checksum.c

  1// SPDX-License-Identifier: GPL-2.0-or-later
  2/*
  3 *
  4 * INET		An implementation of the TCP/IP protocol suite for the LINUX
  5 *		operating system.  INET is implemented using the  BSD Socket
  6 *		interface as the means of communication with the user level.
  7 *
  8 *		IP/TCP/UDP checksumming routines
  9 *
 10 * Authors:	Jorge Cwik, <jorge@laser.satlink.net>
 11 *		Arnt Gulbrandsen, <agulbra@nvg.unit.no>
 12 *		Tom May, <ftom@netcom.com>
 13 *		Andreas Schwab, <schwab@issan.informatik.uni-dortmund.de>
 14 *		Lots of code moved from tcp.c and ip.c; see those files
 15 *		for more names.
 16 *
 17 * 03/02/96	Jes Sorensen, Andreas Schwab, Roman Hodek:
 18 *		Fixed some nasty bugs, causing some horrible crashes.
 19 *		A: At some points, the sum (%0) was used as
 20 *		length-counter instead of the length counter
 21 *		(%1). Thanks to Roman Hodek for pointing this out.
 22 *		B: GCC seems to mess up if one uses too many
 23 *		data-registers to hold input values and one tries to
 24 *		specify d0 and d1 as scratch registers. Letting gcc
 25 *		choose these registers itself solves the problem.
 26 */
 27
 28/* Revised by Kenneth Albanowski for m68knommu. Basic problem: unaligned access
 29 kills, so most of the assembly has to go. */
 30
 31#include <linux/export.h>
 32#include <net/checksum.h>
 33
 34#include <asm/byteorder.h>
 35
 36#ifndef do_csum
 37static unsigned int do_csum(const unsigned char *buff, int len)
 38{
 39	int odd;
 40	unsigned int result = 0;
 41
 42	if (len <= 0)
 43		goto out;
 44	odd = 1 & (unsigned long) buff;
 45	if (odd) {
 46#ifdef __LITTLE_ENDIAN
 47		result += (*buff << 8);
 48#else
 49		result = *buff;
 50#endif
 51		len--;
 52		buff++;
 53	}
 54	if (len >= 2) {
 55		if (2 & (unsigned long) buff) {
 56			result += *(unsigned short *) buff;
 57			len -= 2;
 58			buff += 2;
 59		}
 60		if (len >= 4) {
 61			const unsigned char *end = buff + ((unsigned)len & ~3);
 62			unsigned int carry = 0;
 63			do {
 64				unsigned int w = *(unsigned int *) buff;
 65				buff += 4;
 66				result += carry;
 67				result += w;
 68				carry = (w > result);
 69			} while (buff < end);
 70			result += carry;
 71			result = (result & 0xffff) + (result >> 16);
 72		}
 73		if (len & 2) {
 74			result += *(unsigned short *) buff;
 75			buff += 2;
 76		}
 77	}
 78	if (len & 1)
 79#ifdef __LITTLE_ENDIAN
 80		result += *buff;
 81#else
 82		result += (*buff << 8);
 83#endif
 84	result = csum_from32to16(result);
 85	if (odd)
 86		result = ((result >> 8) & 0xff) | ((result & 0xff) << 8);
 87out:
 88	return result;
 89}
 90#endif
 91
 92#ifndef ip_fast_csum
 93/*
 94 *	This is a version of ip_compute_csum() optimized for IP headers,
 95 *	which always checksum on 4 octet boundaries.
 96 */
 97__sum16 ip_fast_csum(const void *iph, unsigned int ihl)
 98{
 99	return (__force __sum16)~do_csum(iph, ihl*4);
100}
101EXPORT_SYMBOL(ip_fast_csum);
102#endif
103
104/*
105 * computes the checksum of a memory block at buff, length len,
106 * and adds in "sum" (32-bit)
107 *
108 * returns a 32-bit number suitable for feeding into itself
109 * or csum_tcpudp_magic
110 *
111 * this function must be called with even lengths, except
112 * for the last fragment, which may be odd
113 *
114 * it's best to have buff aligned on a 32-bit boundary
115 */
116__wsum csum_partial(const void *buff, int len, __wsum wsum)
117{
118	unsigned int sum = (__force unsigned int)wsum;
119	unsigned int result = do_csum(buff, len);
120
121	/* add in old sum, and carry.. */
122	result += sum;
123	if (sum > result)
124		result += 1;
125	return (__force __wsum)result;
126}
127EXPORT_SYMBOL(csum_partial);
128
129/*
130 * this routine is used for miscellaneous IP-like checksums, mainly
131 * in icmp.c
132 */
133__sum16 ip_compute_csum(const void *buff, int len)
134{
135	return (__force __sum16)~do_csum(buff, len);
136}
137EXPORT_SYMBOL(ip_compute_csum);
138
139#ifndef csum_tcpudp_nofold
140static inline u32 from64to32(u64 x)
141{
142	/* add up 32-bit and 32-bit for 32+c bit */
143	x = (x & 0xffffffff) + (x >> 32);
144	/* add up carry.. */
145	x = (x & 0xffffffff) + (x >> 32);
146	return (u32)x;
147}
148
149__wsum csum_tcpudp_nofold(__be32 saddr, __be32 daddr,
150			  __u32 len, __u8 proto, __wsum sum)
151{
152	unsigned long long s = (__force u32)sum;
153
154	s += (__force u32)saddr;
155	s += (__force u32)daddr;
156#ifdef __BIG_ENDIAN
157	s += proto + len;
158#else
159	s += (proto + len) << 8;
160#endif
161	return (__force __wsum)from64to32(s);
162}
163EXPORT_SYMBOL(csum_tcpudp_nofold);
164#endif