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

From: Hyrum K Wright <hyrum_at_hyrumwright.org>
Date: Sat, 1 Jan 2011 12:14:13 -0500

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.

> +
> +    /* 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 18:14:55 CET

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