From 67a87b936eaab25dc983e979e5a548256d1a527a Mon Sep 17 00:00:00 2001
From: Roland McGrath <roland@gnu.org>
Date: Tue, 21 Feb 1995 08:07:34 +0000
Subject: * string/Makefile (distribute): Add pagecopy.h.

	* sysdeps/mach/pagecopy.h: New file.
	* sysdeps/generic/pagecopy.h: New file.
	* sysdeps/generic/memcpy.c: Include pagecopy.h; call
 	PAGE_COPY_FWD_MAYBE first when word aligned.
	* sysdeps/generic/memmove.c: Likewise.
---
 sysdeps/generic/pagecopy.h | 74 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 74 insertions(+)
 create mode 100644 sysdeps/generic/pagecopy.h

(limited to 'sysdeps/generic/pagecopy.h')

diff --git a/sysdeps/generic/pagecopy.h b/sysdeps/generic/pagecopy.h
new file mode 100644
index 0000000..07202a3
--- /dev/null
+++ b/sysdeps/generic/pagecopy.h
@@ -0,0 +1,74 @@
+/* Macros for copying by pages; used in memcpy, memmove.  Generic macros.
+Copyright (C) 1995 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 Library General Public License as
+published by the Free Software Foundation; either version 2 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
+Library General Public License for more details.
+
+You should have received a copy of the GNU Library General Public
+License along with the GNU C Library; see the file COPYING.LIB.  If
+not, write to the Free Software Foundation, Inc., 675 Mass Ave,
+Cambridge, MA 02139, USA.  */
+
+/* This file defines the macro:
+
+   PAGE_COPY_FWD_MAYBE (dstp, srcp, nbytes_left, nbytes)
+
+   which is invoked like WORD_COPY_FWD et al.  The pointers should be at
+   least word aligned.  This will check if virtual copying by pages can and
+   should be done and do it if so.
+
+   System-specific pagecopy.h files should define these macros and then
+   #include this file:
+
+   PAGE_COPY_THRESHOLD
+   -- Minimum size for which virtual copying by pages is worthwhile.
+
+   PAGE_SIZE
+   -- Size of a page.
+
+   PAGE_COPY_FWD (dstp, srcp, nbytes_left, nbytes)
+   -- Macro to perform the virtual copy operation.
+   The pointers will be aligned to PAGE_SIZE bytes.
+*/
+
+
+#if PAGE_COPY_THRESHOLD
+
+#define PAGE_COPY_FWD_MAYBE(dstp, srcp, nbytes_left, nbytes)		      \
+  do									      \
+    {									      \
+      if ((nbytes) >= PAGE_COPY_THRESHOLD &&				      \
+	  PAGE_OFFSET (dstp) == PAGE_OFFSET (srcp))			      \
+	{								      \
+	  /* The amount to copy is past the threshold for copying	      \
+	     pages virtually with kernel VM operations, and the		      \
+	     source and destination addresses have the same alignment.  */    \
+	  size_t nbytes_before = PAGE_OFFSET (PAGE_SIZE - PAGE_OFFSET (dstp));\
+	  if (nbytes_before != 0)					      \
+	    {								      \
+	      /* First copy the words before the first page boundary.  */     \
+	      WORD_COPY_FWD (dstp, srcp, nbytes_left, nbytes_before);	      \
+	      nbytes_before -= nbytes_left;				      \
+	      nbytes -= nbytes_before;					      \
+	    }								      \
+	  if (nbytes_before == 0)					      \
+	    PAGE_COPY_FWD (dstp, srcp, nbytes_left, nbytes);		      \
+	}								      \
+    } while (0)
+
+/* The page size is always a power of two, so we can avoid modulo division.  */
+#define PAGE_OFFSET(n)	((n) & (PAGE_SIZE - 1))
+
+#else
+
+#define PAGE_COPY_FWD_MAYBE(dstp, srcp, nbytes_left, nbytes) /* nada */
+
+#endif
-- 
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