arch/x86/lib/csum-partial_64.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * arch/x86_64/lib/csum-partial.c
   4  *
   5  * This file contains network checksum routines that are better done
   6  * in an architecture-specific manner due to speed.
   7  */
   8
   9 #include <linux/compiler.h>
  10 #include <linux/export.h>
  11 #include <asm/checksum.h>
  12
  13 static inline unsigned short from32to16(unsigned a)
  14 {
  15         unsigned short b = a >> 16;
  16         asm("addw %w2,%w0\n\t"
  17             "adcw $0,%w0\n"
  18             : "=r" (b)
  19             : "0" (b), "r" (a));
  20         return b;
  21 }
  22
  23 /*
  24  * Do a 64-bit checksum on an arbitrary memory area.
  25  * Returns a 32bit checksum.
  26  *
  27  * This isn't as time critical as it used to be because many NICs
  28  * do hardware checksumming these days.
  29  *
  30  * Things tried and found to not make it faster:
  31  * Manual Prefetching
  32  * Unrolling to an 128 bytes inner loop.
  33  * Using interleaving with more registers to break the carry chains.
  34  */
  35 static unsigned do_csum(const unsigned char *buff, unsigned len)
  36 {
  37         unsigned odd, count;
  38         unsigned long result = 0;
  39
  40         if (unlikely(len == 0))
  41                 return result;
  42         odd = 1 & (unsigned long) buff;
  43         if (unlikely(odd)) {
  44                 result = *buff << 8;
  45                 len--;
  46                 buff++;
  47         }
  48         count = len >> 1;               /* nr of 16-bit words.. */
  49         if (count) {
  50                 if (2 & (unsigned long) buff) {
  51                         result += *(unsigned short *)buff;
  52                         count--;
  53                         len -= 2;
  54                         buff += 2;
  55                 }
  56                 count >>= 1;            /* nr of 32-bit words.. */
  57                 if (count) {
  58                         unsigned long zero;
  59                         unsigned count64;
  60                         if (4 & (unsigned long) buff) {
  61                                 result += *(unsigned int *) buff;
  62                                 count--;
  63                                 len -= 4;
  64                                 buff += 4;
  65                         }
  66                         count >>= 1;    /* nr of 64-bit words.. */
  67
  68                         /* main loop using 64byte blocks */
  69                         zero = 0;
  70                         count64 = count >> 3;
  71                         while (count64) {
  72                                 asm("addq 0*8(%[src]),%[res]\n\t"
  73                                     "adcq 1*8(%[src]),%[res]\n\t"
  74                                     "adcq 2*8(%[src]),%[res]\n\t"
  75                                     "adcq 3*8(%[src]),%[res]\n\t"
  76                                     "adcq 4*8(%[src]),%[res]\n\t"
  77                                     "adcq 5*8(%[src]),%[res]\n\t"
  78                                     "adcq 6*8(%[src]),%[res]\n\t"
  79                                     "adcq 7*8(%[src]),%[res]\n\t"
  80                                     "adcq %[zero],%[res]"
  81                                     : [res] "=r" (result)
  82                                     : [src] "r" (buff), [zero] "r" (zero),
  83                                     "[res]" (result));
  84                                 buff += 64;
  85                                 count64--;
  86                         }
  87
  88                         /* last up to 7 8byte blocks */
  89                         count %= 8;
  90                         while (count) {
  91                                 asm("addq %1,%0\n\t"
  92                                     "adcq %2,%0\n"
  93                                             : "=r" (result)
  94                                     : "m" (*(unsigned long *)buff),
  95                                     "r" (zero),  "0" (result));
  96                                 --count;
  97                                 buff += 8;
  98                         }
  99                         result = add32_with_carry(result>>32,
 100                                                   result&0xffffffff);
 101
 102                         if (len & 4) {
 103                                 result += *(unsigned int *) buff;
 104                                 buff += 4;
 105                         }
 106                 }
 107                 if (len & 2) {
 108                         result += *(unsigned short *) buff;
 109                         buff += 2;
 110                 }
 111         }
 112         if (len & 1)
 113                 result += *buff;
 114         result = add32_with_carry(result>>32, result & 0xffffffff);
 115         if (unlikely(odd)) {
 116                 result = from32to16(result);
 117                 result = ((result >> 8) & 0xff) | ((result & 0xff) << 8);
 118         }
 119         return result;
 120 }
 121
 122 /*
 123  * computes the checksum of a memory block at buff, length len,
 124  * and adds in "sum" (32-bit)
 125  *
 126  * returns a 32-bit number suitable for feeding into itself
 127  * or csum_tcpudp_magic
 128  *
 129  * this function must be called with even lengths, except
 130  * for the last fragment, which may be odd
 131  *
 132  * it's best to have buff aligned on a 64-bit boundary
 133  */
 134 __wsum csum_partial(const void *buff, int len, __wsum sum)
 135 {
 136         return (__force __wsum)add32_with_carry(do_csum(buff, len),
 137                                                 (__force u32)sum);
 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