checksum.c

来自「内核linux2.4.20,可跟rtlinux3.2打补丁 组成实时linux系」· C语言 代码 · 共 41 行

/*
 *  arch/s390/lib/checksum.c
 *    S390 fast network checksum routines
 *
 *  S390 version
 *    Copyright (C) 1999 IBM Deutschland Entwicklung GmbH, IBM Corporation
 *    Author(s): Ulrich Hild        (first version),
 *               Martin Schwidefsky ([e-mail]),
 *               Denis Joseph Barrow ([e-mail],[e-mail]),
 *
 * This file contains network checksum routines
 */
 
#include <linux/string.h>
#include <linux/types.h>
#include <asm/uaccess.h>
#include <asm/byteorder.h>
#include <asm/checksum.h>

/*
 * computes a partial checksum, e.g. for TCP/UDP fragments
 */
unsigned int
csum_partial (const unsigned char *buff, int len, unsigned int sum)
{
	  /*
	   * Experiments with ethernet and slip connections show that buff
	   * is aligned on either a 2-byte or 4-byte boundary.
	   */
        __asm__ __volatile__ (
                "    lgr  2,%1\n"    /* address in gpr 2 */
                "    lgfr 3,%2\n"    /* length in gpr 3 */
                "0:  cksm %0,2\n"    /* do checksum on longs */
                "    jo   0b\n"
                : "+&d" (sum)
                : "d" (buff), "d" (len)
                : "cc", "2", "3" );
        return sum;
}