1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * Network Checksum & Copy routine
4  *
5  * Copyright (C) 1999, 2003-2004 Hewlett-Packard Co
6  *	Stephane Eranian <eranian@hpl.hp.com>
7  *
8  * Most of the code has been imported from Linux/Alpha
9  */
10 
11 #include <linux/module.h>
12 #include <linux/types.h>
13 #include <linux/string.h>
14 
15 #include <net/checksum.h>
16 
17 /*
18  * XXX Fixme: those 2 inlines are meant for debugging and will go away
19  */
20 static inline unsigned
21 short from64to16(unsigned long x)
22 {
23 	/* add up 32-bit words for 33 bits */
24 	x = (x & 0xffffffff) + (x >> 32);
25 	/* add up 16-bit and 17-bit words for 17+c bits */
26 	x = (x & 0xffff) + (x >> 16);
27 	/* add up 16-bit and 2-bit for 16+c bit */
28 	x = (x & 0xffff) + (x >> 16);
29 	/* add up carry.. */
30 	x = (x & 0xffff) + (x >> 16);
31 	return x;
32 }
33 
34 static inline
35 unsigned long do_csum_c(const unsigned char * buff, int len, unsigned int psum)
36 {
37 	int odd, count;
38 	unsigned long result = (unsigned long)psum;
39 
40 	if (len <= 0)
41 		goto out;
42 	odd = 1 & (unsigned long) buff;
43 	if (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 			if (4 & (unsigned long) buff) {
59 				result += *(unsigned int *) buff;
60 				count--;
61 				len -= 4;
62 				buff += 4;
63 			}
64 			count >>= 1;	/* nr of 64-bit words.. */
65 			if (count) {
66 				unsigned long carry = 0;
67 				do {
68 					unsigned long w = *(unsigned long *) buff;
69 					count--;
70 					buff += 8;
71 					result += carry;
72 					result += w;
73 					carry = (w > result);
74 				} while (count);
75 				result += carry;
76 				result = (result & 0xffffffff) + (result >> 32);
77 			}
78 			if (len & 4) {
79 				result += *(unsigned int *) buff;
80 				buff += 4;
81 			}
82 		}
83 		if (len & 2) {
84 			result += *(unsigned short *) buff;
85 			buff += 2;
86 		}
87 	}
88 	if (len & 1)
89 		result += *buff;
90 
91 	result = from64to16(result);
92 
93 	if (odd)
94 		result = ((result >> 8) & 0xff) | ((result & 0xff) << 8);
95 
96 out:
97 	return result;
98 }
99