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