From e2da2bffe58a76c091d3496bd3ca2d2f18ea2eb6 Mon Sep 17 00:00:00 2001
From: "B. Watson" <urchlay@slackware.uk>
Date: Thu, 13 Nov 2025 05:39:38 -0500
Subject: initial commit

---
 src/io.c | 92 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 92 insertions(+)
 create mode 100644 src/io.c

(limited to 'src/io.c')

diff --git a/src/io.c b/src/io.c
new file mode 100644
index 0000000..9b8e40e
--- /dev/null
+++ b/src/io.c
@@ -0,0 +1,92 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <f65.h>
+#include "unalf.h"
+#include "addrs.h"
+
+static int headers_read = 0;
+
+static void die_arc(void) {
+	fprintf(stderr, "%s: this is an ARC file, not ALF\n", self);
+	exit(1);
+}
+
+static void die_not_alf(void) {
+	fprintf(stderr, "%s: not an ALF file\n", self);
+	exit(1);
+}
+
+static void eof_junk(void) {
+	fprintf(stderr, "%s: junk at EOF (ignoring)\n", self);
+}
+
+/* return 1 if a header is read, 0 if not */
+int read_alf_header(void) {
+	u8 h1, h2;
+	int bytes;
+
+	bytes = fread(mem + alf_header, 1, 29, in_file);
+
+	if(!bytes) {
+		if(headers_read)
+			return 0;
+		else
+			die_not_alf();
+	} else if(bytes < 29) {
+		if(headers_read) {
+			eof_junk();
+			return 0;
+		} else {
+			die_not_alf();
+		}
+	}
+
+	h1 = mem[alf_header];
+	h2 = mem[alf_hdr_sig];
+
+	if(h1 == 0x1a) {
+		if(h2 < 0x0f) die_arc();
+		if(h2 == 0x0f) {
+			headers_read++;
+			return 1; /* signature matches */
+		}
+	}
+
+	if(headers_read)
+		eof_junk();
+	else
+		die_not_alf();
+
+	return 0;
+}
+
+/* read buf_len_l/h bytes into buf_adr_l/h, then store the number
+   of bytes actually read in buf_len_l/h. TODO: what about EOF? */
+void readblock(void) {
+	int bytes, len, bufadr;
+	u8 *buf;
+
+	bufadr = dpeek(buf_adr_l);
+	buf = mem + bufadr;
+	len = dpeek(buf_len_l);
+
+	// fprintf(stderr, "readblock, bufadr = $%04x, len = $%04x\n", bufadr, len);
+
+	bytes = fread(buf, 1, len, in_file);
+	dpoke(buf_len_l, bytes);
+}
+
+/* mirror of readblock() */
+void writeblock(void) {
+	int bytes, len, bufadr;
+	u8 *buf;
+
+	bufadr = dpeek(buf_adr_l);
+	buf = mem + bufadr;
+	len = dpeek(buf_len_l);
+
+	// fprintf(stderr, "writeblock, bufadr = $%04x, len = $%04x\n", bufadr, len);
+
+	bytes = fwrite(buf, 1, len, out_file);
+	dpoke(buf_len_l, bytes);
+}
-- 
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