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[svn-r12661] Description:
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    Add 'loookup3' checksum routine and switch to using it for metadata
checksums - it's just as "strong" as the CRC32 and about 40% faster in general
(with some compiler optimizations, it's nearly as fast as the fletcher-32
algorithm).

Tested on:
    Linux/32 2.6 (chicago)
    Linux/64 2.6 (chicago2)
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@qkoziol
qkoziol committed Sep 12, 2006
1 parent 314b3f5 commit d3a12e1
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Showing 3 changed files with 213 additions and 10 deletions.
192 changes: 182 additions & 10 deletions src/H5checksum.c
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Original file line number Diff line number Diff line change
Expand Up @@ -97,7 +97,8 @@ static hbool_t H5_crc_table_computed = FALSE;
* 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, mostly).
* 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)
*
Expand Down Expand Up @@ -250,6 +251,184 @@ H5_checksum_crc(const void *_data, size_t len)
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) \
{ \
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; \
}

/*
-------------------------------------------------------------------------------
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) \
{ \
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); \
}

/*
-------------------------------------------------------------------------------
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 sooo 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 = hashlittle( 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; /* internal state */

FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5_checksum_lookup3)

/* Sanity check */
HDassert(key);
HDassert(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;
case 11: c+=((uint32_t)k[10])<<16;
case 10: c+=((uint32_t)k[9])<<8;
case 9 : c+=k[8];
case 8 : b+=((uint32_t)k[7])<<24;
case 7 : b+=((uint32_t)k[6])<<16;
case 6 : b+=((uint32_t)k[5])<<8;
case 5 : b+=k[4];
case 4 : a+=((uint32_t)k[3])<<24;
case 3 : a+=((uint32_t)k[2])<<16;
case 2 : a+=((uint32_t)k[1])<<8;
case 1 : a+=k[0];
break;
case 0 : goto done;
}

H5_lookup3_final(a, b, c);

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


/*-------------------------------------------------------------------------
* Function: H5_checksum_metadata
Expand All @@ -268,21 +447,14 @@ H5_checksum_crc(const void *_data, size_t len)
uint32_t
H5_checksum_metadata(const void *data, size_t len)
{
uint32_t chksum; /* Checksum value to return */

FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5_checksum_metadata)

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

/* Choose the appropriate checksum routine */
/* (use Fletcher's checksum for "larger" buffers and CRC for "shorter" ones) */
if(len < 256)
chksum = H5_checksum_crc(data, len);
else
chksum = H5_checksum_fletcher32(data, len);

FUNC_LEAVE_NOAPI(chksum)
/* (use Bob Jenkin's "lookup3" algorithm for all buffer sizes) */
FUNC_LEAVE_NOAPI(H5_checksum_lookup3(data, len))
} /* end H5_checksum_metadata() */

1 change: 1 addition & 0 deletions src/H5private.h
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Original file line number Diff line number Diff line change
Expand Up @@ -1449,6 +1449,7 @@ H5_DLL int H5Z_term_interface(void);
/* Checksum functions */
H5_DLL uint32_t H5_checksum_fletcher32(const void *data, size_t len);
H5_DLL uint32_t H5_checksum_crc(const void *data, size_t len);
H5_DLL uint32_t H5_checksum_lookup3(const void *data, size_t len);
H5_DLL uint32_t H5_checksum_metadata(const void *data, size_t len);

/* Functions for debugging */
Expand Down
30 changes: 30 additions & 0 deletions test/tchecksum.c
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Original file line number Diff line number Diff line change
Expand Up @@ -57,13 +57,19 @@ test_chksum_size_one(void)
chksum = H5_checksum_crc(buf, sizeof(buf));
VERIFY(chksum, 0xfa2568b7, "H5_checksum_crc");

chksum = H5_checksum_lookup3(buf, sizeof(buf));
VERIFY(chksum, 0xa209c931, "H5_checksum_lookup3");

/* Buffer w/zero(s) for data */
HDmemset(buf, 0, sizeof(buf));
chksum = H5_checksum_fletcher32(buf, sizeof(buf));
VERIFY(chksum, 0, "H5_checksum_fletcher32");

chksum = H5_checksum_crc(buf, sizeof(buf));
VERIFY(chksum, 0xfa60fb57, "H5_checksum_crc");

chksum = H5_checksum_lookup3(buf, sizeof(buf));
VERIFY(chksum, 0x8ba9414b, "H5_checksum_lookup3");
} /* test_chksum_size_one() */


Expand All @@ -85,13 +91,19 @@ test_chksum_size_two(void)
chksum = H5_checksum_crc(buf, sizeof(buf));
VERIFY(chksum, 0xfc856608, "H5_checksum_crc");

chksum = H5_checksum_lookup3(buf, sizeof(buf));
VERIFY(chksum, 0x8ba7a6c9, "H5_checksum_lookup3");

/* Buffer w/zero(s) for data */
HDmemset(buf, 0, sizeof(buf));
chksum = H5_checksum_fletcher32(buf, sizeof(buf));
VERIFY(chksum, 0, "H5_checksum_fletcher32");

chksum = H5_checksum_crc(buf, sizeof(buf));
VERIFY(chksum, 0xfc7e9b20, "H5_checksum_crc");

chksum = H5_checksum_lookup3(buf, sizeof(buf));
VERIFY(chksum, 0x62cd61b3, "H5_checksum_lookup3");
} /* test_chksum_size_two() */


Expand All @@ -113,13 +125,19 @@ test_chksum_size_three(void)
chksum = H5_checksum_crc(buf, sizeof(buf));
VERIFY(chksum, 0xfebc5d70, "H5_checksum_crc");

chksum = H5_checksum_lookup3(buf, sizeof(buf));
VERIFY(chksum, 0xcebdf4f0, "H5_checksum_lookup3");

/* Buffer w/zero(s) for data */
HDmemset(buf, 0, sizeof(buf));
chksum = H5_checksum_fletcher32(buf, sizeof(buf));
VERIFY(chksum, 0, "H5_checksum_fletcher32");

chksum = H5_checksum_crc(buf, sizeof(buf));
VERIFY(chksum, 0xf9cc4c7a, "H5_checksum_crc");

chksum = H5_checksum_lookup3(buf, sizeof(buf));
VERIFY(chksum, 0x6bd0060f, "H5_checksum_lookup3");
} /* test_chksum_size_three() */


Expand All @@ -141,13 +159,19 @@ test_chksum_size_four(void)
chksum = H5_checksum_crc(buf, sizeof(buf));
VERIFY(chksum, 0xff398a46, "H5_checksum_crc");

chksum = H5_checksum_lookup3(buf, sizeof(buf));
VERIFY(chksum, 0x2c88bb51, "H5_checksum_lookup3");

/* Buffer w/zero(s) for data */
HDmemset(buf, 0, sizeof(buf));
chksum = H5_checksum_fletcher32(buf, sizeof(buf));
VERIFY(chksum, 0, "H5_checksum_fletcher32");

chksum = H5_checksum_crc(buf, sizeof(buf));
VERIFY(chksum, 0xff117081, "H5_checksum_crc");

chksum = H5_checksum_lookup3(buf, sizeof(buf));
VERIFY(chksum, 0x049396b8, "H5_checksum_lookup3");
} /* test_chksum_size_four() */


Expand All @@ -173,13 +197,19 @@ test_chksum_large(void)
chksum = H5_checksum_crc(large_buf, sizeof(large_buf));
VERIFY(chksum, 0xfbd0f7c0, "H5_checksum_crc");

chksum = H5_checksum_lookup3(large_buf, sizeof(large_buf));
VERIFY(chksum, 0x1bd2ee7b, "H5_checksum_lookup3");

/* Buffer w/zero(s) for data */
HDmemset(large_buf, 0, sizeof(large_buf));
chksum = H5_checksum_fletcher32(large_buf, sizeof(large_buf));
VERIFY(chksum, 0, "H5_checksum_fletcher32");

chksum = H5_checksum_crc(large_buf, sizeof(large_buf));
VERIFY(chksum, 0xfac8b4c4, "H5_checksum_crc");

chksum = H5_checksum_lookup3(large_buf, sizeof(large_buf));
VERIFY(chksum, 0x930c7afc, "H5_checksum_lookup3");
} /* test_chksum_large() */


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