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#include <asm/word-at-a-time.h>
13
14static inline __wsum csum_finalize_sum(u64 temp64)
15{
16 return (__force __wsum)((temp64 + ror64(word: temp64, shift: 32)) >> 32);
17}
18
19static inline unsigned long update_csum_40b(unsigned long sum, const unsigned long m[5])
20{
21 asm("addq %1,%0\n\t"
22 "adcq %2,%0\n\t"
23 "adcq %3,%0\n\t"
24 "adcq %4,%0\n\t"
25 "adcq %5,%0\n\t"
26 "adcq $0,%0"
27 :"+r" (sum)
28 :"m" (m[0]), "m" (m[1]), "m" (m[2]),
29 "m" (m[3]), "m" (m[4]));
30 return sum;
31}
32
33/*
34 * Do a checksum on an arbitrary memory area.
35 * Returns a 32bit checksum.
36 *
37 * This isn't as time critical as it used to be because many NICs
38 * do hardware checksumming these days.
39 *
40 * Still, with CHECKSUM_COMPLETE this is called to compute
41 * checksums on IPv6 headers (40 bytes) and other small parts.
42 * it's best to have buff aligned on a 64-bit boundary
43 */
44__wsum csum_partial(const void *buff, int len, __wsum sum)
45{
46 u64 temp64 = (__force u64)sum;
47
48 /* Do two 40-byte chunks in parallel to get better ILP */
49 if (likely(len >= 80)) {
50 u64 temp64_2 = 0;
51 do {
52 temp64 = update_csum_40b(sum: temp64, m: buff);
53 temp64_2 = update_csum_40b(sum: temp64_2, m: buff + 40);
54 buff += 80;
55 len -= 80;
56 } while (len >= 80);
57
58 asm("addq %1,%0\n\t"
59 "adcq $0,%0"
60 :"+r" (temp64): "r" (temp64_2));
61 }
62
63 /*
64 * len == 40 is the hot case due to IPv6 headers, so return
65 * early for that exact case without checking the tail bytes.
66 */
67 if (len >= 40) {
68 temp64 = update_csum_40b(sum: temp64, m: buff);
69 len -= 40;
70 if (!len)
71 return csum_finalize_sum(temp64);
72 buff += 40;
73 }
74
75 if (len & 32) {
76 asm("addq 0*8(%[src]),%[res]\n\t"
77 "adcq 1*8(%[src]),%[res]\n\t"
78 "adcq 2*8(%[src]),%[res]\n\t"
79 "adcq 3*8(%[src]),%[res]\n\t"
80 "adcq $0,%[res]"
81 : [res] "+r"(temp64)
82 : [src] "r"(buff), "m"(*(const char(*)[32])buff));
83 buff += 32;
84 }
85 if (len & 16) {
86 asm("addq 0*8(%[src]),%[res]\n\t"
87 "adcq 1*8(%[src]),%[res]\n\t"
88 "adcq $0,%[res]"
89 : [res] "+r"(temp64)
90 : [src] "r"(buff), "m"(*(const char(*)[16])buff));
91 buff += 16;
92 }
93 if (len & 8) {
94 asm("addq 0*8(%[src]),%[res]\n\t"
95 "adcq $0,%[res]"
96 : [res] "+r"(temp64)
97 : [src] "r"(buff), "m"(*(const char(*)[8])buff));
98 buff += 8;
99 }
100 if (len & 7) {
101 unsigned int shift = (-len << 3) & 63;
102 unsigned long trail;
103
104 trail = (load_unaligned_zeropad(addr: buff) << shift) >> shift;
105
106 asm("addq %[trail],%[res]\n\t"
107 "adcq $0,%[res]"
108 : [res] "+r"(temp64)
109 : [trail] "r"(trail));
110 }
111 return csum_finalize_sum(temp64);
112}
113EXPORT_SYMBOL(csum_partial);
114
115/*
116 * this routine is used for miscellaneous IP-like checksums, mainly
117 * in icmp.c
118 */
119__sum16 ip_compute_csum(const void *buff, int len)
120{
121 return csum_fold(csum: csum_partial(buff, len, 0));
122}
123EXPORT_SYMBOL(ip_compute_csum);
124

source code of linux/arch/x86/lib/csum-partial_64.c