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Annotation of 43BSD/etc/timed/vax/cksum.c, revision 1.1

1.1     ! root        1: /*
        !             2:  * Copyright (c) 1983 Regents of the University of California.
        !             3:  * All rights reserved.  The Berkeley software License Agreement
        !             4:  * specifies the terms and conditions for redistribution.
        !             5:  */
        !             6: 
        !             7: #ifndef lint
        !             8: static char sccsid[] = "@(#)cksum.c    1.2 (Berkeley) 9/18/85";
        !             9: #endif not lint
        !            10: 
        !            11: #include <sys/types.h>
        !            12: 
        !            13: #define ADD    asm("adwc (r9)+,r8;");
        !            14: 
        !            15: /* computes the checksum for ip packets for the VAX */
        !            16: 
        !            17: in_cksum(addr, len)
        !            18: u_short *addr;
        !            19: int len;
        !            20: {
        !            21:        register int nleft = len;       /* on vax, (user mode), r11 */
        !            22: #ifndef lint
        !            23:        register int xxx;               /* on vax, (user mode), r10 */
        !            24: #endif not lint
        !            25:        register u_short *w = addr;     /* on vax, known to be r9 */
        !            26:        register int sum = 0;           /* on vax, known to be r8 */
        !            27: 
        !            28:        if (((int)w&0x2) && nleft >= 2) {
        !            29:                sum += *w++;
        !            30:                nleft -= 2;
        !            31:        }
        !            32:        while ((nleft -= 32) >= 0) {
        !            33:                asm("clrl r0");         /* clears carry */
        !            34:                ADD; ADD; ADD; ADD; ADD; ADD; ADD; ADD;
        !            35:                asm("adwc $0,r8");
        !            36:        }
        !            37:        nleft += 32;
        !            38:        while ((nleft -= 8) >= 0) {
        !            39:                asm("clrl r0");
        !            40:                ADD; ADD;
        !            41:                asm("adwc $0,r8");
        !            42:        }
        !            43:        nleft += 8;
        !            44:        { asm("ashl $-16,r8,r0; addw2 r0,r8");
        !            45:          asm("adwc $0,r8; movzwl r8,r8"); }
        !            46:        while ((nleft -= 2) >= 0) {
        !            47:                asm("movzwl (r9)+,r0; addl2 r0,r8");
        !            48:        }
        !            49:        if (nleft == -1) {
        !            50:                sum += *(u_char *)w;
        !            51:        }
        !            52: 
        !            53:        { asm("ashl $-16,r8,r0; addw2 r0,r8; adwc $0,r8");
        !            54:          asm("mcoml r8,r8; movzwl r8,r8"); }
        !            55:        return (sum);
        !            56: }

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