Add a NOPRIME #define to zran.c to not use inflatePrime().
This supports zlib versions earlier than 1.2.3 (July 2005), as
well as incomplete clones of zlib that do not have inflatePrime().
diff --git a/examples/zran.c b/examples/zran.c
index 1ffba7f..32c9368 100644
--- a/examples/zran.c
+++ b/examples/zran.c
@@ -1,7 +1,7 @@
/* zran.c -- example of deflate stream indexing and random access
* Copyright (C) 2005, 2012, 2018, 2023 Mark Adler
* For conditions of distribution and use, see copyright notice in zlib.h
- * Version 1.3 18 Feb 2023 Mark Adler */
+ * Version 1.4 13 Apr 2023 Mark Adler */
/* Version History:
1.0 29 May 2005 First version
@@ -13,6 +13,7 @@
Support a size_t size when extracting (was an int)
Do a binary search over the index for an access point
Expose the access point type to enable save and load
+ 1.4 13 Apr 2023 Add a NOPRIME define to not use inflatePrime()
*/
// Illustrate the use of Z_BLOCK, inflatePrime(), and inflateSetDictionary()
@@ -237,6 +238,94 @@
return index->have;
}
+#ifdef NOPRIME
+// Support zlib versions before 1.2.3 (July 2005), or incomplete zlib clones
+// that do not have inflatePrime().
+
+# define INFLATEPRIME inflatePreface
+
+// Append the low bits bits of value to in[] at bit position *have, updating
+// *have. value must be zero above its low bits bits. bits must be positive.
+// This assumes that any bits above the *have bits in the last byte are zeros.
+// That assumption is preserved on return, as any bits above *have + bits in
+// the last byte written will be set to zeros.
+static inline void append_bits(unsigned value, int bits,
+ unsigned char *in, int *have) {
+ in += *have >> 3; // where the first bits from value will go
+ int k = *have & 7; // the number of bits already there
+ *have += bits;
+ if (k)
+ *in |= value << k; // write value above the low k bits
+ else
+ *in = value;
+ k = 8 - k; // the number of bits just appended
+ while (bits > k) {
+ value >>= k; // drop the bits appended
+ bits -= k;
+ k = 8; // now at a byte boundary
+ *++in = value;
+ }
+}
+
+// Insert enough bits in the form of empty deflate blocks in front of the the
+// low bits bits of value, in order to bring the sequence to a byte boundary.
+// Then feed that to inflate(). This does what inflatePrime() does, except that
+// a negative value of bits is not supported. bits must be in 0..16. If the
+// arguments are invalid, Z_STREAM_ERROR is returned. Otherwise the return
+// value from inflate() is returned.
+static int inflatePreface(z_stream *strm, int bits, int value) {
+ // Check input.
+ if (strm == Z_NULL || bits < 0 || bits > 16)
+ return Z_STREAM_ERROR;
+ if (bits == 0)
+ return Z_OK;
+ value &= (2 << (bits - 1)) - 1;
+
+ // An empty dynamic block with an odd number of bits (95). The high bit of
+ // the last byte is unused.
+ static const unsigned char dyn[] = {
+ 4, 0xe0, 0x81, 8, 0, 0, 0, 0, 0x20, 0xa8, 0xab, 0x1f
+ };
+ const int dynlen = 95; // number of bits in the block
+
+ // Build an input buffer for inflate that is a multiple of eight bits in
+ // length, and that ends with the low bits bits of value.
+ unsigned char in[(dynlen + 3 * 10 + 16 + 7) / 8];
+ int have = 0;
+ if (bits & 1) {
+ // Insert an empty dynamic block to get to an odd number of bits, so
+ // when bits bits from value are appended, we are at an even number of
+ // bits.
+ memcpy(in, dyn, sizeof(dyn));
+ have = dynlen;
+ }
+ while ((have + bits) & 7)
+ // Insert empty fixed blocks until appending bits bits would put us on
+ // a byte boundary. This will insert at most three fixed blocks.
+ append_bits(2, 10, in, &have);
+
+ // Append the bits bits from value, which takes us to a byte boundary.
+ append_bits(value, bits, in, &have);
+
+ // Deliver the input to inflate(). There is no output space provided, but
+ // inflate() can't get stuck waiting on output not ingesting all of the
+ // provided input. The reason is that there will be at most 16 bits of
+ // input from value after the empty deflate blocks (which themselves
+ // generate no output). At least ten bits are needed to generate the first
+ // output byte from a fixed block. The last two bytes of the buffer have to
+ // be ingested in order to get ten bits, which is the most that value can
+ // occupy.
+ strm->avail_in = have >> 3;
+ strm->next_in = in;
+ strm->avail_out = 0;
+ strm->next_out = in; // not used, but can't be NULL
+ return inflate(strm, Z_NO_FLUSH);
+}
+
+#else
+# define INFLATEPRIME inflatePrime
+#endif
+
// See comments in zran.h.
ptrdiff_t deflate_index_extract(FILE *in, struct deflate_index *index,
off_t offset, unsigned char *buf, size_t len) {
@@ -272,7 +361,7 @@
if (ret != Z_OK)
return ret;
if (point->bits)
- inflatePrime(&strm, point->bits, ch >> (8 - point->bits));
+ INFLATEPRIME(&strm, point->bits, ch >> (8 - point->bits));
inflateSetDictionary(&strm, point->window, WINSIZE);
// Skip uncompressed bytes until offset reached, then satisfy request.
