diff --git a/demo/.gitignore b/demo/.gitignore
index ca81873..27390e7 100644
--- a/demo/.gitignore
+++ b/demo/.gitignore
@@ -1,2 +1,3 @@
 dwarf-synthesis
 tests/data*
+tests/*.synth
diff --git a/demo/zip.c b/demo/zip.c
new file mode 100644
index 0000000..be5c4b0
--- /dev/null
+++ b/demo/zip.c
@@ -0,0 +1,132 @@
+/* zip.c -- compress files to the gzip or pkzip format
+
+   Copyright (C) 1997-1999, 2006-2007, 2009-2018 Free Software Foundation, Inc.
+   Copyright (C) 1992-1993 Jean-loup Gailly
+
+   This program 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, or (at your option)
+   any later version.
+
+   This program 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 this program; if not, write to the Free Software Foundation,
+   Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
+
+#include <config.h>
+#include <ctype.h>
+
+#include "tailor.h"
+#include "gzip.h"
+
+local ulg crc;       /* crc on uncompressed file data */
+off_t header_bytes;   /* number of bytes in gzip header */
+
+/* ===========================================================================
+ * Deflate in to out.
+ * IN assertions: the input and output buffers are cleared.
+ *   The variables time_stamp and save_orig_name are initialized.
+ */
+int zip(in, out)
+    int in, out;            /* input and output file descriptors */
+{
+    uch  flags = 0;         /* general purpose bit flags */
+    ush  attr = 0;          /* ascii/binary flag */
+    ush  deflate_flags = 0; /* pkzip -es, -en or -ex equivalent */
+    ulg  stamp;
+
+    ifd = in;
+    ofd = out;
+    outcnt = 0;
+
+    /* Write the header to the gzip file. See algorithm.doc for the format */
+
+    method = DEFLATED;
+    put_byte(GZIP_MAGIC[0]); /* magic header */
+    put_byte(GZIP_MAGIC[1]);
+    put_byte(DEFLATED);      /* compression method */
+
+    if (save_orig_name) {
+        flags |= ORIG_NAME;
+    }
+    put_byte(flags);         /* general flags */
+    if (time_stamp.tv_nsec < 0)
+      stamp = 0;
+    else if (0 < time_stamp.tv_sec && time_stamp.tv_sec <= 0xffffffff)
+      stamp = time_stamp.tv_sec;
+    else
+      {
+        /* It's intended that timestamp 0 generates this warning,
+           since gzip format reserves 0 for something else.  */
+        warning ("file timestamp out of range for gzip format");
+        stamp = 0;
+      }
+    put_long (stamp);
+
+    /* Write deflated file to zip file */
+    crc = updcrc(0, 0);
+
+    bi_init(out);
+    ct_init(&attr, &method);
+    lm_init(level, &deflate_flags);
+
+    put_byte((uch)deflate_flags); /* extra flags */
+    put_byte(OS_CODE);            /* OS identifier */
+
+    if (save_orig_name) {
+        char *p = gzip_base_name (ifname); /* Don't save the directory part. */
+        do {
+            put_byte (*p);
+        } while (*p++);
+    }
+    header_bytes = (off_t)outcnt;
+
+    (void)deflate();
+
+#ifndef NO_SIZE_CHECK
+  /* Check input size
+   * (but not on MSDOS -- diet in TSR mode reports an incorrect file size)
+   */
+    if (ifile_size != -1L && bytes_in != ifile_size) {
+        fprintf(stderr, "%s: %s: file size changed while zipping\n",
+                program_name, ifname);
+    }
+#endif
+
+    /* Write the crc and uncompressed size */
+    put_long(crc);
+    put_long((ulg)bytes_in);
+    header_bytes += 2*4;
+
+    flush_outbuf();
+    return OK;
+}
+
+
+/* ===========================================================================
+ * Read a new buffer from the current input file, perform end-of-line
+ * translation, and update the crc and input file size.
+ * IN assertion: size >= 2 (for end-of-line translation)
+ */
+int file_read(buf, size)
+    char *buf;
+    unsigned size;
+{
+    unsigned len;
+
+    Assert(insize == 0, "inbuf not empty");
+
+    len = read_buffer (ifd, buf, size);
+    if (len == 0) return (int)len;
+    if (len == (unsigned)-1) {
+        read_error();
+    }
+
+    crc = updcrc((uch*)buf, len);
+    bytes_in += (off_t)len;
+    return (int)len;
+}