minix/lib/liblwip/dist/src/core/inet_chksum.c

   1 /**
   2  * @file
   3  * Incluse internet checksum functions.\n
   4  *
   5  * These are some reference implementations of the checksum algorithm, with the
   6  * aim of being simple, correct and fully portable. Checksumming is the
   7  * first thing you would want to optimize for your platform. If you create
   8  * your own version, link it in and in your cc.h put:
   9  *
  10  * \#define LWIP_CHKSUM your_checksum_routine
  11  *
  12  * Or you can select from the implementations below by defining
  13  * LWIP_CHKSUM_ALGORITHM to 1, 2 or 3.
  14  */
  15
  16 /*
  17  * Copyright (c) 2001-2004 Swedish Institute of Computer Science.
  18  * All rights reserved.
  19  *
  20  * Redistribution and use in source and binary forms, with or without modification,
  21  * are permitted provided that the following conditions are met:
  22  *
  23  * 1. Redistributions of source code must retain the above copyright notice,
  24  *    this list of conditions and the following disclaimer.
  25  * 2. Redistributions in binary form must reproduce the above copyright notice,
  26  *    this list of conditions and the following disclaimer in the documentation
  27  *    and/or other materials provided with the distribution.
  28  * 3. The name of the author may not be used to endorse or promote products
  29  *    derived from this software without specific prior written permission.
  30  *
  31  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
  32  * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
  33  * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
  34  * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  35  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
  36  * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  37  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
  38  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
  39  * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
  40  * OF SUCH DAMAGE.
  41  *
  42  * This file is part of the lwIP TCP/IP stack.
  43  *
  44  * Author: Adam Dunkels <adam@sics.se>
  45  *
  46  */
  47
  48 #include "lwip/opt.h"
  49
  50 #include "lwip/inet_chksum.h"
  51 #include "lwip/def.h"
  52 #include "lwip/ip_addr.h"
  53
  54 #include <string.h>
  55
  56 #ifndef LWIP_CHKSUM
  57 # define LWIP_CHKSUM lwip_standard_chksum
  58 # ifndef LWIP_CHKSUM_ALGORITHM
  59 #  define LWIP_CHKSUM_ALGORITHM 2
  60 # endif
  61 u16_t lwip_standard_chksum(const void *dataptr, int len);
  62 #endif
  63 /* If none set: */
  64 #ifndef LWIP_CHKSUM_ALGORITHM
  65 # define LWIP_CHKSUM_ALGORITHM 0
  66 #endif
  67
  68 #if (LWIP_CHKSUM_ALGORITHM == 1) /* Version #1 */
  69 /**
  70  * lwip checksum
  71  *
  72  * @param dataptr points to start of data to be summed at any boundary
  73  * @param len length of data to be summed
  74  * @return host order (!) lwip checksum (non-inverted Internet sum)
  75  *
  76  * @note accumulator size limits summable length to 64k
  77  * @note host endianess is irrelevant (p3 RFC1071)
  78  */
  79 u16_t
  80 lwip_standard_chksum(const void *dataptr, int len)
  81 {
  82   u32_t acc;
  83   u16_t src;
  84   const u8_t *octetptr;
  85
  86   acc = 0;
  87   /* dataptr may be at odd or even addresses */
  88   octetptr = (const u8_t*)dataptr;
  89   while (len > 1) {
  90     /* declare first octet as most significant
  91        thus assume network order, ignoring host order */
  92     src = (*octetptr) << 8;
  93     octetptr++;
  94     /* declare second octet as least significant */
  95     src |= (*octetptr);
  96     octetptr++;
  97     acc += src;
  98     len -= 2;
  99   }
 100   if (len > 0) {
 101     /* accumulate remaining octet */
 102     src = (*octetptr) << 8;
 103     acc += src;
 104   }
 105   /* add deferred carry bits */
 106   acc = (acc >> 16) + (acc & 0x0000ffffUL);
 107   if ((acc & 0xffff0000UL) != 0) {
 108     acc = (acc >> 16) + (acc & 0x0000ffffUL);
 109   }
 110   /* This maybe a little confusing: reorder sum using lwip_htons()
 111      instead of lwip_ntohs() since it has a little less call overhead.
 112      The caller must invert bits for Internet sum ! */
 113   return lwip_htons((u16_t)acc);
 114 }
 115 #endif
 116
 117 #if (LWIP_CHKSUM_ALGORITHM == 2) /* Alternative version #2 */
 118 /*
 119  * Curt McDowell
 120  * Broadcom Corp.
 121  * csm@broadcom.com
 122  *
 123  * IP checksum two bytes at a time with support for
 124  * unaligned buffer.
 125  * Works for len up to and including 0x20000.
 126  * by Curt McDowell, Broadcom Corp. 12/08/2005
 127  *
 128  * @param dataptr points to start of data to be summed at any boundary
 129  * @param len length of data to be summed
 130  * @return host order (!) lwip checksum (non-inverted Internet sum)
 131  */
 132 u16_t
 133 lwip_standard_chksum(const void *dataptr, int len)
 134 {
 135   const u8_t *pb = (const u8_t *)dataptr;
 136   const u16_t *ps;
 137   u16_t t = 0;
 138   u32_t sum = 0;
 139   int odd = ((mem_ptr_t)pb & 1);
 140
 141   /* Get aligned to u16_t */
 142   if (odd && len > 0) {
 143     ((u8_t *)&t)[1] = *pb++;
 144     len--;
 145   }
 146
 147   /* Add the bulk of the data */
 148   ps = (const u16_t *)(const void *)pb;
 149   while (len > 1) {
 150     sum += *ps++;
 151     len -= 2;
 152   }
 153
 154   /* Consume left-over byte, if any */
 155   if (len > 0) {
 156     ((u8_t *)&t)[0] = *(const u8_t *)ps;
 157   }
 158
 159   /* Add end bytes */
 160   sum += t;
 161
 162   /* Fold 32-bit sum to 16 bits
 163      calling this twice is probably faster than if statements... */
 164   sum = FOLD_U32T(sum);
 165   sum = FOLD_U32T(sum);
 166
 167   /* Swap if alignment was odd */
 168   if (odd) {
 169     sum = SWAP_BYTES_IN_WORD(sum);
 170   }
 171
 172   return (u16_t)sum;
 173 }
 174 #endif
 175
 176 #if (LWIP_CHKSUM_ALGORITHM == 3) /* Alternative version #3 */
 177 /**
 178  * An optimized checksum routine. Basically, it uses loop-unrolling on
 179  * the checksum loop, treating the head and tail bytes specially, whereas
 180  * the inner loop acts on 8 bytes at a time.
 181  *
 182  * @arg start of buffer to be checksummed. May be an odd byte address.
 183  * @len number of bytes in the buffer to be checksummed.
 184  * @return host order (!) lwip checksum (non-inverted Internet sum)
 185  *
 186  * by Curt McDowell, Broadcom Corp. December 8th, 2005
 187  */
 188 u16_t
 189 lwip_standard_chksum(const void *dataptr, int len)
 190 {
 191   const u8_t *pb = (const u8_t *)dataptr;
 192   const u16_t *ps;
 193   u16_t t = 0;
 194   const u32_t *pl;
 195   u32_t sum = 0, tmp;
 196   /* starts at odd byte address? */
 197   int odd = ((mem_ptr_t)pb & 1);
 198
 199   if (odd && len > 0) {
 200     ((u8_t *)&t)[1] = *pb++;
 201     len--;
 202   }
 203
 204   ps = (const u16_t *)(const void*)pb;
 205
 206   if (((mem_ptr_t)ps & 3) && len > 1) {
 207     sum += *ps++;
 208     len -= 2;
 209   }
 210
 211   pl = (const u32_t *)(const void*)ps;
 212
 213   while (len > 7)  {
 214     tmp = sum + *pl++;          /* ping */
 215     if (tmp < sum) {
 216       tmp++;                    /* add back carry */
 217     }
 218
 219     sum = tmp + *pl++;          /* pong */
 220     if (sum < tmp) {
 221       sum++;                    /* add back carry */
 222     }
 223
 224     len -= 8;
 225   }
 226
 227   /* make room in upper bits */
 228   sum = FOLD_U32T(sum);
 229
 230   ps = (const u16_t *)pl;
 231
 232   /* 16-bit aligned word remaining? */
 233   while (len > 1) {
 234     sum += *ps++;
 235     len -= 2;
 236   }
 237
 238   /* dangling tail byte remaining? */
 239   if (len > 0) {                /* include odd byte */
 240     ((u8_t *)&t)[0] = *(const u8_t *)ps;
 241   }
 242
 243   sum += t;                     /* add end bytes */
 244
 245   /* Fold 32-bit sum to 16 bits
 246      calling this twice is probably faster than if statements... */
 247   sum = FOLD_U32T(sum);
 248   sum = FOLD_U32T(sum);
 249
 250   if (odd) {
 251     sum = SWAP_BYTES_IN_WORD(sum);
 252   }
 253
 254   return (u16_t)sum;
 255 }
 256 #endif
 257
 258 /** Parts of the pseudo checksum which are common to IPv4 and IPv6 */
 259 static u16_t
 260 inet_cksum_pseudo_base(struct pbuf *p, u8_t proto, u16_t proto_len, u32_t acc)
 261 {
 262   struct pbuf *q;
 263   u8_t swapped = 0;
 264
 265   /* iterate through all pbuf in chain */
 266   for (q = p; q != NULL; q = q->next) {
 267     LWIP_DEBUGF(INET_DEBUG, ("inet_chksum_pseudo(): checksumming pbuf %p (has next %p) \n",
 268       (void *)q, (void *)q->next));
 269     acc += LWIP_CHKSUM(q->payload, q->len);
 270     /*LWIP_DEBUGF(INET_DEBUG, ("inet_chksum_pseudo(): unwrapped lwip_chksum()=%"X32_F" \n", acc));*/
 271     /* just executing this next line is probably faster that the if statement needed
 272        to check whether we really need to execute it, and does no harm */
 273     acc = FOLD_U32T(acc);
 274     if (q->len % 2 != 0) {
 275       swapped = 1 - swapped;
 276       acc = SWAP_BYTES_IN_WORD(acc);
 277     }
 278     /*LWIP_DEBUGF(INET_DEBUG, ("inet_chksum_pseudo(): wrapped lwip_chksum()=%"X32_F" \n", acc));*/
 279   }
 280
 281   if (swapped) {
 282     acc = SWAP_BYTES_IN_WORD(acc);
 283   }
 284
 285   acc += (u32_t)lwip_htons((u16_t)proto);
 286   acc += (u32_t)lwip_htons(proto_len);
 287
 288   /* Fold 32-bit sum to 16 bits
 289      calling this twice is probably faster than if statements... */
 290   acc = FOLD_U32T(acc);
 291   acc = FOLD_U32T(acc);
 292   LWIP_DEBUGF(INET_DEBUG, ("inet_chksum_pseudo(): pbuf chain lwip_chksum()=%"X32_F"\n", acc));
 293   return (u16_t)~(acc & 0xffffUL);
 294 }
 295
 296 #if LWIP_IPV4
 297 /* inet_chksum_pseudo:
 298  *
 299  * Calculates the IPv4 pseudo Internet checksum used by TCP and UDP for a pbuf chain.
 300  * IP addresses are expected to be in network byte order.
 301  *
 302  * @param p chain of pbufs over that a checksum should be calculated (ip data part)
 303  * @param src source ip address (used for checksum of pseudo header)
 304  * @param dst destination ip address (used for checksum of pseudo header)
 305  * @param proto ip protocol (used for checksum of pseudo header)
 306  * @param proto_len length of the ip data part (used for checksum of pseudo header)
 307  * @return checksum (as u16_t) to be saved directly in the protocol header
 308  */
 309 u16_t
 310 inet_chksum_pseudo(struct pbuf *p, u8_t proto, u16_t proto_len,
 311        const ip4_addr_t *src, const ip4_addr_t *dest)
 312 {
 313   u32_t acc;
 314   u32_t addr;
 315
 316   addr = ip4_addr_get_u32(src);
 317   acc = (addr & 0xffffUL);
 318   acc += ((addr >> 16) & 0xffffUL);
 319   addr = ip4_addr_get_u32(dest);
 320   acc += (addr & 0xffffUL);
 321   acc += ((addr >> 16) & 0xffffUL);
 322   /* fold down to 16 bits */
 323   acc = FOLD_U32T(acc);
 324   acc = FOLD_U32T(acc);
 325
 326   return inet_cksum_pseudo_base(p, proto, proto_len, acc);
 327 }
 328 #endif /* LWIP_IPV4 */
 329
 330 #if LWIP_IPV6
 331 /**
 332  * Calculates the checksum with IPv6 pseudo header used by TCP and UDP for a pbuf chain.
 333  * IPv6 addresses are expected to be in network byte order.
 334  *
 335  * @param p chain of pbufs over that a checksum should be calculated (ip data part)
 336  * @param proto ipv6 protocol/next header (used for checksum of pseudo header)
 337  * @param proto_len length of the ipv6 payload (used for checksum of pseudo header)
 338  * @param src source ipv6 address (used for checksum of pseudo header)
 339  * @param dest destination ipv6 address (used for checksum of pseudo header)
 340  * @return checksum (as u16_t) to be saved directly in the protocol header
 341  */
 342 u16_t
 343 ip6_chksum_pseudo(struct pbuf *p, u8_t proto, u16_t proto_len,
 344        const ip6_addr_t *src, const ip6_addr_t *dest)
 345 {
 346   u32_t acc = 0;
 347   u32_t addr;
 348   u8_t addr_part;
 349
 350   for (addr_part = 0; addr_part < 4; addr_part++) {
 351     addr = src->addr[addr_part];
 352     acc += (addr & 0xffffUL);
 353     acc += ((addr >> 16) & 0xffffUL);
 354     addr = dest->addr[addr_part];
 355     acc += (addr & 0xffffUL);
 356     acc += ((addr >> 16) & 0xffffUL);
 357   }
 358   /* fold down to 16 bits */
 359   acc = FOLD_U32T(acc);
 360   acc = FOLD_U32T(acc);
 361
 362   return inet_cksum_pseudo_base(p, proto, proto_len, acc);
 363 }
 364 #endif /* LWIP_IPV6 */
 365
 366 /* ip_chksum_pseudo:
 367  *
 368  * Calculates the IPv4 or IPv6 pseudo Internet checksum used by TCP and UDP for a pbuf chain.
 369  * IP addresses are expected to be in network byte order.
 370  *
 371  * @param p chain of pbufs over that a checksum should be calculated (ip data part)
 372  * @param src source ip address (used for checksum of pseudo header)
 373  * @param dst destination ip address (used for checksum of pseudo header)
 374  * @param proto ip protocol (used for checksum of pseudo header)
 375  * @param proto_len length of the ip data part (used for checksum of pseudo header)
 376  * @return checksum (as u16_t) to be saved directly in the protocol header
 377  */
 378 u16_t
 379 ip_chksum_pseudo(struct pbuf *p, u8_t proto, u16_t proto_len,
 380        const ip_addr_t *src, const ip_addr_t *dest)
 381 {
 382 #if LWIP_IPV6
 383   if (IP_IS_V6(dest)) {
 384     return ip6_chksum_pseudo(p, proto, proto_len, ip_2_ip6(src), ip_2_ip6(dest));
 385   }
 386 #endif /* LWIP_IPV6 */
 387 #if LWIP_IPV4 && LWIP_IPV6
 388   else
 389 #endif /* LWIP_IPV4 && LWIP_IPV6 */
 390 #if LWIP_IPV4
 391   {
 392     return inet_chksum_pseudo(p, proto, proto_len, ip_2_ip4(src), ip_2_ip4(dest));
 393   }
 394 #endif /* LWIP_IPV4 */
 395 }
 396
 397 /** Parts of the pseudo checksum which are common to IPv4 and IPv6 */
 398 static u16_t
 399 inet_cksum_pseudo_partial_base(struct pbuf *p, u8_t proto, u16_t proto_len,
 400        u16_t chksum_len, u32_t acc)
 401 {
 402   struct pbuf *q;
 403   u8_t swapped = 0;
 404   u16_t chklen;
 405
 406   /* iterate through all pbuf in chain */
 407   for (q = p; (q != NULL) && (chksum_len > 0); q = q->next) {
 408     LWIP_DEBUGF(INET_DEBUG, ("inet_chksum_pseudo(): checksumming pbuf %p (has next %p) \n",
 409       (void *)q, (void *)q->next));
 410     chklen = q->len;
 411     if (chklen > chksum_len) {
 412       chklen = chksum_len;
 413     }
 414     acc += LWIP_CHKSUM(q->payload, chklen);
 415     chksum_len -= chklen;
 416     LWIP_ASSERT("delete me", chksum_len < 0x7fff);
 417     /*LWIP_DEBUGF(INET_DEBUG, ("inet_chksum_pseudo(): unwrapped lwip_chksum()=%"X32_F" \n", acc));*/
 418     /* fold the upper bit down */
 419     acc = FOLD_U32T(acc);
 420     if (q->len % 2 != 0) {
 421       swapped = 1 - swapped;
 422       acc = SWAP_BYTES_IN_WORD(acc);
 423     }
 424     /*LWIP_DEBUGF(INET_DEBUG, ("inet_chksum_pseudo(): wrapped lwip_chksum()=%"X32_F" \n", acc));*/
 425   }
 426
 427   if (swapped) {
 428     acc = SWAP_BYTES_IN_WORD(acc);
 429   }
 430
 431   acc += (u32_t)lwip_htons((u16_t)proto);
 432   acc += (u32_t)lwip_htons(proto_len);
 433
 434   /* Fold 32-bit sum to 16 bits
 435      calling this twice is probably faster than if statements... */
 436   acc = FOLD_U32T(acc);
 437   acc = FOLD_U32T(acc);
 438   LWIP_DEBUGF(INET_DEBUG, ("inet_chksum_pseudo(): pbuf chain lwip_chksum()=%"X32_F"\n", acc));
 439   return (u16_t)~(acc & 0xffffUL);
 440 }
 441
 442 #if LWIP_IPV4
 443 /* inet_chksum_pseudo_partial:
 444  *
 445  * Calculates the IPv4 pseudo Internet checksum used by TCP and UDP for a pbuf chain.
 446  * IP addresses are expected to be in network byte order.
 447  *
 448  * @param p chain of pbufs over that a checksum should be calculated (ip data part)
 449  * @param src source ip address (used for checksum of pseudo header)
 450  * @param dst destination ip address (used for checksum of pseudo header)
 451  * @param proto ip protocol (used for checksum of pseudo header)
 452  * @param proto_len length of the ip data part (used for checksum of pseudo header)
 453  * @return checksum (as u16_t) to be saved directly in the protocol header
 454  */
 455 u16_t
 456 inet_chksum_pseudo_partial(struct pbuf *p, u8_t proto, u16_t proto_len,
 457        u16_t chksum_len, const ip4_addr_t *src, const ip4_addr_t *dest)
 458 {
 459   u32_t acc;
 460   u32_t addr;
 461
 462   addr = ip4_addr_get_u32(src);
 463   acc = (addr & 0xffffUL);
 464   acc += ((addr >> 16) & 0xffffUL);
 465   addr = ip4_addr_get_u32(dest);
 466   acc += (addr & 0xffffUL);
 467   acc += ((addr >> 16) & 0xffffUL);
 468   /* fold down to 16 bits */
 469   acc = FOLD_U32T(acc);
 470   acc = FOLD_U32T(acc);
 471
 472   return inet_cksum_pseudo_partial_base(p, proto, proto_len, chksum_len, acc);
 473 }
 474 #endif /* LWIP_IPV4 */
 475
 476 #if LWIP_IPV6
 477 /**
 478  * Calculates the checksum with IPv6 pseudo header used by TCP and UDP for a pbuf chain.
 479  * IPv6 addresses are expected to be in network byte order. Will only compute for a
 480  * portion of the payload.
 481  *
 482  * @param p chain of pbufs over that a checksum should be calculated (ip data part)
 483  * @param proto ipv6 protocol/next header (used for checksum of pseudo header)
 484  * @param proto_len length of the ipv6 payload (used for checksum of pseudo header)
 485  * @param chksum_len number of payload bytes used to compute chksum
 486  * @param src source ipv6 address (used for checksum of pseudo header)
 487  * @param dest destination ipv6 address (used for checksum of pseudo header)
 488  * @return checksum (as u16_t) to be saved directly in the protocol header
 489  */
 490 u16_t
 491 ip6_chksum_pseudo_partial(struct pbuf *p, u8_t proto, u16_t proto_len,
 492        u16_t chksum_len, const ip6_addr_t *src, const ip6_addr_t *dest)
 493 {
 494   u32_t acc = 0;
 495   u32_t addr;
 496   u8_t addr_part;
 497
 498   for (addr_part = 0; addr_part < 4; addr_part++) {
 499     addr = src->addr[addr_part];
 500     acc += (addr & 0xffffUL);
 501     acc += ((addr >> 16) & 0xffffUL);
 502     addr = dest->addr[addr_part];
 503     acc += (addr & 0xffffUL);
 504     acc += ((addr >> 16) & 0xffffUL);
 505   }
 506   /* fold down to 16 bits */
 507   acc = FOLD_U32T(acc);
 508   acc = FOLD_U32T(acc);
 509
 510   return inet_cksum_pseudo_partial_base(p, proto, proto_len, chksum_len, acc);
 511 }
 512 #endif /* LWIP_IPV6 */
 513
 514 /* ip_chksum_pseudo_partial:
 515  *
 516  * Calculates the IPv4 or IPv6 pseudo Internet checksum used by TCP and UDP for a pbuf chain.
 517  *
 518  * @param p chain of pbufs over that a checksum should be calculated (ip data part)
 519  * @param src source ip address (used for checksum of pseudo header)
 520  * @param dst destination ip address (used for checksum of pseudo header)
 521  * @param proto ip protocol (used for checksum of pseudo header)
 522  * @param proto_len length of the ip data part (used for checksum of pseudo header)
 523  * @return checksum (as u16_t) to be saved directly in the protocol header
 524  */
 525 u16_t
 526 ip_chksum_pseudo_partial(struct pbuf *p, u8_t proto, u16_t proto_len,
 527        u16_t chksum_len, const ip_addr_t *src, const ip_addr_t *dest)
 528 {
 529 #if LWIP_IPV6
 530   if (IP_IS_V6(dest)) {
 531     return ip6_chksum_pseudo_partial(p, proto, proto_len, chksum_len, ip_2_ip6(src), ip_2_ip6(dest));
 532   }
 533 #endif /* LWIP_IPV6 */
 534 #if LWIP_IPV4 && LWIP_IPV6
 535   else
 536 #endif /* LWIP_IPV4 && LWIP_IPV6 */
 537 #if LWIP_IPV4
 538   {
 539     return inet_chksum_pseudo_partial(p, proto, proto_len, chksum_len, ip_2_ip4(src), ip_2_ip4(dest));
 540   }
 541 #endif /* LWIP_IPV4 */
 542 }
 543
 544 /* inet_chksum:
 545  *
 546  * Calculates the Internet checksum over a portion of memory. Used primarily for IP
 547  * and ICMP.
 548  *
 549  * @param dataptr start of the buffer to calculate the checksum (no alignment needed)
 550  * @param len length of the buffer to calculate the checksum
 551  * @return checksum (as u16_t) to be saved directly in the protocol header
 552  */
 553
 554 u16_t
 555 inet_chksum(const void *dataptr, u16_t len)
 556 {
 557   return (u16_t)~(unsigned int)LWIP_CHKSUM(dataptr, len);
 558 }
 559
 560 /**
 561  * Calculate a checksum over a chain of pbufs (without pseudo-header, much like
 562  * inet_chksum only pbufs are used).
 563  *
 564  * @param p pbuf chain over that the checksum should be calculated
 565  * @return checksum (as u16_t) to be saved directly in the protocol header
 566  */
 567 u16_t
 568 inet_chksum_pbuf(struct pbuf *p)
 569 {
 570   u32_t acc;
 571   struct pbuf *q;
 572   u8_t swapped;
 573
 574   acc = 0;
 575   swapped = 0;
 576   for (q = p; q != NULL; q = q->next) {
 577     acc += LWIP_CHKSUM(q->payload, q->len);
 578     acc = FOLD_U32T(acc);
 579     if (q->len % 2 != 0) {
 580       swapped = 1 - swapped;
 581       acc = SWAP_BYTES_IN_WORD(acc);
 582     }
 583   }
 584
 585   if (swapped) {
 586     acc = SWAP_BYTES_IN_WORD(acc);
 587   }
 588   return (u16_t)~(acc & 0xffffUL);
 589 }
 590
 591 /* These are some implementations for LWIP_CHKSUM_COPY, which copies data
 592  * like MEMCPY but generates a checksum at the same time. Since this is a
 593  * performance-sensitive function, you might want to create your own version
 594  * in assembly targeted at your hardware by defining it in lwipopts.h:
 595  *   #define LWIP_CHKSUM_COPY(dst, src, len) your_chksum_copy(dst, src, len)
 596  */
 597
 598 #if (LWIP_CHKSUM_COPY_ALGORITHM == 1) /* Version #1 */
 599 /** Safe but slow: first call MEMCPY, then call LWIP_CHKSUM.
 600  * For architectures with big caches, data might still be in cache when
 601  * generating the checksum after copying.
 602  */
 603 u16_t
 604 lwip_chksum_copy(void *dst, const void *src, u16_t len)
 605 {
 606   MEMCPY(dst, src, len);
 607   return LWIP_CHKSUM(dst, len);
 608 }
 609 #endif /* (LWIP_CHKSUM_COPY_ALGORITHM == 1) */