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