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csum-partial_64.c

/*
 * arch/x86_64/lib/csum-partial.c
 *
 * This file contains network checksum routines that are better done
 * in an architecture-specific manner due to speed.
 */
 
#include <linux/compiler.h>
#include <linux/module.h>
#include <asm/checksum.h>

static inline unsigned short from32to16(unsigned a) 
{
      unsigned short b = a >> 16; 
      asm("addw %w2,%w0\n\t"
          "adcw $0,%w0\n" 
          : "=r" (b)
          : "0" (b), "r" (a));
      return b;
}

/*
 * Do a 64-bit checksum on an arbitrary memory area.
 * Returns a 32bit checksum.
 *
 * This isn't as time critical as it used to be because many NICs
 * do hardware checksumming these days.
 * 
 * Things tried and found to not make it faster:
 * Manual Prefetching
 * Unrolling to an 128 bytes inner loop.
 * Using interleaving with more registers to break the carry chains.
 */
static unsigned do_csum(const unsigned char *buff, unsigned len)
{
      unsigned odd, count;
      unsigned long result = 0;

      if (unlikely(len == 0))
            return result; 
      odd = 1 & (unsigned long) buff;
      if (unlikely(odd)) {
            result = *buff << 8;
            len--;
            buff++;
      }
      count = len >> 1;       /* nr of 16-bit words.. */
      if (count) {
            if (2 & (unsigned long) buff) {
                  result += *(unsigned short *)buff;
                  count--;
                  len -= 2;
                  buff += 2;
            }
            count >>= 1;            /* nr of 32-bit words.. */
            if (count) {
                  unsigned long zero;
                  unsigned count64;
                  if (4 & (unsigned long) buff) {
                        result += *(unsigned int *) buff;
                        count--;
                        len -= 4;
                        buff += 4;
                  }
                  count >>= 1;      /* nr of 64-bit words.. */

                  /* main loop using 64byte blocks */
                  zero = 0;
                  count64 = count >> 3;
                  while (count64) { 
                        asm("addq 0*8(%[src]),%[res]\n\t"
                            "adcq 1*8(%[src]),%[res]\n\t"
                            "adcq 2*8(%[src]),%[res]\n\t"
                            "adcq 3*8(%[src]),%[res]\n\t"
                            "adcq 4*8(%[src]),%[res]\n\t"
                            "adcq 5*8(%[src]),%[res]\n\t"
                            "adcq 6*8(%[src]),%[res]\n\t"
                            "adcq 7*8(%[src]),%[res]\n\t"
                            "adcq %[zero],%[res]"
                            : [res] "=r" (result)
                            : [src] "r" (buff), [zero] "r" (zero),
                            "[res]" (result));
                        buff += 64;
                        count64--;
                  }

                  /* last upto 7 8byte blocks */
                  count %= 8; 
                  while (count) { 
                        asm("addq %1,%0\n\t"
                            "adcq %2,%0\n" 
                                  : "=r" (result)
                            : "m" (*(unsigned long *)buff), 
                            "r" (zero),  "0" (result));
                        --count; 
                              buff += 8;
                  }
                  result = add32_with_carry(result>>32,
                                      result&0xffffffff); 

                  if (len & 4) {
                        result += *(unsigned int *) buff;
                        buff += 4;
                  }
            }
            if (len & 2) {
                  result += *(unsigned short *) buff;
                  buff += 2;
            }
      }
      if (len & 1)
            result += *buff;
      result = add32_with_carry(result>>32, result & 0xffffffff); 
      if (unlikely(odd)) { 
            result = from32to16(result);
            result = ((result >> 8) & 0xff) | ((result & 0xff) << 8);
      }
      return result;
}

/*
 * computes the checksum of a memory block at buff, length len,
 * and adds in "sum" (32-bit)
 *
 * returns a 32-bit number suitable for feeding into itself
 * or csum_tcpudp_magic
 *
 * this function must be called with even lengths, except
 * for the last fragment, which may be odd
 *
 * it's best to have buff aligned on a 64-bit boundary
 */
__wsum csum_partial(const void *buff, int len, __wsum sum)
{
      return (__force __wsum)add32_with_carry(do_csum(buff, len),
                                    (__force u32)sum);
}

EXPORT_SYMBOL(csum_partial);

/*
 * this routine is used for miscellaneous IP-like checksums, mainly
 * in icmp.c
 */
__sum16 ip_compute_csum(const void *buff, int len)
{
      return csum_fold(csum_partial(buff,len,0));
}
EXPORT_SYMBOL(ip_compute_csum);


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