source: rtems/c/src/libnetworking/netinet/in_cksum_powerpc.c @ d3c1060

/*
 * Checksum routine for Internet Protocol family headers.
 *
 * This routine is very heavily used in the network
 * code and should be modified for each CPU to be as fast as possible.
 *
 * This implementation is the PowerPC version.
 *
 *  $Id$
 */

#include <stdio.h>                /* for puts */

#undef  ADDCARRY
#define ADDCARRY(x)     if ((x) > 0xffff) (x) -= 0xffff
#define REDUCE          {sum = (sum & 0xffff) + (sum >> 16); ADDCARRY(sum);}

/*
 * Thanks to gcc we don't have to guess
 * which registers contain sum & w.
 */

#define LDTMP(n) tmp = *((u_int *)((u_char *)w + n))

#define ADD(n)  \
  LDTMP(n);  \
  __asm__ volatile("addc %0,%0,%2" : "=r" (sum) : "0" (sum), "r" (tmp))

#define ADDC(n) \
  LDTMP(n);  \
  __asm__ volatile("adde  %0,%0,%2" : "=r" (sum) : "0" (sum), "r" (tmp))

#define MOP \
  tmp = 0; \
  __asm__ volatile("adde  %0,%0,%2" : "=r" (sum) : "0" (sum), "r" (tmp))

#define LOAD(n) junk = (u_char) *((volatile u_char *) w + n)


int
in_cksum(m, len)
        register struct mbuf *m;
        register int len;
{
        u_char junk;
        register u_short *w;
        register unsigned sum = 0;
        register unsigned tmp;
        register int mlen = 0;
        int byte_swapped = 0;
        union { char    c[2]; u_short   s; } su;

        for (;m && len; m = m->m_next) {
                if (m->m_len == 0)
                        continue;
                w = mtod(m, u_short *);
                if (mlen == -1) {
                        /*
                         * The first byte of this mbuf is the continuation
                         * of a word spanning between this mbuf and the
                         * last mbuf.
                         */

                        /* su.c[0] is already saved when scanning previous
                         * mbuf.  sum was REDUCEd when we found mlen == -1
                         */
                        su.c[1] = *(u_char *)w;
                        sum += su.s;
                        w = (u_short *)((char *)w + 1);
                        mlen = m->m_len - 1;
                        len--;
                } else
                        mlen = m->m_len;
                if (len < mlen)
                        mlen = len;
                len -= mlen;
                /*
                 * Force to long boundary so we do longword aligned
                 * memory operations
                 */
                if (3 & (int) w) {
                        REDUCE;
                        if ((1 & (int) w) && (mlen > 0)) {
                                sum <<= 8;
                                su.c[0] = *(char *)w;
                                w = (u_short *)((char *)w + 1);
                                mlen--;
                                byte_swapped = 1;
                        }
                        if ((2 & (int) w) && (mlen >= 2)) {
                                sum += *w++;
                                mlen -= 2;
                        }
                }

                /*
                 * Do as much of the checksum as possible 32 bits at at time.
                 * In fact, this loop is unrolled to keep overhead from
                 * branches small.
                 */
                while (mlen >= 32) {
                        /*
                         * Add with carry 16 words and fold in the last
                         * carry by adding a 0 with carry.
                         *
                         * The early ADD(16) and the LOAD(32) are intended
                         * to help  get the data into the cache.
                         */
                        ADD(16);
                        ADDC(0);
                        ADDC(4);
                        ADDC(8);
                        ADDC(12);
                        LOAD(32);
                        ADDC(20);
                        ADDC(24);
                        ADDC(28);
                        MOP;
                        w += 16;
                        mlen -= 32;
                }
                if (mlen >= 16) {
                        ADD(0);
                        ADDC(4);
                        ADDC(8);
                        ADDC(12);
                        MOP;
                        w += 8;
                        mlen -= 16;
                }
                if (mlen >= 8) {
                        ADD(0);
                        ADDC(4);
                        MOP;
                        w += 4;
                        mlen -= 8;
                }
                if (mlen == 0 && byte_swapped == 0)
                        continue;       /* worth 1% maybe ?? */
                REDUCE;
                while ((mlen -= 2) >= 0) {
                        sum += *w++;
                }
                if (byte_swapped) {
                        sum <<= 8;
                        byte_swapped = 0;
                        if (mlen == -1) {
                                su.c[1] = *(char *)w;
                                sum += su.s;
                                mlen = 0;
                        } else
                                mlen = -1;
                } else if (mlen == -1)
                        /*
                         * This mbuf has odd number of bytes.
                         * There could be a word split betwen
                         * this mbuf and the next mbuf.
                         * Save the last byte (to prepend to next mbuf).
                         */
                        su.c[0] = *(char *)w;
        }

        if (len)
                puts("cksum: out of data");
        if (mlen == -1) {
                /* The last mbuf has odd # of bytes. Follow the
                   standard (the odd byte is shifted left by 8 bits) */
                su.c[1] = 0;
                sum += su.s;
        }
        REDUCE;
        return (~sum & 0xffff);
}