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Re: svn commit: r1333326 - in /subversion/trunk/subversion: include/private/svn_hash_private.h libsvn_fs_fs/temp_serializer.c libsvn_subr/hash.c

From: Stefan Fuhrmann <eqfox_at_web.de>
Date: Sun, 06 May 2012 00:23:33 +0200

Hyrum K Wright wrote:
> On Thu, May 3, 2012 at 2:16 AM,<stefan2_at_apache.org> wrote:
>> Author: stefan2
>> Date: Thu May 3 07:16:11 2012
>> New Revision: 1333326
>>
>> URL:http://svn.apache.org/viewvc?rev=1333326&view=rev
>> Log:
>> Introduce private API functions that wrap apr_hash_make_custom
>> and return hash tables that are 2 to 4 times faster than the APR default.
>> Both yield repeatable results (each instance will store items in the same
>> order if the keys are the same). The first, svn_hask__make will return
>> a hash table that behaves like pre APR 1.4.6 default hashes.
>>
>> * subversion/include/private/svn_hash_private.h
>> (svn_hash__make, svn_hash__make_fast): new private API
>> * subversion/libsvn_subr/hash.c
>> (svn_hash_from_cstring_keys): use new API
>> (hashfunc_compatible, LOWER_7BITS_SET, BIT_7_SET, READ_CHUNK,
>> hashfunc_fast): implement efficient hash functions
>> (svn_hash__make, svn_hash__make_fast): implement new private API
>> * subversion/libsvn_fs_fs/temp_serializer.c
>> (deserialize_dir, svn_fs_fs__deserialize_properties): use new API
>>
>> Modified:
>> subversion/trunk/subversion/include/private/svn_hash_private.h
>> subversion/trunk/subversion/libsvn_fs_fs/temp_serializer.c
>> subversion/trunk/subversion/libsvn_subr/hash.c
>>
>> Modified: subversion/trunk/subversion/include/private/svn_hash_private.h
>> URL:http://svn.apache.org/viewvc/subversion/trunk/subversion/include/private/svn_hash_private.h?rev=1333326&r1=1333325&r2=1333326&view=diff
>> ==============================================================================
>> --- subversion/trunk/subversion/include/private/svn_hash_private.h (original)
>> +++ subversion/trunk/subversion/include/private/svn_hash_private.h Thu May 3 07:16:11 2012
>> @@ -102,6 +102,31 @@ svn_hash__get_bool(apr_hash_t *hash,
>>
>> /** @} */
>>
>> +/**
>> + * @defgroup svn_hash_create Create optimized APR hash tables
>> + * @{
>> + */
>> +
>> +/** Returns a hash table, allocated in @a pool, with the same ordering of
>> + * elements as APR 1.4.5 or earlier (using apr_hashfunc_default) but uses
>> + * a faster hash function implementation.
>> + *
>> + * @since New in 1.8.
>> + */
>> +apr_hash_t *
>> +svn_hash__make(apr_pool_t *pool);
>> +
>> +/** Returns a hash table, allocated in @a pool, that is faster to modify
>> + * and access then the ones returned by @ref svn_hash__make. The element
>> + * order does not match any APR default.
>> + *
>> + * @since New in 1.8.
>> + */
>> +apr_hash_t *
>> +svn_hash__make_fast(apr_pool_t *pool);
>> +
>> +/** @} */
>> +
>> /** @} */
>>
>> #ifdef __cplusplus
>>
>> Modified: subversion/trunk/subversion/libsvn_fs_fs/temp_serializer.c
>> URL:http://svn.apache.org/viewvc/subversion/trunk/subversion/libsvn_fs_fs/temp_serializer.c?rev=1333326&r1=1333325&r2=1333326&view=diff
>> ==============================================================================
>> --- subversion/trunk/subversion/libsvn_fs_fs/temp_serializer.c (original)
>> +++ subversion/trunk/subversion/libsvn_fs_fs/temp_serializer.c Thu May 3 07:16:11 2012
>> @@ -30,6 +30,7 @@
>>
>> #include "private/svn_fs_util.h"
>> #include "private/svn_temp_serializer.h"
>> +#include "private/svn_hash_private.h"
>>
>> #include "temp_serializer.h"
>>
>> @@ -359,7 +360,7 @@ serialize_dir(apr_hash_t *entries, apr_p
>> static apr_hash_t *
>> deserialize_dir(void *buffer, hash_data_t *hash_data, apr_pool_t *pool)
>> {
>> - apr_hash_t *result = apr_hash_make(pool);
>> + apr_hash_t *result = svn_hash__make(pool);
>> apr_size_t i;
>> apr_size_t count;
>> svn_fs_dirent_t *entry;
>> @@ -678,7 +679,7 @@ svn_fs_fs__deserialize_properties(void *
>> apr_size_t data_len,
>> apr_pool_t *pool)
>> {
>> - apr_hash_t *hash = apr_hash_make(pool);
>> + apr_hash_t *hash = svn_hash__make(pool);
>> properties_data_t *properties = (properties_data_t *)data;
>> size_t i;
>>
>>
>> Modified: subversion/trunk/subversion/libsvn_subr/hash.c
>> URL:http://svn.apache.org/viewvc/subversion/trunk/subversion/libsvn_subr/hash.c?rev=1333326&r1=1333325&r2=1333326&view=diff
>> ==============================================================================
>> --- subversion/trunk/subversion/libsvn_subr/hash.c (original)
>> +++ subversion/trunk/subversion/libsvn_subr/hash.c Thu May 3 07:16:11 2012
>> @@ -40,6 +40,7 @@
>> #include "svn_pools.h"
>>
>> #include "private/svn_dep_compat.h"
>> +#include "private/svn_string_private.h"
>> #include "private/svn_hash_private.h"
>>
>> #include "svn_private_config.h"
>> @@ -496,7 +497,7 @@ svn_hash_from_cstring_keys(apr_hash_t **
>> apr_pool_t *pool)
>> {
>> int i;
>> - apr_hash_t *hash = apr_hash_make(pool);
>> + apr_hash_t *hash = svn_hash__make(pool);
>> for (i = 0; i< keys->nelts; i++)
>> {
>> const char *key =
>> @@ -561,3 +562,127 @@ svn_hash__get_bool(apr_hash_t *hash, con
>> return default_value;
>> }
>>
>> +
>> +
>> +/*** Optimized hash functions ***/
>> +
>> +/* Optimized version of apr_hashfunc_default. It assumes that the CPU has
>> + * 32-bit multiplications with high throughput of at least 1 operation
>> + * every 3 cycles. Latency is not an issue. Another optimization is a
>> + * mildly unrolled main loop.
>> + */
>> +static unsigned int
>> +hashfunc_compatible(const char *char_key, apr_ssize_t *klen)
>> +{
>> + unsigned int hash = 0;
>> + const unsigned char *key = (const unsigned char *)char_key;
>> + const unsigned char *p;
>> + apr_ssize_t i;
>> +
>> + if (*klen == APR_HASH_KEY_STRING)
>> + {
>> + for (p = key; ; p+=4)
>> + {
>> + unsigned int new_hash = hash * 33 * 33 * 33 * 33;
>> + if (!p[0]) break;
>> + new_hash += p[0] * 33 * 33 * 33;
>> + if (!p[1]) break;
>> + new_hash += p[1] * 33 * 33;
>> + if (!p[2]) break;
>> + new_hash += p[2] * 33;
>> + if (!p[3]) break;
>> + hash = new_hash + p[3];
>> + }
>> + for (; *p; p++)
>> + hash = hash * 33 + *p;
>> +
>> + *klen = p - key;
>> + }
>> + else
>> + {
>> + for (p = key, i = *klen; i>= 4; i-=4, p+=4)
>> + {
>> + hash = hash * 33 * 33 * 33 * 33
>> + + p[0] * 33 * 33 * 33
>> + + p[1] * 33 * 33
>> + + p[2] * 33
>> + + p[3];
>> + }
>> + for (; i; i--, p++)
>> + hash = hash * 33 + *p;
>> + }
>> +
>> + return hash;
>> +}
>> +
>> +#define LOWER_7BITS_SET 0x7f7f7f7f
>> +#define BIT_7_SET 0x80808080
>> +
>> +#if SVN_UNALIGNED_ACCESS_IS_OK
>> +# define READ_CHUNK(p)\
>> + *(const apr_uint32_t *)(p);
>> +#else
>> +# define READ_CHUNK(p) \
>> + ( (apr_uint32_t)p[0] \
>> + + ((apr_uint32_t)p[1]<< 8) \
>> + + ((apr_uint32_t)p[2]<< 16) \
>> + + ((apr_uint32_t)p[3]<< 24))
>> +#endif
>> +
>> +/* Similar to the previous but operates on 4 bytes at once instead of the
>> + * classic unroll. This is particularly fast when unaligned access is
>> + * supported.
>> + */
>> +static unsigned int
>> +hashfunc_fast(const char *char_key, apr_ssize_t *klen)
>> +{
>> + unsigned int hash = 0;
>> + const unsigned char *key = (const unsigned char *)char_key;
>> + const unsigned char *p;
>> + apr_ssize_t i;
>> + apr_uint32_t chunk, test;
>> +
>> + if (*klen == APR_HASH_KEY_STRING)
>> + {
>> + for (p = key; ; p += sizeof(chunk))
>> + {
>> + /* This is a variant of the well-known strlen test: */
>> + chunk = READ_CHUNK(p);
>> + test = chunk | ((chunk& LOWER_7BITS_SET) + LOWER_7BITS_SET);
>> + if ((test& BIT_7_SET) != BIT_7_SET)
>> + break;
>> +
>> + hash = (hash + chunk) * 0xd1f3da69;
>> + }
>> + for (; i; i--, p++)
> i is being used uninitialized here, giving potential bogus results.
>
> -Hyrum
>
Yup. I've already stumbled across that one when I ran
some benchmarks for Philip. Fixed in r1333779.

-- Stefan^2.
Received on 2012-05-06 02:24:07 CEST

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