1 files changed, 95 insertions, 0 deletions
diff --git a/swap.c b/swap.c
new file mode 100644
index 0000000..28aad1b
--- /dev/null
+++ b/swap.c
@@ -0,0 +1,95 @@
+/*  Copyright 2021 Alain Knaff.
+ *  This file is part of mtools.
+ *
+ *  Mtools is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  Mtools is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with Mtools.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * filter to support byte-swapped filesystems
+ */
+
+#include "sysincludes.h"
+#include "msdos.h"
+#include "mtools.h"
+#include "swap.h"
+
+typedef struct Swap_t {
+	struct Stream_t head;
+} Swap_t;
+
+static void swap_buffer(char *buf, size_t len)
+{
+	unsigned int i;
+	for (i=0; i<len; i+=2) {
+		char temp = buf[i];
+		buf[i] = buf[i+1];
+		buf[i+1] = temp;
+	}
+}
+
+
+static ssize_t swap_pread(Stream_t *Stream, char *buf,
+			  mt_off_t where, size_t len)
+{
+	DeclareThis(Swap_t);
+
+	ssize_t result = PREADS(This->head.Next, buf, where, len);
+	if(result < 0)
+		return result;
+	swap_buffer( buf, (size_t) result);
+	return result;
+}
+
+static ssize_t swap_pwrite(Stream_t *Stream, char *buf,
+			  mt_off_t where, size_t len)
+{
+	DeclareThis(Swap_t);
+
+	ssize_t result;
+	char *swapping = malloc( len );
+	memcpy( swapping, buf, len );
+	swap_buffer( swapping, len );
+
+	result = PWRITES(This->head.Next, swapping, where, len);
+
+	free(swapping);
+	return result;
+}
+
+
+static Class_t SwapClass = {
+	0,
+	0,
+	swap_pread,
+	swap_pwrite,
+	0, /* flush */
+	0, /* free */
+	set_geom_pass_through, /* set_geom */
+	0, /* get_data */
+	0, /* pre-allocate */
+	get_dosConvert_pass_through, /* dos convert */
+	0, /* discard */
+};
+
+Stream_t *OpenSwap(Stream_t *Next) {
+	Swap_t *This;
+
+	This = New(Swap_t);
+	if (!This){
+		printOom();
+		return 0;
+	}
+	memset((void*)This, 0, sizeof(Swap_t));
+	init_head(&This->head, &SwapClass, Next);
+
+	return &This->head;
+}