Fossil SCM

fossil-scm / compat / zlib / examples / zran.h

Source Blame History 53 lines

6ea30fb…	florian	1	/* zran.h -- example of deflate stream indexing and random access
6ea30fb…	florian	2	* Copyright (C) 2005, 2012, 2018, 2023, 2024, 2025 Mark Adler
adb9e8e…	drh	3	* For conditions of distribution and use, see copyright notice in zlib.h
6ea30fb…	florian	4	* Version 1.7 16 May 2025 Mark Adler */
adb9e8e…	drh	5
adb9e8e…	drh	6	#include <stdio.h>
adb9e8e…	drh	7	#include "zlib.h"
adb9e8e…	drh	8
f1f1d6c…	drh	9	// Access point.
f1f1d6c…	drh	10	typedef struct point {
f1f1d6c…	drh	11	off_t out; // offset in uncompressed data
f1f1d6c…	drh	12	off_t in; // offset in compressed file of first full byte
f1f1d6c…	drh	13	int bits; // 0, or number of bits (1-7) from byte at in-1
6ea30fb…	florian	14	unsigned dict; // number of bytes in window to use as a dictionary
6ea30fb…	florian	15	unsigned char *window; // preceding 32K (or less) of uncompressed data
f1f1d6c…	drh	16	} point_t;
f1f1d6c…	drh	17
f1f1d6c…	drh	18	// Access point list.
adb9e8e…	drh	19	struct deflate_index {
f1f1d6c…	drh	20	int have; // number of access points in list
f1f1d6c…	drh	21	int mode; // -15 for raw, 15 for zlib, or 31 for gzip
f1f1d6c…	drh	22	off_t length; // total length of uncompressed data
f1f1d6c…	drh	23	point_t *list; // allocated list of access points
6ea30fb…	florian	24	z_stream strm; // re-usable inflate engine for extraction
adb9e8e…	drh	25	};
adb9e8e…	drh	26
f1f1d6c…	drh	27	// Make one pass through a zlib, gzip, or raw deflate compressed stream and
f1f1d6c…	drh	28	// build an index, with access points about every span bytes of uncompressed
f1f1d6c…	drh	29	// output. gzip files with multiple members are fully indexed. span should be
f1f1d6c…	drh	30	// chosen to balance the speed of random access against the memory requirements
f1f1d6c…	drh	31	// of the list, which is about 32K bytes per access point. The return value is
f1f1d6c…	drh	32	// the number of access points on success (>= 1), Z_MEM_ERROR for out of
f1f1d6c…	drh	33	// memory, Z_BUF_ERROR for a premature end of input, Z_DATA_ERROR for a format
f1f1d6c…	drh	34	// or verification error in the input file, or Z_ERRNO for a file read error.
6ea30fb…	florian	35	// On success, *built points to the resulting index, otherwise it's NULL.
adb9e8e…	drh	36	int deflate_index_build(FILE in, off_t span, struct deflate_index *built);
adb9e8e…	drh	37
f1f1d6c…	drh	38	// Use the index to read len bytes from offset into buf. Return the number of
f1f1d6c…	drh	39	// bytes read or a negative error code. If data is requested past the end of
f1f1d6c…	drh	40	// the uncompressed data, then deflate_index_extract() will return a value less
f1f1d6c…	drh	41	// than len, indicating how much was actually read into buf. If given a valid
f1f1d6c…	drh	42	// index, this function should not return an error unless the file was modified
f1f1d6c…	drh	43	// somehow since the index was generated, given that deflate_index_build() had
f1f1d6c…	drh	44	// validated all of the input. If nevertheless there is a failure, Z_BUF_ERROR
f1f1d6c…	drh	45	// is returned if the compressed data ends prematurely, Z_DATA_ERROR if the
f1f1d6c…	drh	46	// deflate compressed data is not valid, Z_MEM_ERROR if out of memory,
f1f1d6c…	drh	47	// Z_STREAM_ERROR if the index is not valid, or Z_ERRNO if there is an error
f1f1d6c…	drh	48	// reading or seeking on the input file.
f1f1d6c…	drh	49	ptrdiff_t deflate_index_extract(FILE in, struct deflate_index index,
f1f1d6c…	drh	50	off_t offset, unsigned char *buf, size_t len);
f1f1d6c…	drh	51
f1f1d6c…	drh	52	// Deallocate an index built by deflate_index_build().
f1f1d6c…	drh	53	void deflate_index_free(struct deflate_index *index);

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