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Library/zlib-1.3.1/examples/zran.h

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+/* zran.h -- example of deflated 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 */
+
+#include <stdio.h>
+#include "zlib.h"
+
+// Access point.
+typedef struct point {
+    off_t out;          // offset in uncompressed data
+    off_t in;           // offset in compressed file of first full byte
+    int bits;           // 0, or number of bits (1-7) from byte at in-1
+    unsigned char window[32768];    // preceding 32K of uncompressed data
+} point_t;
+
+// Access point list.
+struct deflate_index {
+    int have;           // number of access points in list
+    int mode;           // -15 for raw, 15 for zlib, or 31 for gzip
+    off_t length;       // total length of uncompressed data
+    point_t *list;      // allocated list of access points
+};
+
+// Make one pass through a zlib, gzip, or raw deflate compressed stream and
+// build an index, with access points about every span bytes of uncompressed
+// output. gzip files with multiple members are fully indexed. span should be
+// chosen to balance the speed of random access against the memory requirements
+// of the list, which is about 32K bytes per access point. The return value is
+// the number of access points on success (>= 1), Z_MEM_ERROR for out of
+// memory, Z_BUF_ERROR for a premature end of input, Z_DATA_ERROR for a format
+// or verification error in the input file, or Z_ERRNO for a file read error.
+// On success, *built points to the resulting index.
+int deflate_index_build(FILE *in, off_t span, struct deflate_index **built);
+
+// Use the index to read len bytes from offset into buf. Return the number of
+// bytes read or a negative error code. If data is requested past the end of
+// the uncompressed data, then deflate_index_extract() will return a value less
+// than len, indicating how much was actually read into buf. If given a valid
+// index, this function should not return an error unless the file was modified
+// somehow since the index was generated, given that deflate_index_build() had
+// validated all of the input. If nevertheless there is a failure, Z_BUF_ERROR
+// is returned if the compressed data ends prematurely, Z_DATA_ERROR if the
+// deflate compressed data is not valid, Z_MEM_ERROR if out of memory,
+// Z_STREAM_ERROR if the index is not valid, or Z_ERRNO if there is an error
+// reading or seeking on the input file.
+ptrdiff_t deflate_index_extract(FILE *in, struct deflate_index *index,
+                                off_t offset, unsigned char *buf, size_t len);
+
+// Deallocate an index built by deflate_index_build().
+void deflate_index_free(struct deflate_index *index);