||
+        inst_code == DEC ||
+        inst_code == INC ||
+        inst_code == LSR ||
+        inst_code == ROL ||
+        inst_code == ROR;
+}
+
 /*
  * This is a _kind_ of factory method, except we're obviously not
  * instantiating an object. Given an address mode, we return the