arch/m68k/lib/checksum.c

Source file repositories/reference/linux-study-clean/arch/m68k/lib/checksum.c

File Facts

System
Linux kernel
Corpus path
arch/m68k/lib/checksum.c
Extension
.c
Size
9431 bytes
Lines
370
Domain
Architecture Layer
Bucket
arch/m68k
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

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * INET		An implementation of the TCP/IP protocol suite for the LINUX
 *		operating system.  INET is implemented using the  BSD Socket
 *		interface as the means of communication with the user level.
 *
 *		IP/TCP/UDP checksumming routines
 *
 * Authors:	Jorge Cwik, <jorge@laser.satlink.net>
 *		Arnt Gulbrandsen, <agulbra@nvg.unit.no>
 *		Tom May, <ftom@netcom.com>
 *		Andreas Schwab, <schwab@issan.informatik.uni-dortmund.de>
 *		Lots of code moved from tcp.c and ip.c; see those files
 *		for more names.
 *
 * 03/02/96	Jes Sorensen, Andreas Schwab, Roman Hodek:
 *		Fixed some nasty bugs, causing some horrible crashes.
 *		A: At some points, the sum (%0) was used as
 *		length-counter instead of the length counter
 *		(%1). Thanks to Roman Hodek for pointing this out.
 *		B: GCC seems to mess up if one uses too many
 *		data-registers to hold input values and one tries to
 *		specify d0 and d1 as scratch registers. Letting gcc
 *		choose these registers itself solves the problem.
 *
 * 1998/8/31	Andreas Schwab:
 *		Zero out rest of buffer on exception in
 *		csum_partial_copy_from_user.
 */

#include <linux/module.h>
#include <net/checksum.h>

/*
 * computes a partial checksum, e.g. for TCP/UDP fragments
 */

__wsum csum_partial(const void *buff, int len, __wsum sum)
{
	unsigned long tmp1, tmp2;
	  /*
	   * Experiments with ethernet and slip connections show that buff
	   * is aligned on either a 2-byte or 4-byte boundary.
	   */
	__asm__("movel %2,%3\n\t"
		"btst #1,%3\n\t"	/* Check alignment */
		"jeq 2f\n\t"
		"subql #2,%1\n\t"	/* buff%4==2: treat first word */
		"jgt 1f\n\t"
		"addql #2,%1\n\t"	/* len was == 2, treat only rest */
		"jra 4f\n"
	     "1:\t"
		"addw %2@+,%0\n\t"	/* add first word to sum */
		"clrl %3\n\t"
		"addxl %3,%0\n"		/* add X bit */
	     "2:\t"
		/* unrolled loop for the main part: do 8 longs at once */
		"movel %1,%3\n\t"	/* save len in tmp1 */
		"lsrl #5,%1\n\t"	/* len/32 */
		"jeq 2f\n\t"		/* not enough... */
		"subql #1,%1\n"
	     "1:\t"
		"movel %2@+,%4\n\t"
		"addxl %4,%0\n\t"
		"movel %2@+,%4\n\t"
		"addxl %4,%0\n\t"
		"movel %2@+,%4\n\t"
		"addxl %4,%0\n\t"
		"movel %2@+,%4\n\t"
		"addxl %4,%0\n\t"
		"movel %2@+,%4\n\t"
		"addxl %4,%0\n\t"
		"movel %2@+,%4\n\t"
		"addxl %4,%0\n\t"
		"movel %2@+,%4\n\t"
		"addxl %4,%0\n\t"
		"movel %2@+,%4\n\t"
		"addxl %4,%0\n\t"
		"dbra %1,1b\n\t"
		"clrl %4\n\t"
		"addxl %4,%0\n\t"	/* add X bit */
		"clrw %1\n\t"
		"subql #1,%1\n\t"
		"jcc 1b\n"
	     "2:\t"
		"movel %3,%1\n\t"	/* restore len from tmp1 */
		"andw #0x1c,%3\n\t"	/* number of rest longs */
		"jeq 4f\n\t"
		"lsrw #2,%3\n\t"
		"subqw #1,%3\n"

Annotation

Implementation Notes