string: Add internal memswap implementation

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.
Reviewed-by: Noah Goldstein <goldstein.w.n@gmail.com>

3 files changed, 245 insertions, 0 deletions

diff --git a/string/Makefile b/string/Makefile
index 040a38d..850bfba 100644
--- a/string/Makefile
+++ b/string/Makefile
@@ -211,6 +211,18 @@ 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 0000000..162beb9
--- /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;
+          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 0000000..f09dae1
--- /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;
+    }
+}