LXR linux/arch/x86/lib/csum-partial

   1/*
   2 * arch/x86_64/lib/csum-partial.c
   3 *
   4 * This file contains network checksum routines that are better done
   5 * in an architecture-specific manner due to speed.
   6 */
   7 
   8#include <linux/compiler.h>
   9#include <linux/module.h>
  10#include <asm/checksum.h>
  11
  12static inline unsigned short from32to16(unsigned a) 
  13{
  14        unsigned short b = a >> 16; 
  15        asm("addw %w2,%w0\n\t"
  16            "adcw $0,%w0\n" 
  17            : "=r" (b)
  18            : "0" (b), "r" (a));
  19        return b;
  20}
  21
  22/*
  23 * Do a 64-bit checksum on an arbitrary memory area.
  24 * Returns a 32bit checksum.
  25 *
  26 * This isn't as time critical as it used to be because many NICs
  27 * do hardware checksumming these days.
  28 * 
  29 * Things tried and found to not make it faster:
  30 * Manual Prefetching
  31 * Unrolling to an 128 bytes inner loop.
  32 * Using interleaving with more registers to break the carry chains.
  33 */
  34static unsigned do_csum(const unsigned char *buff, unsigned len)
  35{
  36        unsigned odd, count;
  37        unsigned long result = 0;
  38
  39        if (unlikely(len == 0))
  40                return result; 
  41        odd = 1 & (unsigned long) buff;
  42        if (unlikely(odd)) {
  43                result = *buff << 8;
  44                len--;
  45                buff++;
  46        }
  47        count = len >> 1;               /* nr of 16-bit words.. */
  48        if (count) {
  49                if (2 & (unsigned long) buff) {
  50                        result += *(unsigned short *)buff;
  51                        count--;
  52                        len -= 2;
  53                        buff += 2;
  54                }
  55                count >>= 1;            /* nr of 32-bit words.. */
  56                if (count) {
  57                        unsigned long zero;
  58                        unsigned count64;
  59                        if (4 & (unsigned long) buff) {
  60                                result += *(unsigned int *) buff;
  61                                count--;
  62                                len -= 4;
  63                                buff += 4;
  64                        }
  65                        count >>= 1;    /* nr of 64-bit words.. */
  66
  67                        /* main loop using 64byte blocks */
  68                        zero = 0;
  69                        count64 = count >> 3;
  70                        while (count64) { 
  71                                asm("addq 0*8(%[src]),%[res]\n\t"
  72                                    "adcq 1*8(%[src]),%[res]\n\t"
  73                                    "adcq 2*8(%[src]),%[res]\n\t"
  74                                    "adcq 3*8(%[src]),%[res]\n\t"
  75                                    "adcq 4*8(%[src]),%[res]\n\t"
  76                                    "adcq 5*8(%[src]),%[res]\n\t"
  77                                    "adcq 6*8(%[src]),%[res]\n\t"
  78                                    "adcq 7*8(%[src]),%[res]\n\t"
  79                                    "adcq %[zero],%[res]"
  80                                    : [res] "=r" (result)
  81                                    : [src] "r" (buff), [zero] "r" (zero),
  82                                    "[res]" (result));
  83                                buff += 64;
  84                                count64--;
  85                        }
  86
  87                        /* last up to 7 8byte blocks */
  88                        count %= 8; 
  89                        while (count) { 
  90                                asm("addq %1,%0\n\t"
  91                                    "adcq %2,%0\n" 
  92                                            : "=r" (result)
  93                                    : "m" (*(unsigned long *)buff), 
  94                                    "r" (zero),  "0" (result));
  95                                --count; 
  96                                        buff += 8;
  97                        }
  98                        result = add32_with_carry(result>>32,
  99                                                  result&0xffffffff); 
 100
 101                        if (len & 4) {
 102                                result += *(unsigned int *) buff;
 103                                buff += 4;
 104                        }
 105                }
 106                if (len & 2) {
 107                        result += *(unsigned short *) buff;
 108                        buff += 2;
 109                }
 110        }
 111        if (len & 1)
 112                result += *buff;
 113        result = add32_with_carry(result>>32, result & 0xffffffff); 
 114        if (unlikely(odd)) { 
 115                result = from32to16(result);
 116                result = ((result >> 8) & 0xff) | ((result & 0xff) << 8);
 117        }
 118        return result;
 119}
 120
 121/*
 122 * computes the checksum of a memory block at buff, length len,
 123 * and adds in "sum" (32-bit)
 124 *
 125 * returns a 32-bit number suitable for feeding into itself
 126 * or csum_tcpudp_magic
 127 *
 128 * this function must be called with even lengths, except
 129 * for the last fragment, which may be odd
 130 *
 131 * it's best to have buff aligned on a 64-bit boundary
 132 */
 133__wsum csum_partial(const void *buff, int len, __wsum sum)
 134{
 135        return (__force __wsum)add32_with_carry(do_csum(buff, len),
 136                                                (__force u32)sum);
 137}
 138
 139/*
 140 * this routine is used for miscellaneous IP-like checksums, mainly
 141 * in icmp.c
 142 */
 143__sum16 ip_compute_csum(const void *buff, int len)
 144{
 145        return csum_fold(csum_partial(buff,len,0));
 146}
 147EXPORT_SYMBOL(ip_compute_csum);
 148
 149