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

   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
  13static 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 */
  35static 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}
 139EXPORT_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}
 149EXPORT_SYMBOL(ip_compute_csum);
 150
 151