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 static 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  */
  34 static 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 upto 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 EXPORT_SYMBOL(csum_partial);
 140
 141 /*
 142  * this routine is used for miscellaneous IP-like checksums, mainly
 143  * in icmp.c
 144  */
 145 __sum16 ip_compute_csum(const void *buff, int len)
 146 {
 147         return csum_fold(csum_partial(buff,len,0));
 148 }
 149 EXPORT_SYMBOL(ip_compute_csum);
 150