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Linux/arch/x86/lib/csum-partial_64.c

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  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             : "" (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 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),  "" (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 }
147 EXPORT_SYMBOL(ip_compute_csum);
148 
149 

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