From fc62d0c9e72cbe22bfdb803bffa2cd4df41a77d0 Mon Sep 17 00:00:00 2001
From: Kelvin Sherlock <ksherlock@gmail.com>
Date: Tue, 31 Aug 2021 18:08:08 -0400
Subject: [PATCH] 'a' as an operand is ignored.

Based on testing with Merlin-16+ 4.12, this seems to apply in all cases

inc a -> equivalent to inc
lda a -> equivalent to lda (bad address mode error)

if you do have an 'a' label, you need to specify the address mode, eg

lda |a, lda >a, lda <a
---
 src/asm/asm.1.s       | 12 ++++++++++++
 testdata/3015-amacc.S | 10 ++++++++++
 2 files changed, 22 insertions(+)
 create mode 100644 testdata/3015-amacc.S

diff --git a/src/asm/asm.1.s b/src/asm/asm.1.s
index f894fbf..7d47de5 100644
--- a/src/asm/asm.1.s
+++ b/src/asm/asm.1.s
@@ -2418,7 +2418,11 @@ addmode      php
              beq   :skipq
              cmp   #$22 ; "
              beq   :skipq
+             and   #$5f
+             cmp   #'A'
+             beq   :a
              jmp   :index
+
 :force8      lda   #amforce8
              tsb   myvalue
              jmp   :index
@@ -2435,6 +2439,14 @@ addmode      php
              tsb   myvalue
              jmp   :index
 
+*  'a' (no modifier) is ignored
+:a           iny
+             lda [lineptr],y
+             cmp #' '+1
+             jlt :zero
+             dey
+             jmp :index
+
 * skip over quoted operand component.
 :skipq       sta   :q
 :skipq1      iny
diff --git a/testdata/3015-amacc.S b/testdata/3015-amacc.S
new file mode 100644
index 0000000..d38e59e
--- /dev/null
+++ b/testdata/3015-amacc.S
@@ -0,0 +1,10 @@
+*
+* explicit a operand (inc a, etc) is dropped.
+*
+
+	inc a
+	dec a
+	lsr a
+	asl a
+	rol a
+	ror a