skip_trailing.cc

/* Copyright (c) 2013, Oracle and/or its affiliates. All rights reserved.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; version 2 of the License.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA */

#include "skip_trailing.h"

namespace skip_trailing_space_unittest {

/* SPACE_INT is a word that contains only spaces */
#if SIZEOF_INT == 4
static const unsigned SPACE_INT= 0x20202020U;
#elif SIZEOF_INT == 8
static const unsigned SPACE_INT= 0x2020202020202020ULL;
#else
#error define the appropriate constant for a word full of spaces
#endif

// A copy of the original version of skip_trailing_space
const uchar *skip_trailing_orig(const uchar *ptr,size_t len)
{
  const uchar *end= ptr + len;

  if (len > 20)
  {
    const uchar *end_words= (const uchar *)(intptr)
      (((ulonglong)(intptr)end) / SIZEOF_INT * SIZEOF_INT);
    const uchar *start_words= (const uchar *)(intptr)
       ((((ulonglong)(intptr)ptr) + SIZEOF_INT - 1) / SIZEOF_INT * SIZEOF_INT);

    DBUG_ASSERT(((ulonglong)(intptr)ptr) >= SIZEOF_INT);
    if (end_words > ptr)
    {
      while (end > end_words && end[-1] == 0x20)
        end--;
      if (end[-1] == 0x20 && start_words < end_words)
        while (end > start_words && ((unsigned *)end)[-1] == SPACE_INT)
          end -= SIZEOF_INT;
    }
  }
  while (end > ptr && end[-1] == 0x20)
    end--;
  return (end);
}


// Read 8 bytes at a time, ignoring alignment.
// We use uint8korr which is fast on all platforms, except sparc.
const uchar *skip_trailing_unalgn(const uchar *ptr, size_t len)
{
  const uchar *end= ptr + len;
  while (end - ptr >= 8)
  {
    if (uint8korr(end-8) != 0x2020202020202020ULL)
      break;
    end-= 8;
  }
  while (end > ptr && end[-1] == 0x20)
    end--;
  return (end);
}


// Same as the original, except we skip a test which is always true.
const uchar *skip_trailing_4byte(const uchar *ptr, size_t len)
{
  const uchar *end= ptr + len;

  if (len > 20)
  {
    const uchar *end_words= (const uchar *)(intptr)
      (((ulonglong)(intptr)end) / SIZEOF_INT * SIZEOF_INT);
    const uchar *start_words= (const uchar *)(intptr)
      ((((ulonglong)(intptr)ptr) + SIZEOF_INT - 1) / SIZEOF_INT * SIZEOF_INT);

    DBUG_ASSERT(end_words > ptr);
    {
      while (end > end_words && end[-1] == 0x20)
        end--;
      if (end[-1] == 0x20 && start_words < end_words)
        while (end > start_words && ((unsigned *)end)[-1] == SPACE_INT)
          end -= SIZEOF_INT;
    }
  }
  while (end > ptr && end[-1] == 0x20)
    end--;
  return (end);
}


// Same as skip_trailing_4byte, except we read 8 bytes at a time (aligned).
const uchar *skip_trailing_8byte(const uchar *ptr, size_t len)
{
  const uchar *end= ptr + len;

  if (len > 20)
  {
    const uchar *end_words= (const uchar *)(longlong)
      (((ulonglong)(longlong)end) / 8 * 8);
    const uchar *start_words= (const uchar *)(longlong)
       ((((ulonglong)(longlong)ptr) + 8 - 1) / 8 * 8);

    DBUG_ASSERT(end_words > ptr);
    {
      while (end > end_words && end[-1] == 0x20)
        end--;
      if (end[-1] == 0x20 && start_words < end_words)
        while (end > start_words &&
               ((ulonglong *)end)[-1] == 0x2020202020202020ULL)
          end -= 8;
    }
  }
  while (end > ptr && end[-1] == 0x20)
    end--;
  return (end);
}

}