1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * INET		An implementation of the TCP/IP protocol suite for the LINUX
4 *		operating system.  INET is implemented using the  BSD Socket
5 *		interface as the means of communication with the user level.
6 *
7 *		MIPS specific IP/TCP/UDP checksumming routines
8 *
9 * Authors:	Ralf Baechle, <ralf@waldorf-gmbh.de>
10 *		Lots of code moved from tcp.c and ip.c; see those files
11 *		for more names.
12 */
13#include <linux/module.h>
14#include <linux/types.h>
15
16#include <net/checksum.h>
17#include <asm/byteorder.h>
18#include <asm/string.h>
19#include <linux/uaccess.h>
20
21#define addc(_t,_r)                     \
22	__asm__ __volatile__ (          \
23"       add             %0, %1, %0\n"   \
24"       addc            %0, %%r0, %0\n" \
25	: "=r"(_t)                      \
26	: "r"(_r), "0"(_t));
27
28static inline unsigned short from32to16(unsigned int x)
29{
30	/* 32 bits --> 16 bits + carry */
31	x = (x & 0xffff) + (x >> 16);
32	/* 16 bits + carry --> 16 bits including carry */
33	x = (x & 0xffff) + (x >> 16);
34	return (unsigned short)x;
35}
36
37static inline unsigned int do_csum(const unsigned char * buff, int len)
38{
39	int odd, count;
40	unsigned int result = 0;
41
42	if (len <= 0)
43		goto out;
44	odd = 1 & (unsigned long) buff;
45	if (odd) {
46		result = be16_to_cpu(*buff);
47		len--;
48		buff++;
49	}
50	count = len >> 1;		/* nr of 16-bit words.. */
51	if (count) {
52		if (2 & (unsigned long) buff) {
53			result += *(unsigned short *) buff;
54			count--;
55			len -= 2;
56			buff += 2;
57		}
58		count >>= 1;		/* nr of 32-bit words.. */
59		if (count) {
60			while (count >= 4) {
61				unsigned int r1, r2, r3, r4;
62				r1 = *(unsigned int *)(buff + 0);
63				r2 = *(unsigned int *)(buff + 4);
64				r3 = *(unsigned int *)(buff + 8);
65				r4 = *(unsigned int *)(buff + 12);
66				addc(result, r1);
67				addc(result, r2);
68				addc(result, r3);
69				addc(result, r4);
70				count -= 4;
71				buff += 16;
72			}
73			while (count) {
74				unsigned int w = *(unsigned int *) buff;
75				count--;
76				buff += 4;
77				addc(result, w);
78			}
79			result = (result & 0xffff) + (result >> 16);
80		}
81		if (len & 2) {
82			result += *(unsigned short *) buff;
83			buff += 2;
84		}
85	}
86	if (len & 1)
87		result += le16_to_cpu(*buff);
88	result = from32to16(result);
89	if (odd)
90		result = swab16(result);
91out:
92	return result;
93}
94
95/*
96 * computes a partial checksum, e.g. for TCP/UDP fragments
97 */
98/*
99 * why bother folding?
100 */
101__wsum csum_partial(const void *buff, int len, __wsum sum)
102{
103	unsigned int result = do_csum(buff, len);
104	addc(result, sum);
105	return (__force __wsum)from32to16(result);
106}
107
108EXPORT_SYMBOL(csum_partial);
109