From 5d7ee4168b03ed7d95da3425d843bec5743eaeb6 Mon Sep 17 00:00:00 2001
From: Thomas Voss <mail@thomasvoss.com>
Date: Wed, 14 Feb 2024 00:43:35 +0100
Subject: Align opcodes on even byte boundaries

---
 src/c8asm/assembler.c | 9 +++++++++
 1 file changed, 9 insertions(+)

(limited to 'src')

diff --git a/src/c8asm/assembler.c b/src/c8asm/assembler.c
index ea292b7..2e8693b 100644
--- a/src/c8asm/assembler.c
+++ b/src/c8asm/assembler.c
@@ -77,6 +77,8 @@ assemble(FILE *stream, struct ast ast)
 		fwrite(&__x, 1, sizeof(__x), stream); \
 	} while (false)
 
+	bool pad = false;
+
 	da_foreach (&ast, node) {
 		if (node->kind == D_LABEL) {
 			struct label lbl = {
@@ -96,6 +98,11 @@ assemble(FILE *stream, struct ast ast)
 		if (node->kind != D_INSTR)
 			unreachable();
 
+		/* Instructions need to be 0-padded so they appear on an even byte
+		   boundary. */
+		if (node->instr.kind != I_DB && pad)
+			putchar(0);
+
 		switch (node->instr.kind) {
 		case I_ADD_I_VX:
 			PUT(0xF01E | (node->instr.args[0].val << 8));
@@ -124,6 +131,8 @@ assemble(FILE *stream, struct ast ast)
 		case I_DB:
 			da_foreach (&node->instr, byte)
 				fputc(*byte, stream);
+			if (node->instr.len & 1)
+				pad = !pad;
 			break;
 		case I_DRW:
 			PUT(0xD000 | (node->instr.args[0].val << 8)
-- 
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