117 lines
2.7 KiB
C
117 lines
2.7 KiB
C
/*
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FUNCTION
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<<strchr>>---search for character in string
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INDEX
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strchr
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SYNOPSIS
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#include <string.h>
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char * strchr(const char *<[string]>, int <[c]>);
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DESCRIPTION
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This function finds the first occurence of <[c]> (converted to
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a char) in the string pointed to by <[string]> (including the
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terminating null character).
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RETURNS
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Returns a pointer to the located character, or a null pointer
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if <[c]> does not occur in <[string]>.
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PORTABILITY
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<<strchr>> is ANSI C.
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<<strchr>> requires no supporting OS subroutines.
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QUICKREF
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strchr ansi pure
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*/
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#include <string.h>
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#include <limits.h>
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/* Nonzero if X is not aligned on a "long" boundary. */
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#define UNALIGNED(X) ((long)X & (sizeof (long) - 1))
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/* How many bytes are loaded each iteration of the word copy loop. */
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#define LBLOCKSIZE (sizeof (long))
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#if LONG_MAX == 2147483647L
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#define DETECTNULL(X) (((X) - 0x01010101) & ~(X) & 0x80808080)
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#else
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#if LONG_MAX == 9223372036854775807L
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/* Nonzero if X (a long int) contains a NULL byte. */
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#define DETECTNULL(X) (((X) - 0x0101010101010101) & ~(X) & 0x8080808080808080)
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#else
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#error long int is not a 32bit or 64bit type.
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#endif
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#endif
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/* DETECTCHAR returns nonzero if (long)X contains the byte used
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to fill (long)MASK. */
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#define DETECTCHAR(X,MASK) (DETECTNULL(X ^ MASK))
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char *
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strchr (const char *s1,
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int i)
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{
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const unsigned char *s = (const unsigned char *)s1;
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unsigned char c = i;
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#if !defined(PREFER_SIZE_OVER_SPEED) && !defined(__OPTIMIZE_SIZE__)
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unsigned long mask,j;
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unsigned long *aligned_addr;
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/* Special case for finding 0. */
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if (!c)
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{
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while (UNALIGNED (s))
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{
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if (!*s)
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return (char *) s;
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s++;
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}
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/* Operate a word at a time. */
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aligned_addr = (unsigned long *) s;
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while (!DETECTNULL (*aligned_addr))
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aligned_addr++;
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/* Found the end of string. */
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s = (const unsigned char *) aligned_addr;
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while (*s)
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s++;
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return (char *) s;
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}
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/* All other bytes. Align the pointer, then search a long at a time. */
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while (UNALIGNED (s))
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{
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if (!*s)
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return NULL;
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if (*s == c)
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return (char *) s;
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s++;
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}
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mask = c;
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for (j = 8; j < LBLOCKSIZE * 8; j <<= 1)
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mask = (mask << j) | mask;
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aligned_addr = (unsigned long *) s;
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while (!DETECTNULL (*aligned_addr) && !DETECTCHAR (*aligned_addr, mask))
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aligned_addr++;
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/* The block of bytes currently pointed to by aligned_addr
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contains either a null or the target char, or both. We
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catch it using the bytewise search. */
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s = (unsigned char *) aligned_addr;
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#endif /* not PREFER_SIZE_OVER_SPEED */
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while (*s && *s != c)
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s++;
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if (*s == c)
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return (char *)s;
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return NULL;
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}
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