1/* 2 * INET An implementation of the TCP/IP protocol suite for the LINUX 3 * operating system. INET is implemented using the BSD Socket 4 * interface as the means of communication with the user level. 5 * 6 * IP/TCP/UDP checksumming routines 7 * 8 * Authors: Jorge Cwik, <jorge@laser.satlink.net> 9 * Arnt Gulbrandsen, <agulbra@nvg.unit.no> 10 * Tom May, <ftom@netcom.com> 11 * Andreas Schwab, <schwab@issan.informatik.uni-dortmund.de> 12 * Lots of code moved from tcp.c and ip.c; see those files 13 * for more names. 14 * 15 * 03/02/96 Jes Sorensen, Andreas Schwab, Roman Hodek: 16 * Fixed some nasty bugs, causing some horrible crashes. 17 * A: At some points, the sum (%0) was used as 18 * length-counter instead of the length counter 19 * (%1). Thanks to Roman Hodek for pointing this out. 20 * B: GCC seems to mess up if one uses too many 21 * data-registers to hold input values and one tries to 22 * specify d0 and d1 as scratch registers. Letting gcc choose these 23 * registers itself solves the problem. 24 * 25 * This program is free software; you can redistribute it and/or 26 * modify it under the terms of the GNU General Public License 27 * as published by the Free Software Foundation; either version 28 * 2 of the License, or (at your option) any later version. 29 */ 30 31/* Revised by Kenneth Albanowski for m68knommu. Basic problem: unaligned access kills, so most 32 of the assembly has to go. */ 33 34#include <net/checksum.h> 35#include <linux/module.h> 36 37static inline unsigned short from32to16(unsigned long x) 38{ 39 /* add up 16-bit and 16-bit for 16+c bit */ 40 x = (x & 0xffff) + (x >> 16); 41 /* add up carry.. */ 42 x = (x & 0xffff) + (x >> 16); 43 return x; 44} 45 46static unsigned long do_csum(const unsigned char * buff, int len) 47{ 48 int odd, count; 49 unsigned long result = 0; 50 51 if (len <= 0) 52 goto out; 53 odd = 1 & (unsigned long) buff; 54 if (odd) { 55 result = *buff; 56 len--; 57 buff++; 58 } 59 count = len >> 1; /* nr of 16-bit words.. */ 60 if (count) { 61 if (2 & (unsigned long) buff) { 62 result += *(unsigned short *) buff; 63 count--; 64 len -= 2; 65 buff += 2; 66 } 67 count >>= 1; /* nr of 32-bit words.. */ 68 if (count) { 69 unsigned long carry = 0; 70 do { 71 unsigned long w = *(unsigned long *) buff; 72 count--; 73 buff += 4; 74 result += carry; 75 result += w; 76 carry = (w > result); 77 } while (count); 78 result += carry; 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 += (*buff << 8); 88 result = from32to16(result); 89 if (odd) 90 result = ((result >> 8) & 0xff) | ((result & 0xff) << 8); 91out: 92 return result; 93} 94 95/* 96 * This is a version of ip_compute_csum() optimized for IP headers, 97 * which always checksum on 4 octet boundaries. 98 */ 99__sum16 ip_fast_csum(const void *iph, unsigned int ihl) 100{ 101 return (__force __sum16)~do_csum(iph,ihl*4); 102} 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/* 117 * Egads... That thing apparently assumes that *all* checksums it ever sees will 118 * be folded. Very likely a bug. 119 */ 120__wsum csum_partial(const void *buff, int len, __wsum sum) 121{ 122 unsigned int result = do_csum(buff, len); 123 124 /* add in old sum, and carry.. */ 125 result += (__force u32)sum; 126 /* 16+c bits -> 16 bits */ 127 result = (result & 0xffff) + (result >> 16); 128 return (__force __wsum)result; 129} 130 131EXPORT_SYMBOL(csum_partial); 132 133/* 134 * this routine is used for miscellaneous IP-like checksums, mainly 135 * in icmp.c 136 */ 137__sum16 ip_compute_csum(const void *buff, int len) 138{ 139 return (__force __sum16)~do_csum(buff,len); 140} 141 142/* 143 * copy from fs while checksumming, otherwise like csum_partial 144 */ 145 146__wsum 147csum_partial_copy_from_user(const void __user *src, void *dst, int len, 148 __wsum sum, int *csum_err) 149{ 150 if (csum_err) *csum_err = 0; 151 memcpy(dst, (__force const void *)src, len); 152 return csum_partial(dst, len, sum); 153} 154 155/* 156 * copy from ds while checksumming, otherwise like csum_partial 157 */ 158 159__wsum 160csum_partial_copy_nocheck(const void *src, void *dst, int len, __wsum sum) 161{ 162 memcpy(dst, src, len); 163 return csum_partial(dst, len, sum); 164} 165