Re: [PATCH v8 1/7] string: Add internal memswap implementation

[Noah Goldstein <goldstein.w.n@gmail.com>]

On Tue, Oct 3, 2023 at 5:22 AM Adhemerval Zanella
<adhemerval.zanella@linaro.org> wrote:
>
> The prototype is:
>
>   void __memswap (void *restrict p1, void *restrict p2, size_t n)
>
> The function swaps the content of two memory blocks P1 and P2 of
> len N.  Memory overlap is NOT handled.
>
> It will be used on qsort optimization.
>
> Checked on x86_64-linux-gnu and aarch64-linux-gnu.
> ---
>  string/Makefile           |  12 +++
>  string/test-memswap.c     | 192 ++++++++++++++++++++++++++++++++++++++
>  sysdeps/generic/memswap.h |  41 ++++++++
>  3 files changed, 245 insertions(+)
>  create mode 100644 string/test-memswap.c
>  create mode 100644 sysdeps/generic/memswap.h
>
> diff --git a/string/Makefile b/string/Makefile
> index 8cdfd5b000..fb101db778 100644
> --- a/string/Makefile
> +++ b/string/Makefile
> @@ -209,6 +209,18 @@ tests := \
>    tst-xbzero-opt \
>  # tests
>
> +tests-static-internal := \
> +  test-memswap \
> +# tests-static-internal
> +
> +tests-internal := \
> +  $(tests-static-internal) \
> +  # tests-internal
> +
> +tests-static := \
> +  $(tests-static-internal) \
> +  # tests-static
> +
>  # Both tests require the .mo translation files generated by msgfmt.
>  tests-translation := \
>    tst-strerror \
> diff --git a/string/test-memswap.c b/string/test-memswap.c
> new file mode 100644
> index 0000000000..162beb91e3
> --- /dev/null
> +++ b/string/test-memswap.c
> @@ -0,0 +1,192 @@
> +/* Test and measure memcpy functions.
> +   Copyright (C) 2023 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library 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
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#include <string.h>
> +#include <support/check.h>
> +#include <memswap.h>
> +
> +#define TEST_MAIN
> +#define BUF1PAGES 3
> +#include "test-string.h"
> +
> +static unsigned char *ref1;
> +static unsigned char *ref2;
> +
> +static void
> +do_one_test (unsigned char *p1, unsigned char *ref1, unsigned char *p2,
> +            unsigned char *ref2, size_t len)
> +{
> +  __memswap (p1, p2, len);
> +
> +  TEST_COMPARE_BLOB (p1, len, ref2, len);
> +  TEST_COMPARE_BLOB (p2, len, ref1, len);
> +}
> +
> +static inline void
> +do_test (size_t align1, size_t align2, size_t len)
> +{
> +  align1 &= page_size;
> +  if (align1 + len >= page_size)
> +    return;
> +
> +  align2 &= page_size;
> +  if (align2 + len >= page_size)
> +    return;
> +
> +  unsigned char *p1 = buf1 + align1;
> +  unsigned char *p2 = buf2 + align2;
> +  for (size_t repeats = 0; repeats < 2; ++repeats)
> +    {
> +      size_t i, j;
> +      for (i = 0, j = 1; i < len; i++, j += 23)
> +       {
> +         ref1[i] = p1[i] = j;
> +         ref2[i] = p2[i] = UCHAR_MAX - j;
> +       }
> +
> +      do_one_test (p1, ref1, p2, ref2, len);
> +    }
> +}
> +
> +static void
> +do_random_tests (void)
> +{
> +  for (size_t n = 0; n < ITERATIONS; n++)
> +    {
> +      size_t len, size, size1, size2, align1, align2;
> +
> +      if (n == 0)
> +        {
> +          len = getpagesize ();
> +          size = len + 512;
> +          size1 = size;
> +          size2 = size;
> +          align1 = 512;
> +          align2 = 512;
> +        }
> +      else
> +        {
> +          if ((random () & 255) == 0)
> +            size = 65536;
> +          else
> +            size = 768;
> +          if (size > page_size)
> +            size = page_size;
> +          size1 = size;
> +          size2 = size;
> +          size_t i = random ();
> +          if (i & 3)
> +            size -= 256;
> +          if (i & 1)
> +            size1 -= 256;
> +          if (i & 2)
> +            size2 -= 256;
Some tests with misaligned size seem in order.
> +          if (i & 4)
> +            {
> +              len = random () % size;
> +              align1 = size1 - len - (random () & 31);
> +              align2 = size2 - len - (random () & 31);
> +              if (align1 > size1)
> +                align1 = 0;
> +              if (align2 > size2)
> +                align2 = 0;
> +            }
> +          else
> +            {
> +              align1 = random () & 63;
> +              align2 = random () & 63;
> +              len = random () % size;
> +              if (align1 + len > size1)
> +                align1 = size1 - len;
> +              if (align2 + len > size2)
> +                align2 = size2 - len;
> +            }
> +        }
> +      unsigned char *p1 = buf1 + page_size - size1;
> +      unsigned char *p2 = buf2 + page_size - size2;
> +      size_t j = align1 + len + 256;
> +      if (j > size1)
> +        j = size1;
> +      for (size_t i = 0; i < j; ++i)
> +       ref1[i] = p1[i] = random () & 255;
> +
> +      j = align2 + len + 256;
> +      if (j > size2)
> +       j = size2;
> +
> +      for (size_t i = 0; i < j; ++i)
> +       ref2[i] = p2[i] = random () & 255;
> +
> +      do_one_test (p1 + align1, ref1 + align1, p2 + align2, ref2 + align2, len);
> +    }
> +}
> +
> +static int
> +test_main (void)
> +{
> +  test_init ();
> +  /* Use the start of buf1 for reference buffers.  */
> +  ref1 = buf1;
> +  ref2 = buf1 + page_size;
> +  buf1 = ref2 + page_size;
> +
> +  printf ("%23s", "");
> +  printf ("\t__memswap\n");
> +
> +  for (size_t i = 0; i < 18; ++i)
> +    {
> +      do_test (0, 0, 1 << i);
> +      do_test (i, 0, 1 << i);
> +      do_test (0, i, 1 << i);
> +      do_test (i, i, 1 << i);
> +    }
> +
> +  for (size_t i = 0; i < 32; ++i)
> +    {
> +      do_test (0, 0, i);
> +      do_test (i, 0, i);
> +      do_test (0, i, i);
> +      do_test (i, i, i);
> +    }
> +
> +  for (size_t i = 3; i < 32; ++i)
> +    {
> +      if ((i & (i - 1)) == 0)
> +        continue;
> +      do_test (0, 0, 16 * i);
> +      do_test (i, 0, 16 * i);
> +      do_test (0, i, 16 * i);
> +      do_test (i, i, 16 * i);
> +    }
> +
> +  for (size_t i = 19; i <= 25; ++i)
> +    {
> +      do_test (255, 0, 1 << i);
> +      do_test (0, 4000, 1 << i);
> +      do_test (0, 255, i);
> +      do_test (0, 4000, i);
> +    }
> +
> +  do_test (0, 0, getpagesize ());
> +
> +  do_random_tests ();
> +
> +  return 0;
> +}
> +
> +#include <support/test-driver.c>
> diff --git a/sysdeps/generic/memswap.h b/sysdeps/generic/memswap.h
> new file mode 100644
> index 0000000000..f09dae1ebb
> --- /dev/null
> +++ b/sysdeps/generic/memswap.h
> @@ -0,0 +1,41 @@
> +/* Swap the content of two memory blocks, overlap is NOT handled.
> +   Copyright (C) 2023 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library 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
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#include <string.h>
> +
> +static inline void
> +__memswap (void *__restrict p1, void *__restrict p2, size_t n)
> +{
> +  /* Use multiple small memcpys with constant size to enable inlining on most
> +     targets.  */
> +  enum { SWAP_GENERIC_SIZE = 32 };
> +  unsigned char tmp[SWAP_GENERIC_SIZE];
> +  while (n > SWAP_GENERIC_SIZE)
> +    {
> +      memcpy (tmp, p1, SWAP_GENERIC_SIZE);
> +      p1 = __mempcpy (p1, p2, SWAP_GENERIC_SIZE);
> +      p2 = __mempcpy (p2, tmp, SWAP_GENERIC_SIZE);
> +      n -= SWAP_GENERIC_SIZE;
> +    }
> +  while (n > 0)
> +    {
> +      unsigned char t = ((unsigned char *)p1)[--n];
> +      ((unsigned char *)p1)[n] = ((unsigned char *)p2)[n];
> +      ((unsigned char *)p2)[n] = t;
> +    }
> +}
> --
> 2.34.1
>