output variable-length bit strings

diff --git a/bits.c b/bits.c
new file mode 100644 (file)
index 0000000..2949ad5
--- /dev/null
+++ b/bits.c
@@ -0,0 +1,205 @@
+/* bits.c -- output variable-length bit strings
+ * Copyright (C) 1992-1993 Jean-loup Gailly
+ * This is free software; you can redistribute it and/or modify it under the
+ * terms of the GNU General Public License, see the file COPYING.
+ */
+
+
+/*
+ *  PURPOSE
+ *
+ *      Output variable-length bit strings. Compression can be done
+ *      to a file or to memory. (The latter is not supported in this version.)
+ *
+ *  DISCUSSION
+ *
+ *      The PKZIP "deflate" file format interprets compressed file data
+ *      as a sequence of bits.  Multi-bit strings in the file may cross
+ *      byte boundaries without restriction.
+ *
+ *      The first bit of each byte is the low-order bit.
+ *
+ *      The routines in this file allow a variable-length bit value to
+ *      be output right-to-left (useful for literal values). For
+ *      left-to-right output (useful for code strings from the tree routines),
+ *      the bits must have been reversed first with bi_reverse().
+ *
+ *      For in-memory compression, the compressed bit stream goes directly
+ *      into the requested output buffer. The input data is read in blocks
+ *      by the mem_read() function. The buffer is limited to 64K on 16 bit
+ *      machines.
+ *
+ *  INTERFACE
+ *
+ *      void bi_init (FILE *zipfile)
+ *          Initialize the bit string routines.
+ *
+ *      void send_bits (int value, int length)
+ *          Write out a bit string, taking the source bits right to
+ *          left.
+ *
+ *      int bi_reverse (int value, int length)
+ *          Reverse the bits of a bit string, taking the source bits left to
+ *          right and emitting them right to left.
+ *
+ *      void bi_windup (void)
+ *          Write out any remaining bits in an incomplete byte.
+ *
+ *      void copy_block(char *buf, unsigned len, int header)
+ *          Copy a stored block to the zip file, storing first the length and
+ *          its one's complement if requested.
+ *
+ */
+
+#include "tailor.h"
+#include "gzip.h"
+#include "crypt.h"
+
+#ifdef DEBUG
+#  include <stdio.h>
+#endif
+
+#ifdef RCSID
+static char rcsid[] = "$Id$";
+#endif
+
+/* ===========================================================================
+ * Local data used by the "bit string" routines.
+ */
+
+local file_t zfile; /* output gzip file */
+
+local unsigned short bi_buf;
+/* Output buffer. bits are inserted starting at the bottom (least significant
+ * bits).
+ */
+
+#define Buf_size (8 * 2*sizeof(char))
+/* Number of bits used within bi_buf. (bi_buf might be implemented on
+ * more than 16 bits on some systems.)
+ */
+
+local int bi_valid;
+/* Number of valid bits in bi_buf.  All bits above the last valid bit
+ * are always zero.
+ */
+
+int (*read_buf) OF((char *buf, unsigned size));
+/* Current input function. Set to mem_read for in-memory compression */
+
+#ifdef DEBUG
+  ulg bits_sent;   /* bit length of the compressed data */
+#endif
+
+/* ===========================================================================
+ * Initialize the bit string routines.
+ */
+void bi_init (zipfile)
+    file_t zipfile; /* output zip file, NO_FILE for in-memory compression */
+{
+    zfile  = zipfile;
+    bi_buf = 0;
+    bi_valid = 0;
+#ifdef DEBUG
+    bits_sent = 0L;
+#endif
+
+    /* Set the defaults for file compression. They are set by memcompress
+     * for in-memory compression.
+     */
+    if (zfile != NO_FILE) {
+       read_buf  = file_read;
+    }
+}
+
+/* ===========================================================================
+ * Send a value on a given number of bits.
+ * IN assertion: length <= 16 and value fits in length bits.
+ */
+void send_bits(value, length)
+    int value;  /* value to send */
+    int length; /* number of bits */
+{
+#ifdef DEBUG
+    Tracev((stderr," l %2d v %4x ", length, value));
+    Assert(length > 0 && length <= 15, "invalid length");
+    bits_sent += (ulg)length;
+#endif
+    /* If not enough room in bi_buf, use (valid) bits from bi_buf and
+     * (16 - bi_valid) bits from value, leaving (width - (16-bi_valid))
+     * unused bits in value.
+     */
+    if (bi_valid > (int)Buf_size - length) {
+        bi_buf |= (value << bi_valid);
+        put_short(bi_buf);
+        bi_buf = (ush)value >> (Buf_size - bi_valid);
+        bi_valid += length - Buf_size;
+    } else {
+        bi_buf |= value << bi_valid;
+        bi_valid += length;
+    }
+}
+
+/* ===========================================================================
+ * Reverse the first len bits of a code, using straightforward code (a faster
+ * method would use a table)
+ * IN assertion: 1 <= len <= 15
+ */
+unsigned bi_reverse(code, len)
+    unsigned code; /* the value to invert */
+    int len;       /* its bit length */
+{
+    register unsigned res = 0;
+    do {
+        res |= code & 1;
+        code >>= 1, res <<= 1;
+    } while (--len > 0);
+    return res >> 1;
+}
+
+/* ===========================================================================
+ * Write out any remaining bits in an incomplete byte.
+ */
+void bi_windup()
+{
+    if (bi_valid > 8) {
+        put_short(bi_buf);
+    } else if (bi_valid > 0) {
+        put_byte(bi_buf);
+    }
+    bi_buf = 0;
+    bi_valid = 0;
+#ifdef DEBUG
+    bits_sent = (bits_sent+7) & ~7;
+#endif
+}
+
+/* ===========================================================================
+ * Copy a stored block to the zip file, storing first the length and its
+ * one's complement if requested.
+ */
+void copy_block(buf, len, header)
+    char     *buf;    /* the input data */
+    unsigned len;     /* its length */
+    int      header;  /* true if block header must be written */
+{
+    bi_windup();              /* align on byte boundary */
+
+    if (header) {
+        put_short((ush)len);   
+        put_short((ush)~len);
+#ifdef DEBUG
+        bits_sent += 2*16;
+#endif
+    }
+#ifdef DEBUG
+    bits_sent += (ulg)len<<3;
+#endif
+    while (len--) {
+#ifdef CRYPT
+        int t;
+       if (key) zencode(*buf, t);
+#endif
+       put_byte(*buf++);
+    }
+}