arch/x86_64/lib/csum-partial.c

   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
  12 #define __force_inline inline __attribute__((always_inline))
  13
  14 static inline unsigned short from32to16(unsigned a)
  15 {
  16         unsigned short b = a >> 16;
  17         asm("addw %w2,%w0\n\t"
  18             "adcw $0,%w0\n"
  19             : "=r" (b)
  20             : "0" (b), "r" (a));
  21         return b;
  22 }
  23
  24 /*
  25  * Do a 64-bit checksum on an arbitrary memory area.
  26  * Returns a 32bit checksum.
  27  *
  28  * This isn't as time critical as it used to be because many NICs
  29  * do hardware checksumming these days.
  30  *
  31  * Things tried and found to not make it faster:
  32  * Manual Prefetching
  33  * Unrolling to an 128 bytes inner loop.
  34  * Using interleaving with more registers to break the carry chains.
  35  */
  36 static __force_inline unsigned do_csum(const unsigned char *buff, unsigned len)
  37 {
  38         unsigned odd, count;
  39         unsigned long result = 0;
  40
  41         if (unlikely(len == 0))
  42                 return result;
  43         odd = 1 & (unsigned long) buff;
  44         if (unlikely(odd)) {
  45                 result = *buff << 8;
  46                 len--;
  47                 buff++;
  48         }
  49         count = len >> 1;               /* nr of 16-bit words.. */
  50         if (count) {
  51                 if (2 & (unsigned long) buff) {
  52                         result += *(unsigned short *)buff;
  53                         count--;
  54                         len -= 2;
  55                         buff += 2;
  56                 }
  57                 count >>= 1;            /* nr of 32-bit words.. */
  58                 if (count) {
  59                         unsigned long zero;
  60                         unsigned count64;
  61                         if (4 & (unsigned long) buff) {
  62                                 result += *(unsigned int *) buff;
  63                                 count--;
  64                                 len -= 4;
  65                                 buff += 4;
  66                         }
  67                         count >>= 1;    /* nr of 64-bit words.. */
  68
  69                         /* main loop using 64byte blocks */
  70                         zero = 0;
  71                         count64 = count >> 3;
  72                         while (count64) {
  73                                 asm("addq 0*8(%[src]),%[res]\n\t"
  74                                     "adcq 1*8(%[src]),%[res]\n\t"
  75                                     "adcq 2*8(%[src]),%[res]\n\t"
  76                                     "adcq 3*8(%[src]),%[res]\n\t"
  77                                     "adcq 4*8(%[src]),%[res]\n\t"
  78                                     "adcq 5*8(%[src]),%[res]\n\t"
  79                                     "adcq 6*8(%[src]),%[res]\n\t"
  80                                     "adcq 7*8(%[src]),%[res]\n\t"
  81                                     "adcq %[zero],%[res]"
  82                                     : [res] "=r" (result)
  83                                     : [src] "r" (buff), [zero] "r" (zero),
  84                                     "[res]" (result));
  85                                 buff += 64;
  86                                 count64--;
  87                         }
  88
  89                         /* last upto 7 8byte blocks */
  90                         count %= 8;
  91                         while (count) {
  92                                 asm("addq %1,%0\n\t"
  93                                     "adcq %2,%0\n"
  94                                             : "=r" (result)
  95                                     : "m" (*(unsigned long *)buff),
  96                                     "r" (zero),  "0" (result));
  97                                 --count;
  98                                         buff += 8;
  99                         }
 100                         result = add32_with_carry(result>>32,
 101                                                   result&0xffffffff);
 102
 103                         if (len & 4) {
 104                                 result += *(unsigned int *) buff;
 105                                 buff += 4;
 106                         }
 107                 }
 108                 if (len & 2) {
 109                         result += *(unsigned short *) buff;
 110                         buff += 2;
 111                 }
 112         }
 113         if (len & 1)
 114                 result += *buff;
 115         result = add32_with_carry(result>>32, result & 0xffffffff);
 116         if (unlikely(odd)) {
 117                 result = from32to16(result);
 118                 result = ((result >> 8) & 0xff) | ((result & 0xff) << 8);
 119         }
 120         return result;
 121 }
 122
 123 /*
 124  * computes the checksum of a memory block at buff, length len,
 125  * and adds in "sum" (32-bit)
 126  *
 127  * returns a 32-bit number suitable for feeding into itself
 128  * or csum_tcpudp_magic
 129  *
 130  * this function must be called with even lengths, except
 131  * for the last fragment, which may be odd
 132  *
 133  * it's best to have buff aligned on a 64-bit boundary
 134  */
 135 unsigned csum_partial(const unsigned char *buff, unsigned len, unsigned sum)
 136 {
 137         return add32_with_carry(do_csum(buff, len), sum);
 138 }
 139
 140 EXPORT_SYMBOL(csum_partial);
 141
 142 /*
 143  * this routine is used for miscellaneous IP-like checksums, mainly
 144  * in icmp.c
 145  */
 146 unsigned short ip_compute_csum(unsigned char * buff, int len)
 147 {
 148         return csum_fold(csum_partial(buff,len,0));
 149 }
 150 EXPORT_SYMBOL(ip_compute_csum);
 151