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Re: svn commit: r1054250 - /subversion/trunk/subversion/libsvn_subr/eol.c

From: Stefan Fuhrmann <eqfox_at_web.de>
Date: Sat, 01 Jan 2011 23:30:14 +0100

On 01.01.2011 18:14, Hyrum K Wright wrote:
> On Sat, Jan 1, 2011 at 11:18 AM,<stefan2_at_apache.org> wrote:
>> Author: stefan2
>> Date: Sat Jan 1 16:18:55 2011
>> New Revision: 1054250
>>
>> URL: http://svn.apache.org/viewvc?rev=1054250&view=rev
>> Log:
>> About 3x speed up of svn_eol__find_eol_start() on 64 bit machines
>> (20 .. 40% on 32 bits). This function is a significant contributor
>> to our diff algorithm.
>>
>> * subversion/libsvn_subr/eol.c
>> (svn_eol__find_eol_start): use some masking magic to process
>> the data in larger chunks
>>
>> Modified:
>> subversion/trunk/subversion/libsvn_subr/eol.c
>>
>> Modified: subversion/trunk/subversion/libsvn_subr/eol.c
>> URL: http://svn.apache.org/viewvc/subversion/trunk/subversion/libsvn_subr/eol.c?rev=1054250&r1=1054249&r2=1054250&view=diff
>> ==============================================================================
>> --- subversion/trunk/subversion/libsvn_subr/eol.c (original)
>> +++ subversion/trunk/subversion/libsvn_subr/eol.c Sat Jan 1 16:18:55 2011
>> @@ -29,14 +29,68 @@
>> #include "svn_io.h"
>> #include "private/svn_eol_private.h"
>>
>> +/* Machine-word-sized masks used in svn_eol__find_eol_start.
>> + */
>> +#if APR_SIZEOF_VOIDP == 8
>> +# define LOWER_7BITS_SET 0x7f7f7f7f7f7f7f7f
>> +# define BIT_7_SET 0x8080808080808080
>> +# define R_MASK 0x0a0a0a0a0a0a0a0a
>> +# define N_MASK 0x0d0d0d0d0d0d0d0d
>> +#else
>> +# define LOWER_7BITS_SET 0x7f7f7f7f
>> +# define BIT_7_SET 0x80808080
>> +# define R_MASK 0x0a0a0a0a
>> +# define N_MASK 0x0d0d0d0d
>> +#endif
>> +
>> char *
>> svn_eol__find_eol_start(char *buf, apr_size_t len)
>> {
>> +#if !SVN_UNALIGNED_ACCESS_IS_OK
>> +
>> + /* On some systems, we need to make sure that buf is properly aligned
>> + * for chunky data access. This overhead is still justified because
>> + * only lines tend to be tens of chars long.
>> + */
>> + for (; (len> 0)&& ((apr_uintptr_t)buf)& (sizeof(apr_uintptr_t)-1)
>> + ; ++buf, --len)
>> + {
>> + if (*buf == '\n' || *buf == '\r')
>> + return buf;
>> + }
>> +
>> +#endif
>> +
>> + /* Scan the input one machine word at a time. */
>> + for (; len> sizeof(apr_uintptr_t)
>> + ; buf += sizeof(apr_uintptr_t), len -= sizeof(apr_uintptr_t))
>> + {
>> + /* This is a variant of the well-known strlen test: */
>> + apr_uintptr_t chunk = *(const apr_uintptr_t *)buf;
> This type isn't in APR 0.9.x, which is causing build failures on at
> least two of the build slaves.
>
Oops - sorry! This makes it absolute clear
what the @since clauses in our headers
are worth.

Should be fixed by r1054264.

-- Stefan^2.
>> +
>> + /* A byte in R_TEST is \0, iff it was \r in *BUF.
>> + * Similarly, N_TEST is an indicator for \n. */
>> + apr_uintptr_t r_test = chunk ^ R_MASK;
>> + apr_uintptr_t n_test = chunk ^ N_MASK;
>> +
>> + /* A byte in R_TEST can by< 0x80, iff it has been \0 before
>> + * (i.e. \r in *BUF). Dito for N_TEST. */
>> + r_test |= (r_test& LOWER_7BITS_SET) + LOWER_7BITS_SET;
>> + n_test |= (n_test& LOWER_7BITS_SET) + LOWER_7BITS_SET;
>> +
>> + /* Check whether at least one of the words contains a byte<0x80
>> + * (if one is detected, there was a \r or \n in CHUNK). */
>> + if ((r_test& n_test& BIT_7_SET) != BIT_7_SET)
>> + break;
>> + }
>> +
>> + /* The remaining odd bytes will be examined the naive way: */
>> for (; len> 0; ++buf, --len)
>> {
>> if (*buf == '\n' || *buf == '\r')
>> return buf;
>> }
>> +
>> return NULL;
>> }
>>
>>
>>
>>
Received on 2011-01-01 23:44:17 CET

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