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 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), "" (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
151
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