newlib/libc/string/strchr.c

   1 /*
   2 FUNCTION
   3         <<strchr>>---search for character in string
   4
   5 INDEX
   6         strchr
   7
   8 SYNOPSIS
   9         #include <string.h>
  10         char * strchr(const char *<[string]>, int <[c]>);
  11
  12 DESCRIPTION
  13         This function finds the first occurence of <[c]> (converted to
  14         a char) in the string pointed to by <[string]> (including the
  15         terminating null character).
  16
  17 RETURNS
  18         Returns a pointer to the located character, or a null pointer
  19         if <[c]> does not occur in <[string]>.
  20
  21 PORTABILITY
  22 <<strchr>> is ANSI C.
  23
  24 <<strchr>> requires no supporting OS subroutines.
  25
  26 QUICKREF
  27         strchr ansi pure
  28 */
  29
  30 #include <string.h>
  31 #include <limits.h>
  32
  33 /* Nonzero if X is not aligned on a "long" boundary.  */
  34 #define UNALIGNED(X) ((long)X & (sizeof (long) - 1))
  35
  36 /* How many bytes are loaded each iteration of the word copy loop.  */
  37 #define LBLOCKSIZE (sizeof (long))
  38
  39 #if LONG_MAX == 2147483647L
  40 #define DETECTNULL(X) (((X) - 0x01010101) & ~(X) & 0x80808080)
  41 #else
  42 #if LONG_MAX == 9223372036854775807L
  43 /* Nonzero if X (a long int) contains a NULL byte. */
  44 #define DETECTNULL(X) (((X) - 0x0101010101010101) & ~(X) & 0x8080808080808080)
  45 #else
  46 #error long int is not a 32bit or 64bit type.
  47 #endif
  48 #endif
  49
  50 /* DETECTCHAR returns nonzero if (long)X contains the byte used
  51    to fill (long)MASK. */
  52 #define DETECTCHAR(X,MASK) (DETECTNULL(X ^ MASK))
  53
  54 char *
  55 strchr (const char *s1,
  56         int i)
  57 {
  58   const unsigned char *s = (const unsigned char *)s1;
  59   unsigned char c = i;
  60
  61 #if !defined(PREFER_SIZE_OVER_SPEED) && !defined(__OPTIMIZE_SIZE__)
  62   unsigned long mask,j;
  63   unsigned long *aligned_addr;
  64
  65   /* Special case for finding 0.  */
  66   if (!c)
  67     {
  68       while (UNALIGNED (s))
  69         {
  70           if (!*s)
  71             return (char *) s;
  72           s++;
  73         }
  74       /* Operate a word at a time.  */
  75       aligned_addr = (unsigned long *) s;
  76       while (!DETECTNULL (*aligned_addr))
  77         aligned_addr++;
  78       /* Found the end of string.  */
  79       s = (const unsigned char *) aligned_addr;
  80       while (*s)
  81         s++;
  82       return (char *) s;
  83     }
  84
  85   /* All other bytes.  Align the pointer, then search a long at a time.  */
  86   while (UNALIGNED (s))
  87     {
  88       if (!*s)
  89         return NULL;
  90       if (*s == c)
  91         return (char *) s;
  92       s++;
  93     }
  94
  95   mask = c;
  96   for (j = 8; j < LBLOCKSIZE * 8; j <<= 1)
  97     mask = (mask << j) | mask;
  98
  99   aligned_addr = (unsigned long *) s;
 100   while (!DETECTNULL (*aligned_addr) && !DETECTCHAR (*aligned_addr, mask))
 101     aligned_addr++;
 102
 103   /* The block of bytes currently pointed to by aligned_addr
 104      contains either a null or the target char, or both.  We
 105      catch it using the bytewise search.  */
 106
 107   s = (unsigned char *) aligned_addr;
 108
 109 #endif /* not PREFER_SIZE_OVER_SPEED */
 110
 111   while (*s && *s != c)
 112     s++;
 113   if (*s == c)
 114     return (char *)s;
 115   return NULL;
 116 }