lib/string.c

   1 /*
   2  *  linux/lib/string.c
   3  *
   4  *  Copyright (C) 1991, 1992  Linus Torvalds
   5  */
   6
   7 /*
   8  * stupid library routines.. The optimized versions should generally be found
   9  * as inline code in <asm-xx/string.h>
  10  *
  11  * These are buggy as well..
  12  *
  13  * * Fri Jun 25 1999, Ingo Oeser <ioe@informatik.tu-chemnitz.de>
  14  * -  Added strsep() which will replace strtok() soon (because strsep() is
  15  *    reentrant and should be faster). Use only strsep() in new code, please.
  16  *
  17  * * Sat Feb 09 2002, Jason Thomas <jason@topic.com.au>,
  18  *                    Matthew Hawkins <matt@mh.dropbear.id.au>
  19  * -  Kissed strtok() goodbye
  20  */
  21
  22 #include <linux/types.h>
  23 #include <linux/string.h>
  24 #include <linux/ctype.h>
  25 #include <linux/kernel.h>
  26 #include <linux/export.h>
  27 #include <linux/bug.h>
  28 #include <linux/errno.h>
  29
  30 #ifndef __HAVE_ARCH_STRNCASECMP
  31 /**
  32  * strncasecmp - Case insensitive, length-limited string comparison
  33  * @s1: One string
  34  * @s2: The other string
  35  * @len: the maximum number of characters to compare
  36  */
  37 int strncasecmp(const char *s1, const char *s2, size_t len)
  38 {
  39         /* Yes, Virginia, it had better be unsigned */
  40         unsigned char c1, c2;
  41
  42         if (!len)
  43                 return 0;
  44
  45         do {
  46                 c1 = *s1++;
  47                 c2 = *s2++;
  48                 if (!c1 || !c2)
  49                         break;
  50                 if (c1 == c2)
  51                         continue;
  52                 c1 = tolower(c1);
  53                 c2 = tolower(c2);
  54                 if (c1 != c2)
  55                         break;
  56         } while (--len);
  57         return (int)c1 - (int)c2;
  58 }
  59 EXPORT_SYMBOL(strncasecmp);
  60 #endif
  61 #ifndef __HAVE_ARCH_STRNICMP
  62 #undef strnicmp
  63 int strnicmp(const char *s1, const char *s2, size_t len)
  64 {
  65         return strncasecmp(s1, s2, len);
  66 }
  67 EXPORT_SYMBOL(strnicmp);
  68 #endif
  69
  70 #ifndef __HAVE_ARCH_STRCASECMP
  71 int strcasecmp(const char *s1, const char *s2)
  72 {
  73         int c1, c2;
  74
  75         do {
  76                 c1 = tolower(*s1++);
  77                 c2 = tolower(*s2++);
  78         } while (c1 == c2 && c1 != 0);
  79         return c1 - c2;
  80 }
  81 EXPORT_SYMBOL(strcasecmp);
  82 #endif
  83
  84 #ifndef __HAVE_ARCH_STRCPY
  85 /**
  86  * strcpy - Copy a %NUL terminated string
  87  * @dest: Where to copy the string to
  88  * @src: Where to copy the string from
  89  */
  90 #undef strcpy
  91 char *strcpy(char *dest, const char *src)
  92 {
  93         char *tmp = dest;
  94
  95         while ((*dest++ = *src++) != '\0')
  96                 /* nothing */;
  97         return tmp;
  98 }
  99 EXPORT_SYMBOL(strcpy);
 100 #endif
 101
 102 #ifndef __HAVE_ARCH_STRNCPY
 103 /**
 104  * strncpy - Copy a length-limited, C-string
 105  * @dest: Where to copy the string to
 106  * @src: Where to copy the string from
 107  * @count: The maximum number of bytes to copy
 108  *
 109  * The result is not %NUL-terminated if the source exceeds
 110  * @count bytes.
 111  *
 112  * In the case where the length of @src is less than  that  of
 113  * count, the remainder of @dest will be padded with %NUL.
 114  *
 115  */
 116 char *strncpy(char *dest, const char *src, size_t count)
 117 {
 118         char *tmp = dest;
 119
 120         while (count) {
 121                 if ((*tmp = *src) != 0)
 122                         src++;
 123                 tmp++;
 124                 count--;
 125         }
 126         return dest;
 127 }
 128 EXPORT_SYMBOL(strncpy);
 129 #endif
 130
 131 #ifndef __HAVE_ARCH_STRLCPY
 132 /**
 133  * strlcpy - Copy a C-string into a sized buffer
 134  * @dest: Where to copy the string to
 135  * @src: Where to copy the string from
 136  * @size: size of destination buffer
 137  *
 138  * Compatible with *BSD: the result is always a valid
 139  * NUL-terminated string that fits in the buffer (unless,
 140  * of course, the buffer size is zero). It does not pad
 141  * out the result like strncpy() does.
 142  */
 143 size_t strlcpy(char *dest, const char *src, size_t size)
 144 {
 145         size_t ret = strlen(src);
 146
 147         if (size) {
 148                 size_t len = (ret >= size) ? size - 1 : ret;
 149                 memcpy(dest, src, len);
 150                 dest[len] = '\0';
 151         }
 152         return ret;
 153 }
 154 EXPORT_SYMBOL(strlcpy);
 155 #endif
 156
 157 #ifndef __HAVE_ARCH_STRCAT
 158 /**
 159  * strcat - Append one %NUL-terminated string to another
 160  * @dest: The string to be appended to
 161  * @src: The string to append to it
 162  */
 163 #undef strcat
 164 char *strcat(char *dest, const char *src)
 165 {
 166         char *tmp = dest;
 167
 168         while (*dest)
 169                 dest++;
 170         while ((*dest++ = *src++) != '\0')
 171                 ;
 172         return tmp;
 173 }
 174 EXPORT_SYMBOL(strcat);
 175 #endif
 176
 177 #ifndef __HAVE_ARCH_STRNCAT
 178 /**
 179  * strncat - Append a length-limited, C-string to another
 180  * @dest: The string to be appended to
 181  * @src: The string to append to it
 182  * @count: The maximum numbers of bytes to copy
 183  *
 184  * Note that in contrast to strncpy(), strncat() ensures the result is
 185  * terminated.
 186  */
 187 char *strncat(char *dest, const char *src, size_t count)
 188 {
 189         char *tmp = dest;
 190
 191         if (count) {
 192                 while (*dest)
 193                         dest++;
 194                 while ((*dest++ = *src++) != 0) {
 195                         if (--count == 0) {
 196                                 *dest = '\0';
 197                                 break;
 198                         }
 199                 }
 200         }
 201         return tmp;
 202 }
 203 EXPORT_SYMBOL(strncat);
 204 #endif
 205
 206 #ifndef __HAVE_ARCH_STRLCAT
 207 /**
 208  * strlcat - Append a length-limited, C-string to another
 209  * @dest: The string to be appended to
 210  * @src: The string to append to it
 211  * @count: The size of the destination buffer.
 212  */
 213 size_t strlcat(char *dest, const char *src, size_t count)
 214 {
 215         size_t dsize = strlen(dest);
 216         size_t len = strlen(src);
 217         size_t res = dsize + len;
 218
 219         /* This would be a bug */
 220         BUG_ON(dsize >= count);
 221
 222         dest += dsize;
 223         count -= dsize;
 224         if (len >= count)
 225                 len = count-1;
 226         memcpy(dest, src, len);
 227         dest[len] = 0;
 228         return res;
 229 }
 230 EXPORT_SYMBOL(strlcat);
 231 #endif
 232
 233 #ifndef __HAVE_ARCH_STRCMP
 234 /**
 235  * strcmp - Compare two strings
 236  * @cs: One string
 237  * @ct: Another string
 238  */
 239 #undef strcmp
 240 int strcmp(const char *cs, const char *ct)
 241 {
 242         unsigned char c1, c2;
 243
 244         while (1) {
 245                 c1 = *cs++;
 246                 c2 = *ct++;
 247                 if (c1 != c2)
 248                         return c1 < c2 ? -1 : 1;
 249                 if (!c1)
 250                         break;
 251         }
 252         return 0;
 253 }
 254 EXPORT_SYMBOL(strcmp);
 255 #endif
 256
 257 #ifndef __HAVE_ARCH_STRNCMP
 258 /**
 259  * strncmp - Compare two length-limited strings
 260  * @cs: One string
 261  * @ct: Another string
 262  * @count: The maximum number of bytes to compare
 263  */
 264 int strncmp(const char *cs, const char *ct, size_t count)
 265 {
 266         unsigned char c1, c2;
 267
 268         while (count) {
 269                 c1 = *cs++;
 270                 c2 = *ct++;
 271                 if (c1 != c2)
 272                         return c1 < c2 ? -1 : 1;
 273                 if (!c1)
 274                         break;
 275                 count--;
 276         }
 277         return 0;
 278 }
 279 EXPORT_SYMBOL(strncmp);
 280 #endif
 281
 282 #ifndef __HAVE_ARCH_STRCHR
 283 /**
 284  * strchr - Find the first occurrence of a character in a string
 285  * @s: The string to be searched
 286  * @c: The character to search for
 287  */
 288 char *strchr(const char *s, int c)
 289 {
 290         for (; *s != (char)c; ++s)
 291                 if (*s == '\0')
 292                         return NULL;
 293         return (char *)s;
 294 }
 295 EXPORT_SYMBOL(strchr);
 296 #endif
 297
 298 #ifndef __HAVE_ARCH_STRCHRNUL
 299 /**
 300  * strchrnul - Find and return a character in a string, or end of string
 301  * @s: The string to be searched
 302  * @c: The character to search for
 303  *
 304  * Returns pointer to first occurrence of 'c' in s. If c is not found, then
 305  * return a pointer to the null byte at the end of s.
 306  */
 307 char *strchrnul(const char *s, int c)
 308 {
 309         while (*s && *s != (char)c)
 310                 s++;
 311         return (char *)s;
 312 }
 313 EXPORT_SYMBOL(strchrnul);
 314 #endif
 315
 316 #ifndef __HAVE_ARCH_STRRCHR
 317 /**
 318  * strrchr - Find the last occurrence of a character in a string
 319  * @s: The string to be searched
 320  * @c: The character to search for
 321  */
 322 char *strrchr(const char *s, int c)
 323 {
 324        const char *p = s + strlen(s);
 325        do {
 326            if (*p == (char)c)
 327                return (char *)p;
 328        } while (--p >= s);
 329        return NULL;
 330 }
 331 EXPORT_SYMBOL(strrchr);
 332 #endif
 333
 334 #ifndef __HAVE_ARCH_STRNCHR
 335 /**
 336  * strnchr - Find a character in a length limited string
 337  * @s: The string to be searched
 338  * @count: The number of characters to be searched
 339  * @c: The character to search for
 340  */
 341 char *strnchr(const char *s, size_t count, int c)
 342 {
 343         for (; count-- && *s != '\0'; ++s)
 344                 if (*s == (char)c)
 345                         return (char *)s;
 346         return NULL;
 347 }
 348 EXPORT_SYMBOL(strnchr);
 349 #endif
 350
 351 /**
 352  * skip_spaces - Removes leading whitespace from @str.
 353  * @str: The string to be stripped.
 354  *
 355  * Returns a pointer to the first non-whitespace character in @str.
 356  */
 357 char *skip_spaces(const char *str)
 358 {
 359         while (isspace(*str))
 360                 ++str;
 361         return (char *)str;
 362 }
 363 EXPORT_SYMBOL(skip_spaces);
 364
 365 /**
 366  * strim - Removes leading and trailing whitespace from @s.
 367  * @s: The string to be stripped.
 368  *
 369  * Note that the first trailing whitespace is replaced with a %NUL-terminator
 370  * in the given string @s. Returns a pointer to the first non-whitespace
 371  * character in @s.
 372  */
 373 char *strim(char *s)
 374 {
 375         size_t size;
 376         char *end;
 377
 378         size = strlen(s);
 379         if (!size)
 380                 return s;
 381
 382         end = s + size - 1;
 383         while (end >= s && isspace(*end))
 384                 end--;
 385         *(end + 1) = '\0';
 386
 387         return skip_spaces(s);
 388 }
 389 EXPORT_SYMBOL(strim);
 390
 391 #ifndef __HAVE_ARCH_STRLEN
 392 /**
 393  * strlen - Find the length of a string
 394  * @s: The string to be sized
 395  */
 396 size_t strlen(const char *s)
 397 {
 398         const char *sc;
 399
 400         for (sc = s; *sc != '\0'; ++sc)
 401                 /* nothing */;
 402         return sc - s;
 403 }
 404 EXPORT_SYMBOL(strlen);
 405 #endif
 406
 407 #ifndef __HAVE_ARCH_STRNLEN
 408 /**
 409  * strnlen - Find the length of a length-limited string
 410  * @s: The string to be sized
 411  * @count: The maximum number of bytes to search
 412  */
 413 size_t strnlen(const char *s, size_t count)
 414 {
 415         const char *sc;
 416
 417         for (sc = s; count-- && *sc != '\0'; ++sc)
 418                 /* nothing */;
 419         return sc - s;
 420 }
 421 EXPORT_SYMBOL(strnlen);
 422 #endif
 423
 424 #ifndef __HAVE_ARCH_STRSPN
 425 /**
 426  * strspn - Calculate the length of the initial substring of @s which only contain letters in @accept
 427  * @s: The string to be searched
 428  * @accept: The string to search for
 429  */
 430 size_t strspn(const char *s, const char *accept)
 431 {
 432         const char *p;
 433         const char *a;
 434         size_t count = 0;
 435
 436         for (p = s; *p != '\0'; ++p) {
 437                 for (a = accept; *a != '\0'; ++a) {
 438                         if (*p == *a)
 439                                 break;
 440                 }
 441                 if (*a == '\0')
 442                         return count;
 443                 ++count;
 444         }
 445         return count;
 446 }
 447
 448 EXPORT_SYMBOL(strspn);
 449 #endif
 450
 451 #ifndef __HAVE_ARCH_STRCSPN
 452 /**
 453  * strcspn - Calculate the length of the initial substring of @s which does not contain letters in @reject
 454  * @s: The string to be searched
 455  * @reject: The string to avoid
 456  */
 457 size_t strcspn(const char *s, const char *reject)
 458 {
 459         const char *p;
 460         const char *r;
 461         size_t count = 0;
 462
 463         for (p = s; *p != '\0'; ++p) {
 464                 for (r = reject; *r != '\0'; ++r) {
 465                         if (*p == *r)
 466                                 return count;
 467                 }
 468                 ++count;
 469         }
 470         return count;
 471 }
 472 EXPORT_SYMBOL(strcspn);
 473 #endif
 474
 475 #ifndef __HAVE_ARCH_STRPBRK
 476 /**
 477  * strpbrk - Find the first occurrence of a set of characters
 478  * @cs: The string to be searched
 479  * @ct: The characters to search for
 480  */
 481 char *strpbrk(const char *cs, const char *ct)
 482 {
 483         const char *sc1, *sc2;
 484
 485         for (sc1 = cs; *sc1 != '\0'; ++sc1) {
 486                 for (sc2 = ct; *sc2 != '\0'; ++sc2) {
 487                         if (*sc1 == *sc2)
 488                                 return (char *)sc1;
 489                 }
 490         }
 491         return NULL;
 492 }
 493 EXPORT_SYMBOL(strpbrk);
 494 #endif
 495
 496 #ifndef __HAVE_ARCH_STRSEP
 497 /**
 498  * strsep - Split a string into tokens
 499  * @s: The string to be searched
 500  * @ct: The characters to search for
 501  *
 502  * strsep() updates @s to point after the token, ready for the next call.
 503  *
 504  * It returns empty tokens, too, behaving exactly like the libc function
 505  * of that name. In fact, it was stolen from glibc2 and de-fancy-fied.
 506  * Same semantics, slimmer shape. ;)
 507  */
 508 char *strsep(char **s, const char *ct)
 509 {
 510         char *sbegin = *s;
 511         char *end;
 512
 513         if (sbegin == NULL)
 514                 return NULL;
 515
 516         end = strpbrk(sbegin, ct);
 517         if (end)
 518                 *end++ = '\0';
 519         *s = end;
 520         return sbegin;
 521 }
 522 EXPORT_SYMBOL(strsep);
 523 #endif
 524
 525 /**
 526  * sysfs_streq - return true if strings are equal, modulo trailing newline
 527  * @s1: one string
 528  * @s2: another string
 529  *
 530  * This routine returns true iff two strings are equal, treating both
 531  * NUL and newline-then-NUL as equivalent string terminations.  It's
 532  * geared for use with sysfs input strings, which generally terminate
 533  * with newlines but are compared against values without newlines.
 534  */
 535 bool sysfs_streq(const char *s1, const char *s2)
 536 {
 537         while (*s1 && *s1 == *s2) {
 538                 s1++;
 539                 s2++;
 540         }
 541
 542         if (*s1 == *s2)
 543                 return true;
 544         if (!*s1 && *s2 == '\n' && !s2[1])
 545                 return true;
 546         if (*s1 == '\n' && !s1[1] && !*s2)
 547                 return true;
 548         return false;
 549 }
 550 EXPORT_SYMBOL(sysfs_streq);
 551
 552 /**
 553  * strtobool - convert common user inputs into boolean values
 554  * @s: input string
 555  * @res: result
 556  *
 557  * This routine returns 0 iff the first character is one of 'Yy1Nn0'.
 558  * Otherwise it will return -EINVAL.  Value pointed to by res is
 559  * updated upon finding a match.
 560  */
 561 int strtobool(const char *s, bool *res)
 562 {
 563         switch (s[0]) {
 564         case 'y':
 565         case 'Y':
 566         case '1':
 567                 *res = true;
 568                 break;
 569         case 'n':
 570         case 'N':
 571         case '0':
 572                 *res = false;
 573                 break;
 574         default:
 575                 return -EINVAL;
 576         }
 577         return 0;
 578 }
 579 EXPORT_SYMBOL(strtobool);
 580
 581 #ifndef __HAVE_ARCH_MEMSET
 582 /**
 583  * memset - Fill a region of memory with the given value
 584  * @s: Pointer to the start of the area.
 585  * @c: The byte to fill the area with
 586  * @count: The size of the area.
 587  *
 588  * Do not use memset() to access IO space, use memset_io() instead.
 589  */
 590 void *memset(void *s, int c, size_t count)
 591 {
 592         char *xs = s;
 593
 594         while (count--)
 595                 *xs++ = c;
 596         return s;
 597 }
 598 EXPORT_SYMBOL(memset);
 599 #endif
 600
 601 /**
 602  * memzero_explicit - Fill a region of memory (e.g. sensitive
 603  *                    keying data) with 0s.
 604  * @s: Pointer to the start of the area.
 605  * @count: The size of the area.
 606  *
 607  * memzero_explicit() doesn't need an arch-specific version as
 608  * it just invokes the one of memset() implicitly.
 609  */
 610 void memzero_explicit(void *s, size_t count)
 611 {
 612         memset(s, 0, count);
 613         OPTIMIZER_HIDE_VAR(s);
 614 }
 615 EXPORT_SYMBOL(memzero_explicit);
 616
 617 #ifndef __HAVE_ARCH_MEMCPY
 618 /**
 619  * memcpy - Copy one area of memory to another
 620  * @dest: Where to copy to
 621  * @src: Where to copy from
 622  * @count: The size of the area.
 623  *
 624  * You should not use this function to access IO space, use memcpy_toio()
 625  * or memcpy_fromio() instead.
 626  */
 627 void *memcpy(void *dest, const void *src, size_t count)
 628 {
 629         char *tmp = dest;
 630         const char *s = src;
 631
 632         while (count--)
 633                 *tmp++ = *s++;
 634         return dest;
 635 }
 636 EXPORT_SYMBOL(memcpy);
 637 #endif
 638
 639 #ifndef __HAVE_ARCH_MEMMOVE
 640 /**
 641  * memmove - Copy one area of memory to another
 642  * @dest: Where to copy to
 643  * @src: Where to copy from
 644  * @count: The size of the area.
 645  *
 646  * Unlike memcpy(), memmove() copes with overlapping areas.
 647  */
 648 void *memmove(void *dest, const void *src, size_t count)
 649 {
 650         char *tmp;
 651         const char *s;
 652
 653         if (dest <= src) {
 654                 tmp = dest;
 655                 s = src;
 656                 while (count--)
 657                         *tmp++ = *s++;
 658         } else {
 659                 tmp = dest;
 660                 tmp += count;
 661                 s = src;
 662                 s += count;
 663                 while (count--)
 664                         *--tmp = *--s;
 665         }
 666         return dest;
 667 }
 668 EXPORT_SYMBOL(memmove);
 669 #endif
 670
 671 #ifndef __HAVE_ARCH_MEMCMP
 672 /**
 673  * memcmp - Compare two areas of memory
 674  * @cs: One area of memory
 675  * @ct: Another area of memory
 676  * @count: The size of the area.
 677  */
 678 #undef memcmp
 679 __visible int memcmp(const void *cs, const void *ct, size_t count)
 680 {
 681         const unsigned char *su1, *su2;
 682         int res = 0;
 683
 684         for (su1 = cs, su2 = ct; 0 < count; ++su1, ++su2, count--)
 685                 if ((res = *su1 - *su2) != 0)
 686                         break;
 687         return res;
 688 }
 689 EXPORT_SYMBOL(memcmp);
 690 #endif
 691
 692 #ifndef __HAVE_ARCH_MEMSCAN
 693 /**
 694  * memscan - Find a character in an area of memory.
 695  * @addr: The memory area
 696  * @c: The byte to search for
 697  * @size: The size of the area.
 698  *
 699  * returns the address of the first occurrence of @c, or 1 byte past
 700  * the area if @c is not found
 701  */
 702 void *memscan(void *addr, int c, size_t size)
 703 {
 704         unsigned char *p = addr;
 705
 706         while (size) {
 707                 if (*p == c)
 708                         return (void *)p;
 709                 p++;
 710                 size--;
 711         }
 712         return (void *)p;
 713 }
 714 EXPORT_SYMBOL(memscan);
 715 #endif
 716
 717 #ifndef __HAVE_ARCH_STRSTR
 718 /**
 719  * strstr - Find the first substring in a %NUL terminated string
 720  * @s1: The string to be searched
 721  * @s2: The string to search for
 722  */
 723 char *strstr(const char *s1, const char *s2)
 724 {
 725         size_t l1, l2;
 726
 727         l2 = strlen(s2);
 728         if (!l2)
 729                 return (char *)s1;
 730         l1 = strlen(s1);
 731         while (l1 >= l2) {
 732                 l1--;
 733                 if (!memcmp(s1, s2, l2))
 734                         return (char *)s1;
 735                 s1++;
 736         }
 737         return NULL;
 738 }
 739 EXPORT_SYMBOL(strstr);
 740 #endif
 741
 742 #ifndef __HAVE_ARCH_STRNSTR
 743 /**
 744  * strnstr - Find the first substring in a length-limited string
 745  * @s1: The string to be searched
 746  * @s2: The string to search for
 747  * @len: the maximum number of characters to search
 748  */
 749 char *strnstr(const char *s1, const char *s2, size_t len)
 750 {
 751         size_t l2;
 752
 753         l2 = strlen(s2);
 754         if (!l2)
 755                 return (char *)s1;
 756         while (len >= l2) {
 757                 len--;
 758                 if (!memcmp(s1, s2, l2))
 759                         return (char *)s1;
 760                 s1++;
 761         }
 762         return NULL;
 763 }
 764 EXPORT_SYMBOL(strnstr);
 765 #endif
 766
 767 #ifndef __HAVE_ARCH_MEMCHR
 768 /**
 769  * memchr - Find a character in an area of memory.
 770  * @s: The memory area
 771  * @c: The byte to search for
 772  * @n: The size of the area.
 773  *
 774  * returns the address of the first occurrence of @c, or %NULL
 775  * if @c is not found
 776  */
 777 void *memchr(const void *s, int c, size_t n)
 778 {
 779         const unsigned char *p = s;
 780         while (n-- != 0) {
 781                 if ((unsigned char)c == *p++) {
 782                         return (void *)(p - 1);
 783                 }
 784         }
 785         return NULL;
 786 }
 787 EXPORT_SYMBOL(memchr);
 788 #endif
 789
 790 static void *check_bytes8(const u8 *start, u8 value, unsigned int bytes)
 791 {
 792         while (bytes) {
 793                 if (*start != value)
 794                         return (void *)start;
 795                 start++;
 796                 bytes--;
 797         }
 798         return NULL;
 799 }
 800
 801 /**
 802  * memchr_inv - Find an unmatching character in an area of memory.
 803  * @start: The memory area
 804  * @c: Find a character other than c
 805  * @bytes: The size of the area.
 806  *
 807  * returns the address of the first character other than @c, or %NULL
 808  * if the whole buffer contains just @c.
 809  */
 810 void *memchr_inv(const void *start, int c, size_t bytes)
 811 {
 812         u8 value = c;
 813         u64 value64;
 814         unsigned int words, prefix;
 815
 816         if (bytes <= 16)
 817                 return check_bytes8(start, value, bytes);
 818
 819         value64 = value;
 820 #if defined(CONFIG_ARCH_HAS_FAST_MULTIPLIER) && BITS_PER_LONG == 64
 821         value64 *= 0x0101010101010101;
 822 #elif defined(CONFIG_ARCH_HAS_FAST_MULTIPLIER)
 823         value64 *= 0x01010101;
 824         value64 |= value64 << 32;
 825 #else
 826         value64 |= value64 << 8;
 827         value64 |= value64 << 16;
 828         value64 |= value64 << 32;
 829 #endif
 830
 831         prefix = (unsigned long)start % 8;
 832         if (prefix) {
 833                 u8 *r;
 834
 835                 prefix = 8 - prefix;
 836                 r = check_bytes8(start, value, prefix);
 837                 if (r)
 838                         return r;
 839                 start += prefix;
 840                 bytes -= prefix;
 841         }
 842
 843         words = bytes / 8;
 844
 845         while (words) {
 846                 if (*(u64 *)start != value64)
 847                         return check_bytes8(start, value, 8);
 848                 start += 8;
 849                 words--;
 850         }
 851
 852         return check_bytes8(start, value, bytes % 8);
 853 }
 854 EXPORT_SYMBOL(memchr_inv);