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[libpng17] Added perfect hash code generation for lists of PNG chunks. This is

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a work in progress; checked in for use in pngfix.c
This commit is contained in:
John Bowler
2013-07-03 07:41:04 -05:00
committed by Glenn Randers-Pehrson
parent fb411867b0
commit 23f4320775
4 changed files with 541 additions and 3 deletions
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97
contrib/tools/chunkhash.h Normal file
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/* chunkhash.h -- a perfect hash code for the chunk names in png.h
*
* Last changed in libpng 1.7.0 [(PENDING RELEASE)]
*
* THIS IS A MACHINE GENERATED FILE. See contrib/tools/chunkhash.c for
* copyright and other information.
*
* USAGE: To include the PNG_CHUNK_HASH macro and associated definitions:
*
* #define PNG_CHUNKHASH_DEFS
* #include "contrib/tools/chunkhash.h"
*
* To define the png_chunk_hash array used by the macro:
*
* #define PNG_CHUNKHASH_CODE
* #include "contrib/tools/chunkhash.h"
*
* One or both of the defines must be given except when building chunkhash
* itself.
*/
#ifdef PNG_CHUNKHASH_DEFS
#ifndef PNG_CHUNKHASH_H
#define PNG_CHUNKHASH_H
/* A perfect hash code - returns a value 0..(PNG_KNOWN_CHUNK_COUNT-1) and is
* generated by the ridiculously simple program in contrib/tools/chunkhash.c
*
* The hash code used here multiplies each byte by a different constant to
* return a single number:
*
* b0 * c[0] + b1 * [c1] + b2 * c[2] + b3 * c[3]
*
* The values of the constants are found by search using the a table of
* primes, including 0, and may be (in fact are at present) 0 for some of the
* bytes, the compiler is expected to optimize multiply by zero, or one!
*
* The lookup table reduces the sparse result of the hash calculation to the
* correct index values. The chunks are indexed in the string order of the
* png_uint_32 chunk names.
*/
#define PNG_CHUNK_HASH_MASK 0x3fU
#define PNG_CHUNK_HASH_C0 103
#define PNG_CHUNK_HASH_C1 1
#define PNG_CHUNK_HASH_C2 0
#define PNG_CHUNK_HASH_C3 1
#define PNG_CHUNK_IDAT_TAG 0
#define PNG_CHUNK_IEND_TAG 1
#define PNG_CHUNK_IHDR_TAG 2
#define PNG_CHUNK_PLTE_TAG 3
#define PNG_CHUNK_bKGD_TAG 4
#define PNG_CHUNK_cHRM_TAG 5
#define PNG_CHUNK_fRAc_TAG 6
#define PNG_CHUNK_gAMA_TAG 7
#define PNG_CHUNK_gIFg_TAG 8
#define PNG_CHUNK_gIFt_TAG 9
#define PNG_CHUNK_gIFx_TAG 10
#define PNG_CHUNK_hIST_TAG 11
#define PNG_CHUNK_iCCP_TAG 12
#define PNG_CHUNK_iTXt_TAG 13
#define PNG_CHUNK_oFFs_TAG 14
#define PNG_CHUNK_pCAL_TAG 15
#define PNG_CHUNK_pHYs_TAG 16
#define PNG_CHUNK_sBIT_TAG 17
#define PNG_CHUNK_sCAL_TAG 18
#define PNG_CHUNK_sPLT_TAG 19
#define PNG_CHUNK_sRGB_TAG 20
#define PNG_CHUNK_sTER_TAG 21
#define PNG_CHUNK_tEXt_TAG 22
#define PNG_CHUNK_tIME_TAG 23
#define PNG_CHUNK_tRNS_TAG 24
#define PNG_CHUNK_zTXt_TAG 25
#define PNG_KNOWN_CHUNK_COUNT 26
extern const png_byte png_chunk_hash[PNG_CHUNK_HASH_MASK+1];
#endif /* !PNG_CHUNKHASH_H */
#endif /* PNG_CHUNKHASH_DEFS */
#ifndef PNG_CHUNK_HASH
#define PNG_CHUNK_HASH(chunk) (png_chunk_hash[PNG_CHUNK_HASH_MASK & (\
((chunk) >> 24) * PNG_CHUNK_HASH_C0 +\
((chunk) >> 16) * PNG_CHUNK_HASH_C1 +\
((chunk) >> 8) * PNG_CHUNK_HASH_C2 +\
((chunk) ) * PNG_CHUNK_HASH_C3)])
#endif
#ifdef PNG_CHUNKHASH_CODE
#ifndef PNG_CHUNKHASH_C
#define PNG_CHUNKHASH_C
const png_byte png_chunk_hash[PNG_CHUNK_HASH_MASK+1] = {
26, 3, 26, 26, 26, 26, 26, 13, 26, 26, 26, 16, 26, 26, 26, 26,
26, 24, 12, 26, 18, 26, 26, 26, 26, 20, 26, 17, 26, 26, 25, 15,
26, 8, 14, 26, 26, 22, 26, 26, 1, 19, 5, 21, 26, 26, 9, 26,
26, 26, 10, 7, 26, 11, 26, 0, 26, 2, 23, 26, 26, 4, 26, 6
};
#endif /* !PNG_CHUNKHASH_C */
#endif /* PNG_CHUNKHASH_CODE */