Prepare for radical source tree reorganization.zack/build-layout-experiment

All top-level files and directories are moved into a temporary storage
directory, REORG.TODO, except for files that will certainly still
exist in their current form at top level when we're done (COPYING,
COPYING.LIB, LICENSES, NEWS, README), all old ChangeLog files (which
are moved to the new directory OldChangeLogs, instead), and the
generated file INSTALL (which is just deleted; in the new order, there
will be no generated files checked into version control).

1 files changed, 182 insertions, 0 deletions

diff --git a/REORG.TODO/sysdeps/i386/i586/strlen.S b/REORG.TODO/sysdeps/i386/i586/strlen.S
new file mode 100644
index 0000000000..cfea2e020f
--- /dev/null
+++ b/REORG.TODO/sysdeps/i386/i586/strlen.S
@@ -0,0 +1,182 @@
+/* strlen -- Compute length of NUL terminated string.
+   Highly optimized version for ix86, x>=5.
+   Copyright (C) 1995-2017 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+   Contributed by Ulrich Drepper, <drepper@gnu.ai.mit.edu>.
+
+   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
+   <http://www.gnu.org/licenses/>.  */
+
+#include <sysdep.h>
+#include "asm-syntax.h"
+
+/* This version is especially optimized for the i586 (and following?)
+   processors.  This is mainly done by using the two pipelines.  The
+   version optimized for i486 is weak in this aspect because to get
+   as much parallelism we have to execute some *more* instructions.
+
+   The code below is structured to reflect the pairing of the instructions
+   as *I think* it is.  I have no processor data book to verify this.
+   If you find something you think is incorrect let me know.  */
+
+
+/* The magic value which is used throughout in the whole code.  */
+#define magic 0xfefefeff
+
+#define PARMS	4		/* no space for saved regs */
+#define STR	PARMS
+
+	.text
+ENTRY (strlen)
+
+	movl STR(%esp), %eax
+	movl $3, %edx		/* load mask (= 3) */
+
+	andl %eax, %edx		/* separate last two bits of address */
+
+	jz L(1)			/* aligned => start loop */
+	jp L(0)			/* exactly two bits set */
+
+	cmpb %dh, (%eax)	/* is byte NUL? */
+	je L(2)			/* yes => return */
+
+	incl %eax		/* increment pointer */
+	cmpb %dh, (%eax)	/* is byte NUL? */
+
+	je L(2)			/* yes => return */
+
+	incl %eax		/* increment pointer */
+	xorl $2, %edx
+
+	jz L(1)
+
+L(0):	cmpb %dh, (%eax)	/* is byte NUL? */
+	je L(2)			/* yes => return */
+
+	incl %eax		/* increment pointer */
+	xorl %edx, %edx		/* We need %edx == 0 for later */
+
+      /* We exit the loop if adding MAGIC_BITS to LONGWORD fails to
+	 change any of the hole bits of LONGWORD.
+
+	 1) Is this safe?  Will it catch all the zero bytes?
+	 Suppose there is a byte with all zeros.  Any carry bits
+	 propagating from its left will fall into the hole at its
+	 least significant bit and stop.  Since there will be no
+	 carry from its most significant bit, the LSB of the
+	 byte to the left will be unchanged, and the zero will be
+	 detected.
+
+	 2) Is this worthwhile?  Will it ignore everything except
+	 zero bytes?  Suppose every byte of LONGWORD has a bit set
+	 somewhere.  There will be a carry into bit 8.	If bit 8
+	 is set, this will carry into bit 16.  If bit 8 is clear,
+	 one of bits 9-15 must be set, so there will be a carry
+	 into bit 16.  Similarly, there will be a carry into bit
+	 24.  If one of bits 24-31 is set, there will be a carry
+	 into bit 32 (=carry flag), so all of the hole bits will
+	 be changed.
+
+	 Note: %edx == 0 in any case here.  */
+
+L(1):
+	movl (%eax), %ecx	/* get word (= 4 bytes) in question */
+	addl $4, %eax		/* adjust pointer for *next* word */
+
+	subl %ecx, %edx		/* first step to negate word */
+	addl $magic, %ecx	/* add magic word */
+
+	decl %edx		/* complete negation of word */
+	jnc L(3)		/* previous addl caused overflow? */
+
+	xorl %ecx, %edx		/* (word+magic)^word */
+
+	andl $~magic, %edx	/* any of the carry flags set? */
+
+	jne L(3)		/* yes => determine byte */
+
+
+	movl (%eax), %ecx	/* get word (= 4 bytes) in question */
+	addl $4, %eax		/* adjust pointer for *next* word */
+
+	subl %ecx, %edx		/* first step to negate word */
+	addl $magic, %ecx	/* add magic word */
+
+	decl %edx		/* complete negation of word */
+	jnc L(3)		/* previous addl caused overflow? */
+
+	xorl %ecx, %edx		/* (word+magic)^word */
+
+	andl $~magic, %edx	/* any of the carry flags set? */
+
+	jne L(3)		/* yes => determine byte */
+
+
+	movl (%eax), %ecx	/* get word (= 4 bytes) in question */
+	addl $4, %eax		/* adjust pointer for *next* word */
+
+	subl %ecx, %edx		/* first step to negate word */
+	addl $magic, %ecx	/* add magic word */
+
+	decl %edx		/* complete negation of word */
+	jnc L(3)		/* previous addl caused overflow? */
+
+	xorl %ecx, %edx		/* (word+magic)^word */
+
+	andl $~magic, %edx	/* any of the carry flags set? */
+
+	jne L(3)		/* yes => determine byte */
+
+
+	movl (%eax), %ecx	/* get word (= 4 bytes) in question */
+	addl $4, %eax		/* adjust pointer for *next* word */
+
+	subl %ecx, %edx		/* first step to negate word */
+	addl $magic, %ecx	/* add magic word */
+
+	decl %edx		/* complete negation of word */
+	jnc L(3)		/* previous addl caused overflow? */
+
+	xorl %ecx, %edx		/* (word+magic)^word */
+
+	andl $~magic, %edx	/* any of the carry flags set? */
+
+	je L(1)			/* no => start loop again */
+
+
+L(3):	subl $4, %eax		/* correct too early pointer increment */
+	subl $magic, %ecx
+
+	cmpb $0, %cl		/* lowest byte NUL? */
+	jz L(2)			/* yes => return */
+
+	inc %eax		/* increment pointer */
+	testb %ch, %ch		/* second byte NUL? */
+
+	jz L(2)			/* yes => return */
+
+	shrl $16, %ecx		/* make upper bytes accessible */
+	incl %eax		/* increment pointer */
+
+	cmpb $0, %cl		/* is third byte NUL? */
+	jz L(2)			/* yes => return */
+
+	incl %eax		/* increment pointer */
+
+L(2):	subl STR(%esp), %eax	/* now compute the length as difference
+				   between start and terminating NUL
+				   character */
+	ret
+END (strlen)
+libc_hidden_builtin_def (strlen)