/src/hdf5/src/H5checksum.c

Source
/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
 * Copyright by The HDF Group.                                               *
 * All rights reserved.                                                      *
 *                                                                           *
 * This file is part of HDF5.  The full HDF5 copyright notice, including     *
 * terms governing use, modification, and redistribution, is contained in    *
 * the LICENSE file, which can be found at the root of the source code       *
 * distribution tree, or in https://www.hdfgroup.org/licenses.               *
 * If you do not have access to either file, you may request a copy from     *
 * help@hdfgroup.org.                                                        *
 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */

/*-------------------------------------------------------------------------
 *
 * Created:   H5checksum.c
 *
 * Purpose:   Internal code for computing fletcher32 checksums
 *
 *-------------------------------------------------------------------------
 */

/****************/
/* Module Setup */
/****************/
#include "H5module.h" /* This source code file is part of the H5 module */

/***********/
/* Headers */
/***********/
#include "H5private.h" /* Generic Functions     */

/****************/
/* Local Macros */
/****************/

/* Polynomial quotient */
/* (same as the IEEE 802.3 (Ethernet) quotient) */
#define H5_CRC_QUOTIENT 0x04C11DB7

/******************/
/* Local Typedefs */
/******************/

/********************/
/* Package Typedefs */
/********************/

/********************/
/* Local Prototypes */
/********************/

/*********************/
/* Package Variables */
/*********************/

/*****************************/
/* Library Private Variables */
/*****************************/

/*******************/
/* Local Variables */
/*******************/

/* Table of CRCs of all 8-bit messages. */
static uint32_t H5_crc_table[256];

/* Flag: has the table been computed? */
static bool H5_crc_table_computed = false;

/*-------------------------------------------------------------------------
 * Function:  H5_checksum_fletcher32
 *
 * Purpose: This routine provides a generic, fast checksum algorithm for
 *              use in the library.
 *
 * Note:        See the Wikipedia page for Fletcher's checksum:
 *                  http://en.wikipedia.org/wiki/Fletcher%27s_checksum
 *              for more details, etc.
 *
 * Note #2:     Per the information in RFC 3309:
 *                      (http://tools.ietf.org/html/rfc3309)
 *              Fletcher's checksum is not reliable for small buffers.
 *
 * Note #3:     The algorithm below differs from that given in the Wikipedia
 *              page by copying the data into 'sum1' in a more portable way
 *              and also by initializing 'sum1' and 'sum2' to 0 instead of
 *              0xffff (for backward compatibility reasons with earlier
 *              HDF5 fletcher32 I/O filter routine, mostly).
 *
 * Return:  32-bit fletcher checksum of input buffer (can't fail)
 *
 *-------------------------------------------------------------------------
 */
uint32_t
H5_checksum_fletcher32(const void *_data, size_t _len)
{
    const uint8_t *data = (const uint8_t *)_data; /* Pointer to the data to be summed */
    size_t         len  = _len / 2;               /* Length in 16-bit words */
    uint32_t       sum1 = 0, sum2 = 0;

    FUNC_ENTER_NOAPI_NOINIT_NOERR

    /* Sanity check */
    assert(_data);
    assert(_len > 0);

    /* Compute checksum for pairs of bytes */
    /* (the magic "360" value is the largest number of sums that can be
     *  performed without numeric overflow)
     */
    while (len) {
        size_t tlen = len > 360 ? 360 : len;
        len -= tlen;
        do {
            sum1 += (uint32_t)(((uint16_t)data[0]) << 8) | ((uint16_t)data[1]);
            data += 2;
            sum2 += sum1;
        } while (--tlen);
        sum1 = (sum1 & 0xffff) + (sum1 >> 16);
        sum2 = (sum2 & 0xffff) + (sum2 >> 16);
    }

    /* Check for odd # of bytes */
    if (_len % 2) {
        sum1 += (uint32_t)(((uint16_t)*data) << 8);
        sum2 += sum1;
        sum1 = (sum1 & 0xffff) + (sum1 >> 16);
        sum2 = (sum2 & 0xffff) + (sum2 >> 16);
    } /* end if */

    /* Second reduction step to reduce sums to 16 bits */
    sum1 = (sum1 & 0xffff) + (sum1 >> 16);
    sum2 = (sum2 & 0xffff) + (sum2 >> 16);

    FUNC_LEAVE_NOAPI((sum2 << 16) | sum1)
} /* end H5_checksum_fletcher32() */

/*-------------------------------------------------------------------------
 * Function:  H5__checksum_crc_make_table
 *
 * Purpose: Compute the CRC table for the CRC checksum algorithm
 *
 * Return:  none
 *
 *-------------------------------------------------------------------------
 */
static void
H5__checksum_crc_make_table(void)
{
    uint32_t c;    /* Checksum for each byte value */
    unsigned n, k; /* Local index variables */

    FUNC_ENTER_PACKAGE_NOERR

    /* Compute the checksum for each possible byte value */
    for (n = 0; n < 256; n++) {
        c = (uint32_t)n;
        for (k = 0; k < 8; k++)
            if (c & 1)
                c = H5_CRC_QUOTIENT ^ (c >> 1);
            else
                c = c >> 1;
        H5_crc_table[n] = c;
    }
    H5_crc_table_computed = true;

    FUNC_LEAVE_NOAPI_VOID
} /* end H5__checksum_crc_make_table() */

/*-------------------------------------------------------------------------
 * Function:  H5__checksum_crc_update
 *
 * Purpose: Update a running CRC with the bytes buf[0..len-1]--the CRC
 *              should be initialized to all 1's, and the transmitted value
 *              is the 1's complement of the final running CRC (see the
 *              H5_checksum_crc() routine below)).
 *
 * Return:  32-bit CRC checksum of input buffer (can't fail)
 *
 *-------------------------------------------------------------------------
 */
static uint32_t
H5__checksum_crc_update(uint32_t crc, const uint8_t *buf, size_t len)
{
    size_t n; /* Local index variable */

    FUNC_ENTER_PACKAGE_NOERR

    /* Initialize the CRC table if necessary */
    if (!H5_crc_table_computed)
        H5__checksum_crc_make_table();

    /* Update the CRC with the results from this buffer */
    for (n = 0; n < len; n++)
        crc = H5_crc_table[(crc ^ buf[n]) & 0xff] ^ (crc >> 8);

    FUNC_LEAVE_NOAPI(crc)
} /* end H5__checksum_crc_update() */

/*-------------------------------------------------------------------------
 * Function:  H5_checksum_crc
 *
 * Purpose: This routine provides a generic checksum algorithm for
 *              use in the library.
 *
 * Note:        This algorithm was based on the implementation described
 *              in the document describing the PNG image format:
 *                  http://www.w3.org/TR/PNG/#D-CRCAppendix
 *
 * Return:  32-bit CRC checksum of input buffer (can't fail)
 *
 *-------------------------------------------------------------------------
 */
uint32_t
H5_checksum_crc(const void *_data, size_t len)
{
    FUNC_ENTER_NOAPI_NOINIT_NOERR

    /* Sanity check */
    assert(_data);
    assert(len > 0);

    FUNC_LEAVE_NOAPI(H5__checksum_crc_update((uint32_t)0xffffffffL, (const uint8_t *)_data, len) ^
                     0xffffffffL)
} /* end H5_checksum_crc() */

/*
-------------------------------------------------------------------------------
H5_lookup3_mix -- mix 3 32-bit values reversibly.

This is reversible, so any information in (a,b,c) before mix() is
still in (a,b,c) after mix().

If four pairs of (a,b,c) inputs are run through mix(), or through
mix() in reverse, there are at least 32 bits of the output that
are sometimes the same for one pair and different for another pair.
This was tested for:
* pairs that differed by one bit, by two bits, in any combination
  of top bits of (a,b,c), or in any combination of bottom bits of
  (a,b,c).
* "differ" is defined as +, -, ^, or ~^.  For + and -, I transformed
  the output delta to a Gray code (a^(a>>1)) so a string of 1's (as
  is commonly produced by subtraction) look like a single 1-bit
  difference.
* the base values were pseudorandom, all zero but one bit set, or
  all zero plus a counter that starts at zero.

Some k values for my "a-=c; a^=rot(c,k); c+=b;" arrangement that
satisfy this are
    4  6  8 16 19  4
    9 15  3 18 27 15
   14  9  3  7 17  3
Well, "9 15 3 18 27 15" didn't quite get 32 bits diffing
for "differ" defined as + with a one-bit base and a two-bit delta.  I
used http://burtleburtle.net/bob/hash/avalanche.html to choose
the operations, constants, and arrangements of the variables.

This does not achieve avalanche.  There are input bits of (a,b,c)
that fail to affect some output bits of (a,b,c), especially of a.  The
most thoroughly mixed value is c, but it doesn't really even achieve
avalanche in c.

This allows some parallelism.  Read-after-writes are good at doubling
the number of bits affected, so the goal of mixing pulls in the opposite
direction as the goal of parallelism.  I did what I could.  Rotates
seem to cost as much as shifts on every machine I could lay my hands
on, and rotates are much kinder to the top and bottom bits, so I used
rotates.
-------------------------------------------------------------------------------
*/
#define H5_lookup3_rot(x, k) (((x) << (k)) ^ ((x) >> (32 - (k))))
#define H5_lookup3_mix(a, b, c)                                                                              \
    do {                                                                                                     \
        a -= c;                                                                                              \
        a ^= H5_lookup3_rot(c, 4);                                                                           \
        c += b;                                                                                              \
        b -= a;                                                                                              \
        b ^= H5_lookup3_rot(a, 6);                                                                           \
        a += c;                                                                                              \
        c -= b;                                                                                              \
        c ^= H5_lookup3_rot(b, 8);                                                                           \
        b += a;                                                                                              \
        a -= c;                                                                                              \
        a ^= H5_lookup3_rot(c, 16);                                                                          \
        c += b;                                                                                              \
        b -= a;                                                                                              \
        b ^= H5_lookup3_rot(a, 19);                                                                          \
        a += c;                                                                                              \
        c -= b;                                                                                              \
        c ^= H5_lookup3_rot(b, 4);                                                                           \
        b += a;                                                                                              \
    } while (0)

/*
-------------------------------------------------------------------------------
H5_lookup3_final -- final mixing of 3 32-bit values (a,b,c) into c

Pairs of (a,b,c) values differing in only a few bits will usually
produce values of c that look totally different.  This was tested for
* pairs that differed by one bit, by two bits, in any combination
  of top bits of (a,b,c), or in any combination of bottom bits of
  (a,b,c).
* "differ" is defined as +, -, ^, or ~^.  For + and -, I transformed
  the output delta to a Gray code (a^(a>>1)) so a string of 1's (as
  is commonly produced by subtraction) look like a single 1-bit
  difference.
* the base values were pseudorandom, all zero but one bit set, or
  all zero plus a counter that starts at zero.

These constants passed:
 14 11 25 16 4 14 24
 12 14 25 16 4 14 24
and these came close:
  4  8 15 26 3 22 24
 10  8 15 26 3 22 24
 11  8 15 26 3 22 24
-------------------------------------------------------------------------------
*/
#define H5_lookup3_final(a, b, c)                                                                            \
    do {                                                                                                     \
        c ^= b;                                                                                              \
        c -= H5_lookup3_rot(b, 14);                                                                          \
        a ^= c;                                                                                              \
        a -= H5_lookup3_rot(c, 11);                                                                          \
        b ^= a;                                                                                              \
        b -= H5_lookup3_rot(a, 25);                                                                          \
        c ^= b;                                                                                              \
        c -= H5_lookup3_rot(b, 16);                                                                          \
        a ^= c;                                                                                              \
        a -= H5_lookup3_rot(c, 4);                                                                           \
        b ^= a;                                                                                              \
        b -= H5_lookup3_rot(a, 14);                                                                          \
        c ^= b;                                                                                              \
        c -= H5_lookup3_rot(b, 24);                                                                          \
    } while (0)

/*
-------------------------------------------------------------------------------
H5_checksum_lookup3() -- hash a variable-length key into a 32-bit value
  k       : the key (the unaligned variable-length array of bytes)
  length  : the length of the key, counting by bytes
  initval : can be any 4-byte value
Returns a 32-bit value.  Every bit of the key affects every bit of
the return value.  Two keys differing by one or two bits will have
totally different hash values.

The best hash table sizes are powers of 2.  There is no need to do
mod a prime (mod is so slow!).  If you need less than 32 bits,
use a bitmask.  For example, if you need only 10 bits, do
  h = (h & hashmask(10));
In which case, the hash table should have hashsize(10) elements.

If you are hashing n strings (uint8_t **)k, do it like this:
  for (i=0, h=0; i<n; ++i) h = H5_checksum_lookup( k[i], len[i], h);

By Bob Jenkins, 2006.  bob_jenkins@burtleburtle.net.  You may use this
code any way you wish, private, educational, or commercial.  It's free.

Use for hash table lookup, or anything where one collision in 2^^32 is
acceptable.  Do NOT use for cryptographic purposes.
-------------------------------------------------------------------------------
*/

uint32_t
H5_checksum_lookup3(const void *key, size_t length, uint32_t initval)
{
    const uint8_t *k = (const uint8_t *)key;
    uint32_t       a, b, c = 0; /* internal state */

    FUNC_ENTER_NOAPI_NOINIT_NOERR

    /* Sanity check */
    assert(key);
    assert(length > 0);

    /* Set up the internal state */
    a = b = c = 0xdeadbeef + ((uint32_t)length) + initval;

    /*--------------- all but the last block: affect some 32 bits of (a,b,c) */
    while (length > 12) {
        a += k[0];
        a += ((uint32_t)k[1]) << 8;
        a += ((uint32_t)k[2]) << 16;
        a += ((uint32_t)k[3]) << 24;
        b += k[4];
        b += ((uint32_t)k[5]) << 8;
        b += ((uint32_t)k[6]) << 16;
        b += ((uint32_t)k[7]) << 24;
        c += k[8];
        c += ((uint32_t)k[9]) << 8;
        c += ((uint32_t)k[10]) << 16;
        c += ((uint32_t)k[11]) << 24;
        H5_lookup3_mix(a, b, c);
        length -= 12;
        k += 12;
    }

    /*-------------------------------- last block: affect all 32 bits of (c) */
    switch (length) /* all the case statements fall through */
    {
        case 12:
            c += ((uint32_t)k[11]) << 24;
            /* FALLTHROUGH */
            H5_ATTR_FALLTHROUGH
        case 11:
            c += ((uint32_t)k[10]) << 16;
            /* FALLTHROUGH */
            H5_ATTR_FALLTHROUGH
        case 10:
            c += ((uint32_t)k[9]) << 8;
            /* FALLTHROUGH */
            H5_ATTR_FALLTHROUGH
        case 9:
            c += k[8];
            /* FALLTHROUGH */
            H5_ATTR_FALLTHROUGH
        case 8:
            b += ((uint32_t)k[7]) << 24;
            /* FALLTHROUGH */
            H5_ATTR_FALLTHROUGH
        case 7:
            b += ((uint32_t)k[6]) << 16;
            /* FALLTHROUGH */
            H5_ATTR_FALLTHROUGH
        case 6:
            b += ((uint32_t)k[5]) << 8;
            /* FALLTHROUGH */
            H5_ATTR_FALLTHROUGH
        case 5:
            b += k[4];
            /* FALLTHROUGH */
            H5_ATTR_FALLTHROUGH
        case 4:
            a += ((uint32_t)k[3]) << 24;
            /* FALLTHROUGH */
            H5_ATTR_FALLTHROUGH
        case 3:
            a += ((uint32_t)k[2]) << 16;
            /* FALLTHROUGH */
            H5_ATTR_FALLTHROUGH
        case 2:
            a += ((uint32_t)k[1]) << 8;
            /* FALLTHROUGH */
            H5_ATTR_FALLTHROUGH
        case 1:
            a += k[0];
            break;
        case 0:
            goto done;
        default:
            assert(0 && "This Should never be executed!");
    }

    H5_lookup3_final(a, b, c);

done:
    FUNC_LEAVE_NOAPI(c)
} /* end H5_checksum_lookup3() */

/*-------------------------------------------------------------------------
 * Function:  H5_checksum_metadata
 *
 * Purpose: Provide a more abstract routine for checksumming metadata
 *              in a file, where the policy of which algorithm to choose
 *              is centralized.
 *
 * Return:  checksum of input buffer (can't fail)
 *
 *-------------------------------------------------------------------------
 */
uint32_t
H5_checksum_metadata(const void *data, size_t len, uint32_t initval)
{
    FUNC_ENTER_NOAPI_NOINIT_NOERR

    /* Sanity check */
    assert(data);
    assert(len > 0);

    /* Choose the appropriate checksum routine */
    /* (use Bob Jenkin's "lookup3" algorithm for all buffer sizes) */
    FUNC_LEAVE_NOAPI(H5_checksum_lookup3(data, len, initval))
} /* end H5_checksum_metadata() */

/*-------------------------------------------------------------------------
 * Function:  H5_hash_string
 *
 * Purpose: Provide a simple & fast routine for hashing strings
 *
 * Note:        This algorithm is the 'djb2' algorithm described on this page:
 *              http://www.cse.yorku.ca/~oz/hash.html
 *
 * Return:  hash of input string (can't fail)
 *
 *-------------------------------------------------------------------------
 */
uint32_t
H5_hash_string(const char *str)
{
    uint32_t hash = 5381;
    int      c;

    FUNC_ENTER_NOAPI_NOINIT_NOERR

    /* Sanity check */
    assert(str);

    while ((c = *str++))
        hash = ((hash << 5) + hash) + (uint32_t)c; /* hash * 33 + c */

    FUNC_LEAVE_NOAPI(hash)
} /* end H5_hash_string() */

Coverage Report

Created: 2025-10-10 06:41

Line	Count	Source
1		/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
2		* Copyright by The HDF Group. *
3		* All rights reserved. *
4		* *
5		* This file is part of HDF5. The full HDF5 copyright notice, including *
6		* terms governing use, modification, and redistribution, is contained in *
7		* the LICENSE file, which can be found at the root of the source code *
8		* distribution tree, or in https://www.hdfgroup.org/licenses. *
9		* If you do not have access to either file, you may request a copy from *
10		* help@hdfgroup.org. *
11		* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
12
13		/*-------------------------------------------------------------------------
14		*
15		* Created: H5checksum.c
16		*
17		* Purpose: Internal code for computing fletcher32 checksums
18		*
19		*-------------------------------------------------------------------------
20		*/
21
22		/****************/
23		/* Module Setup */
24		/****************/
25		#include "H5module.h" /* This source code file is part of the H5 module */
26
27		/***********/
28		/* Headers */
29		/***********/
30		#include "H5private.h" /* Generic Functions */
31
32		/****************/
33		/* Local Macros */
34		/****************/
35
36		/* Polynomial quotient */
37		/* (same as the IEEE 802.3 (Ethernet) quotient) */
38	0	#define H5_CRC_QUOTIENT 0x04C11DB7
39
40		/******************/
41		/* Local Typedefs */
42		/******************/
43
44		/********************/
45		/* Package Typedefs */
46		/********************/
47
48		/********************/
49		/* Local Prototypes */
50		/********************/
51
52		/*********************/
53		/* Package Variables */
54		/*********************/
55
56		/*****************************/
57		/* Library Private Variables */
58		/*****************************/
59
60		/*******************/
61		/* Local Variables */
62		/*******************/
63
64		/* Table of CRCs of all 8-bit messages. */
65		static uint32_t H5_crc_table[256];
66
67		/* Flag: has the table been computed? */
68		static bool H5_crc_table_computed = false;
69
70		/*-------------------------------------------------------------------------
71		* Function: H5_checksum_fletcher32
72		*
73		* Purpose: This routine provides a generic, fast checksum algorithm for
74		* use in the library.
75		*
76		* Note: See the Wikipedia page for Fletcher's checksum:
77		* http://en.wikipedia.org/wiki/Fletcher%27s_checksum
78		* for more details, etc.
79		*
80		* Note #2: Per the information in RFC 3309:
81		* (http://tools.ietf.org/html/rfc3309)
82		* Fletcher's checksum is not reliable for small buffers.
83		*
84		* Note #3: The algorithm below differs from that given in the Wikipedia
85		* page by copying the data into 'sum1' in a more portable way
86		* and also by initializing 'sum1' and 'sum2' to 0 instead of
87		* 0xffff (for backward compatibility reasons with earlier
88		* HDF5 fletcher32 I/O filter routine, mostly).
89		*
90		* Return: 32-bit fletcher checksum of input buffer (can't fail)
91		*
92		*-------------------------------------------------------------------------
93		*/
94		uint32_t
95		H5_checksum_fletcher32(const void *_data, size_t _len)
96	0	{
97	0	const uint8_t data = (const uint8_t )_data; /* Pointer to the data to be summed */
98	0	size_t len = _len / 2; /* Length in 16-bit words */
99	0	uint32_t sum1 = 0, sum2 = 0;
100
101	0	FUNC_ENTER_NOAPI_NOINIT_NOERR
102
103		/* Sanity check */
104	0	assert(_data);
105	0	assert(_len > 0);
106
107		/* Compute checksum for pairs of bytes */
108		/* (the magic "360" value is the largest number of sums that can be
109		* performed without numeric overflow)
110		*/
111	0	while (len) {
112	0	size_t tlen = len > 360 ? 360 : len;
113	0	len -= tlen;
114	0	do {
115	0	sum1 += (uint32_t)(((uint16_t)data[0]) << 8) \| ((uint16_t)data[1]);
116	0	data += 2;
117	0	sum2 += sum1;
118	0	} while (--tlen);
119	0	sum1 = (sum1 & 0xffff) + (sum1 >> 16);
120	0	sum2 = (sum2 & 0xffff) + (sum2 >> 16);
121	0	}
122
123		/* Check for odd # of bytes */
124	0	if (_len % 2) {
125	0	sum1 += (uint32_t)(((uint16_t)*data) << 8);
126	0	sum2 += sum1;
127	0	sum1 = (sum1 & 0xffff) + (sum1 >> 16);
128	0	sum2 = (sum2 & 0xffff) + (sum2 >> 16);
129	0	} /* end if */
130
131		/* Second reduction step to reduce sums to 16 bits */
132	0	sum1 = (sum1 & 0xffff) + (sum1 >> 16);
133	0	sum2 = (sum2 & 0xffff) + (sum2 >> 16);
134
135	0	FUNC_LEAVE_NOAPI((sum2 << 16) \| sum1)
136	0	} /* end H5_checksum_fletcher32() */
137
138		/*-------------------------------------------------------------------------
139		* Function: H5__checksum_crc_make_table
140		*
141		* Purpose: Compute the CRC table for the CRC checksum algorithm
142		*
143		* Return: none
144		*
145		*-------------------------------------------------------------------------
146		*/
147		static void
148		H5__checksum_crc_make_table(void)
149	0	{
150	0	uint32_t c; /* Checksum for each byte value */
151	0	unsigned n, k; /* Local index variables */
152
153	0	FUNC_ENTER_PACKAGE_NOERR
154
155		/* Compute the checksum for each possible byte value */
156	0	for (n = 0; n < 256; n++) {
157	0	c = (uint32_t)n;
158	0	for (k = 0; k < 8; k++)
159	0	if (c & 1)
160	0	c = H5_CRC_QUOTIENT ^ (c >> 1);
161	0	else
162	0	c = c >> 1;
163	0	H5_crc_table[n] = c;
164	0	}
165	0	H5_crc_table_computed = true;
166
167	0	FUNC_LEAVE_NOAPI_VOID
168	0	} /* end H5__checksum_crc_make_table() */
169
170		/*-------------------------------------------------------------------------
171		* Function: H5__checksum_crc_update
172		*
173		* Purpose: Update a running CRC with the bytes buf[0..len-1]--the CRC
174		* should be initialized to all 1's, and the transmitted value
175		* is the 1's complement of the final running CRC (see the
176		* H5_checksum_crc() routine below)).
177		*
178		* Return: 32-bit CRC checksum of input buffer (can't fail)
179		*
180		*-------------------------------------------------------------------------
181		*/
182		static uint32_t
183		H5__checksum_crc_update(uint32_t crc, const uint8_t *buf, size_t len)
184	0	{
185	0	size_t n; /* Local index variable */
186
187	0	FUNC_ENTER_PACKAGE_NOERR
188
189		/* Initialize the CRC table if necessary */
190	0	if (!H5_crc_table_computed)
191	0	H5__checksum_crc_make_table();
192
193		/* Update the CRC with the results from this buffer */
194	0	for (n = 0; n < len; n++)
195	0	crc = H5_crc_table[(crc ^ buf[n]) & 0xff] ^ (crc >> 8);
196
197	0	FUNC_LEAVE_NOAPI(crc)
198	0	} /* end H5__checksum_crc_update() */
199
200		/*-------------------------------------------------------------------------
201		* Function: H5_checksum_crc
202		*
203		* Purpose: This routine provides a generic checksum algorithm for
204		* use in the library.
205		*
206		* Note: This algorithm was based on the implementation described
207		* in the document describing the PNG image format:
208		* http://www.w3.org/TR/PNG/#D-CRCAppendix
209		*
210		* Return: 32-bit CRC checksum of input buffer (can't fail)
211		*
212		*-------------------------------------------------------------------------
213		*/
214		uint32_t
215		H5_checksum_crc(const void *_data, size_t len)
216	0	{
217	0	FUNC_ENTER_NOAPI_NOINIT_NOERR
218
219		/* Sanity check */
220	0	assert(_data);
221	0	assert(len > 0);
222
223	0	FUNC_LEAVE_NOAPI(H5__checksum_crc_update((uint32_t)0xffffffffL, (const uint8_t *)_data, len) ^
224	0	0xffffffffL)
225	0	} /* end H5_checksum_crc() */
226
227		/*
228		-------------------------------------------------------------------------------
229		H5_lookup3_mix -- mix 3 32-bit values reversibly.
230
231		This is reversible, so any information in (a,b,c) before mix() is
232		still in (a,b,c) after mix().
233
234		If four pairs of (a,b,c) inputs are run through mix(), or through
235		mix() in reverse, there are at least 32 bits of the output that
236		are sometimes the same for one pair and different for another pair.
237		This was tested for:
238		* pairs that differed by one bit, by two bits, in any combination
239		of top bits of (a,b,c), or in any combination of bottom bits of
240		(a,b,c).
241		* "differ" is defined as +, -, ^, or ~^. For + and -, I transformed
242		the output delta to a Gray code (a^(a>>1)) so a string of 1's (as
243		is commonly produced by subtraction) look like a single 1-bit
244		difference.
245		* the base values were pseudorandom, all zero but one bit set, or
246		all zero plus a counter that starts at zero.
247
248		Some k values for my "a-=c; a^=rot(c,k); c+=b;" arrangement that
249		satisfy this are
250		4 6 8 16 19 4
251		9 15 3 18 27 15
252		14 9 3 7 17 3
253		Well, "9 15 3 18 27 15" didn't quite get 32 bits diffing
254		for "differ" defined as + with a one-bit base and a two-bit delta. I
255		used http://burtleburtle.net/bob/hash/avalanche.html to choose
256		the operations, constants, and arrangements of the variables.
257
258		This does not achieve avalanche. There are input bits of (a,b,c)
259		that fail to affect some output bits of (a,b,c), especially of a. The
260		most thoroughly mixed value is c, but it doesn't really even achieve
261		avalanche in c.
262
263		This allows some parallelism. Read-after-writes are good at doubling
264		the number of bits affected, so the goal of mixing pulls in the opposite
265		direction as the goal of parallelism. I did what I could. Rotates
266		seem to cost as much as shifts on every machine I could lay my hands
267		on, and rotates are much kinder to the top and bottom bits, so I used
268		rotates.
269		-------------------------------------------------------------------------------
270		*/
271	75.3k	#define H5_lookup3_rot(x, k) (((x) << (k)) ^ ((x) >> (32 - (k))))
272		#define H5_lookup3_mix(a, b, c) \
273	10.1k	do { \
274	10.1k	a -= c; \
275	10.1k	a ^= H5_lookup3_rot(c, 4); \
276	10.1k	c += b; \
277	10.1k	b -= a; \
278	10.1k	b ^= H5_lookup3_rot(a, 6); \
279	10.1k	a += c; \
280	10.1k	c -= b; \
281	10.1k	c ^= H5_lookup3_rot(b, 8); \
282	10.1k	b += a; \
283	10.1k	a -= c; \
284	10.1k	a ^= H5_lookup3_rot(c, 16); \
285	10.1k	c += b; \
286	10.1k	b -= a; \
287	10.1k	b ^= H5_lookup3_rot(a, 19); \
288	10.1k	a += c; \
289	10.1k	c -= b; \
290	10.1k	c ^= H5_lookup3_rot(b, 4); \
291	10.1k	b += a; \
292	10.1k	} while (0)
293
294		/*
295		-------------------------------------------------------------------------------
296		H5_lookup3_final -- final mixing of 3 32-bit values (a,b,c) into c
297
298		Pairs of (a,b,c) values differing in only a few bits will usually
299		produce values of c that look totally different. This was tested for
300		* pairs that differed by one bit, by two bits, in any combination
301		of top bits of (a,b,c), or in any combination of bottom bits of
302		(a,b,c).
303		* "differ" is defined as +, -, ^, or ~^. For + and -, I transformed
304		the output delta to a Gray code (a^(a>>1)) so a string of 1's (as
305		is commonly produced by subtraction) look like a single 1-bit
306		difference.
307		* the base values were pseudorandom, all zero but one bit set, or
308		all zero plus a counter that starts at zero.
309
310		These constants passed:
311		14 11 25 16 4 14 24
312		12 14 25 16 4 14 24
313		and these came close:
314		4 8 15 26 3 22 24
315		10 8 15 26 3 22 24
316		11 8 15 26 3 22 24
317		-------------------------------------------------------------------------------
318		*/
319		#define H5_lookup3_final(a, b, c) \
320	2.08k	do { \
321	2.08k	c ^= b; \
322	2.08k	c -= H5_lookup3_rot(b, 14); \
323	2.08k	a ^= c; \
324	2.08k	a -= H5_lookup3_rot(c, 11); \
325	2.08k	b ^= a; \
326	2.08k	b -= H5_lookup3_rot(a, 25); \
327	2.08k	c ^= b; \
328	2.08k	c -= H5_lookup3_rot(b, 16); \
329	2.08k	a ^= c; \
330	2.08k	a -= H5_lookup3_rot(c, 4); \
331	2.08k	b ^= a; \
332	2.08k	b -= H5_lookup3_rot(a, 14); \
333	2.08k	c ^= b; \
334	2.08k	c -= H5_lookup3_rot(b, 24); \
335	2.08k	} while (0)
336
337		/*
338		-------------------------------------------------------------------------------
339		H5_checksum_lookup3() -- hash a variable-length key into a 32-bit value
340		k : the key (the unaligned variable-length array of bytes)
341		length : the length of the key, counting by bytes
342		initval : can be any 4-byte value
343		Returns a 32-bit value. Every bit of the key affects every bit of
344		the return value. Two keys differing by one or two bits will have
345		totally different hash values.
346
347		The best hash table sizes are powers of 2. There is no need to do
348		mod a prime (mod is so slow!). If you need less than 32 bits,
349		use a bitmask. For example, if you need only 10 bits, do
350		h = (h & hashmask(10));
351		In which case, the hash table should have hashsize(10) elements.
352
353		If you are hashing n strings (uint8_t **)k, do it like this:
354		for (i=0, h=0; i<n; ++i) h = H5_checksum_lookup( k[i], len[i], h);
355
356		By Bob Jenkins, 2006. bob_jenkins@burtleburtle.net. You may use this
357		code any way you wish, private, educational, or commercial. It's free.
358
359		Use for hash table lookup, or anything where one collision in 2^^32 is
360		acceptable. Do NOT use for cryptographic purposes.
361		-------------------------------------------------------------------------------
362		*/
363
364		uint32_t
365		H5_checksum_lookup3(const void *key, size_t length, uint32_t initval)
366	2.08k	{
367	2.08k	const uint8_t k = (const uint8_t )key;
368	2.08k	uint32_t a, b, c = 0; /* internal state */
369
370	2.08k	FUNC_ENTER_NOAPI_NOINIT_NOERR
371
372		/* Sanity check */
373	2.08k	assert(key);
374	2.08k	assert(length > 0);
375
376		/* Set up the internal state */
377	2.08k	a = b = c = 0xdeadbeef + ((uint32_t)length) + initval;
378
379		/--------------- all but the last block: affect some 32 bits of (a,b,c) /
380	12.2k	while (length > 12) {
381	10.1k	a += k[0];
382	10.1k	a += ((uint32_t)k[1]) << 8;
383	10.1k	a += ((uint32_t)k[2]) << 16;
384	10.1k	a += ((uint32_t)k[3]) << 24;
385	10.1k	b += k[4];
386	10.1k	b += ((uint32_t)k[5]) << 8;
387	10.1k	b += ((uint32_t)k[6]) << 16;
388	10.1k	b += ((uint32_t)k[7]) << 24;
389	10.1k	c += k[8];
390	10.1k	c += ((uint32_t)k[9]) << 8;
391	10.1k	c += ((uint32_t)k[10]) << 16;
392	10.1k	c += ((uint32_t)k[11]) << 24;
393	10.1k	H5_lookup3_mix(a, b, c);
394	10.1k	length -= 12;
395	10.1k	k += 12;
396	10.1k	}
397
398		/-------------------------------- last block: affect all 32 bits of (c) /
399	2.08k	switch (length) /* all the case statements fall through */
400	2.08k	{
401	16	case 12:
402	16	c += ((uint32_t)k[11]) << 24;
403		/* FALLTHROUGH */
404	16	H5_ATTR_FALLTHROUGH
405	54	case 11:
406	54	c += ((uint32_t)k[10]) << 16;
407		/* FALLTHROUGH */
408	54	H5_ATTR_FALLTHROUGH
409	89	case 10:
410	89	c += ((uint32_t)k[9]) << 8;
411		/* FALLTHROUGH */
412	89	H5_ATTR_FALLTHROUGH
413	157	case 9:
414	157	c += k[8];
415		/* FALLTHROUGH */
416	157	H5_ATTR_FALLTHROUGH
417	1.77k	case 8:
418	1.77k	b += ((uint32_t)k[7]) << 24;
419		/* FALLTHROUGH */
420	1.77k	H5_ATTR_FALLTHROUGH
421	1.89k	case 7:
422	1.89k	b += ((uint32_t)k[6]) << 16;
423		/* FALLTHROUGH */
424	1.89k	H5_ATTR_FALLTHROUGH
425	2.01k	case 6:
426	2.01k	b += ((uint32_t)k[5]) << 8;
427		/* FALLTHROUGH */
428	2.01k	H5_ATTR_FALLTHROUGH
429	2.01k	case 5:
430	2.01k	b += k[4];
431		/* FALLTHROUGH */
432	2.01k	H5_ATTR_FALLTHROUGH
433	2.04k	case 4:
434	2.04k	a += ((uint32_t)k[3]) << 24;
435		/* FALLTHROUGH */
436	2.04k	H5_ATTR_FALLTHROUGH
437	2.07k	case 3:
438	2.07k	a += ((uint32_t)k[2]) << 16;
439		/* FALLTHROUGH */
440	2.07k	H5_ATTR_FALLTHROUGH
441	2.07k	case 2:
442	2.07k	a += ((uint32_t)k[1]) << 8;
443		/* FALLTHROUGH */
444	2.07k	H5_ATTR_FALLTHROUGH
445	2.08k	case 1:
446	2.08k	a += k[0];
447	2.08k	break;
448	0	case 0:
449	0	goto done;
450	0	default:
451	0	assert(0 && "This Should never be executed!");
452	2.08k	}
453
454	2.08k	H5_lookup3_final(a, b, c);
455
456	2.08k	done:
457	2.08k	FUNC_LEAVE_NOAPI(c)
458	2.08k	} /* end H5_checksum_lookup3() */
459
460		/*-------------------------------------------------------------------------
461		* Function: H5_checksum_metadata
462		*
463		* Purpose: Provide a more abstract routine for checksumming metadata
464		* in a file, where the policy of which algorithm to choose
465		* is centralized.
466		*
467		* Return: checksum of input buffer (can't fail)
468		*
469		*-------------------------------------------------------------------------
470		*/
471		uint32_t
472		H5_checksum_metadata(const void *data, size_t len, uint32_t initval)
473	2.08k	{
474	2.08k	FUNC_ENTER_NOAPI_NOINIT_NOERR
475
476		/* Sanity check */
477	2.08k	assert(data);
478	2.08k	assert(len > 0);
479
480		/* Choose the appropriate checksum routine */
481		/* (use Bob Jenkin's "lookup3" algorithm for all buffer sizes) */
482	2.08k	FUNC_LEAVE_NOAPI(H5_checksum_lookup3(data, len, initval))
483	2.08k	} /* end H5_checksum_metadata() */
484
485		/*-------------------------------------------------------------------------
486		* Function: H5_hash_string
487		*
488		* Purpose: Provide a simple & fast routine for hashing strings
489		*
490		* Note: This algorithm is the 'djb2' algorithm described on this page:
491		* http://www.cse.yorku.ca/~oz/hash.html
492		*
493		* Return: hash of input string (can't fail)
494		*
495		*-------------------------------------------------------------------------
496		*/
497		uint32_t
498		H5_hash_string(const char *str)
499	492k	{
500	492k	uint32_t hash = 5381;
501	492k	int c;
502
503	492k	FUNC_ENTER_NOAPI_NOINIT_NOERR
504
505		/* Sanity check */
506	492k	assert(str);
507
508	7.46M	while ((c = *str++))
509	6.97M	hash = ((hash << 5) + hash) + (uint32_t)c; /* hash * 33 + c */
510
511	492k	FUNC_LEAVE_NOAPI(hash)
512	492k	} /* end H5_hash_string() */