linux-stable-rt/include/asm-cris/arch-v10/checksum.h

#ifndef _CRIS_ARCH_CHECKSUM_H
#define _CRIS_ARCH_CHECKSUM_H

/* Checksum some values used in TCP/UDP headers.
 *
 * The gain by doing this in asm is that C will not generate carry-additions
 * for the 32-bit components of the checksum, so otherwise we would have had
 * to split all of those into 16-bit components, then add.
 */

static inline unsigned int
csum_tcpudp_nofold(unsigned long saddr, unsigned long daddr, unsigned short len,
		   unsigned short proto, unsigned int sum)
{
	int res;
	__asm__ ("add.d %2, %0\n\t"
		 "ax\n\t"
		 "add.d %3, %0\n\t"
		 "ax\n\t"
		 "add.d %4, %0\n\t"
		 "ax\n\t"
		 "addq 0, %0\n"
	: "=r" (res)
	: "0" (sum), "r" (daddr), "r" (saddr), "r" ((ntohs(len) << 16) + (proto << 8)));

	return res;
}	

#endif