arch/alpha/lib/memchr.S

Source file repositories/reference/linux-study-clean/arch/alpha/lib/memchr.S

File Facts

System
Linux kernel
Corpus path
arch/alpha/lib/memchr.S
Extension
.S
Size
5049 bytes
Lines
166
Domain
Architecture Layer
Bucket
arch/alpha
Inferred role
Architecture Layer: exported/initcall integration point
Status
integration implementation candidate

Why This File Exists

CPU and platform-specific kernel glue: boot entry, traps, syscall entry, interrupts, page tables, context switch, and low-level barriers.

Dependency Surface

Detected Declarations

Annotated Snippet

This file is part of the GNU C Library.
   Contributed by David Mosberger (davidm@cs.arizona.edu).

   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., 59 Temple Place - Suite 330,
   Boston, MA 02111-1307, USA.  */

/* Finds characters in a memory area.  Optimized for the Alpha:

      - memory accessed as aligned quadwords only
      - uses cmpbge to compare 8 bytes in parallel
      - does binary search to find 0 byte in last
        quadword (HAKMEM needed 12 instructions to
        do this instead of the 9 instructions that
        binary search needs).

For correctness consider that:

      - only minimum number of quadwords may be accessed
      - the third argument is an unsigned long
*/
#include <linux/export.h>
        .set noreorder
        .set noat

	.globl memchr
	.ent memchr
memchr:
	.frame $30,0,$26,0
	.prologue 0

	# Hack -- if someone passes in (size_t)-1, hoping to just
	# search til the end of the address space, we will overflow
	# below when we find the address of the last byte.  Given
	# that we will never have a 56-bit address space, cropping
	# the length is the easiest way to avoid trouble.
	zap	$18, 0x80, $5	#-e0	:

	beq	$18, $not_found	# .. e1 :
        ldq_u   $1, 0($16)	# e1	: load first quadword
	insbl	$17, 1, $2	# .. e0 : $2 = 000000000000ch00
	and	$17, 0xff, $17	#-e0    : $17 = 00000000000000ch
	cmpult	$18, 9, $4	# .. e1 :
	or	$2, $17, $17	# e0    : $17 = 000000000000chch
        lda     $3, -1($31)	# .. e1 :
	sll	$17, 16, $2	#-e0    : $2 = 00000000chch0000
	addq	$16, $5, $5	# .. e1 :
	or	$2, $17, $17	# e1    : $17 = 00000000chchchch
	unop			#	:
	sll	$17, 32, $2	#-e0    : $2 = chchchch00000000
	or	$2, $17, $17	# e1	: $17 = chchchchchchchch
	extql	$1, $16, $7	# e0    : 
	beq	$4, $first_quad	# .. e1 :

	ldq_u	$6, -1($5)	#-e1	: eight or less bytes to search
	extqh	$6, $16, $6	# .. e0 :
	mov	$16, $0		# e0	:
	or	$7, $6, $1	# .. e1 : $1 = quadword starting at $16

Annotation

Implementation Notes