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89 lines
1.8 KiB
C
89 lines
1.8 KiB
C
/*
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FUNCTION
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<<strlen>>---character string length
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INDEX
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strlen
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ANSI_SYNOPSIS
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#include <string.h>
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size_t strlen(const char *<[str]>);
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TRAD_SYNOPSIS
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#include <string.h>
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size_t strlen(<[str]>)
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char *<[src]>;
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DESCRIPTION
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The <<strlen>> function works out the length of the string
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starting at <<*<[str]>>> by counting chararacters until it
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reaches a <<NULL>> character.
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RETURNS
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<<strlen>> returns the character count.
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PORTABILITY
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<<strlen>> is ANSI C.
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<<strlen>> requires no supporting OS subroutines.
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QUICKREF
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strlen ansi pure
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*/
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#include <_ansi.h>
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#include <string.h>
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#include <limits.h>
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#define LBLOCKSIZE (sizeof (long))
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#define UNALIGNED(X) ((long)X & (LBLOCKSIZE - 1))
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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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#ifndef DETECTNULL
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#error long int is not a 32bit or 64bit byte
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#endif
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size_t
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_DEFUN (strlen, (str),
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_CONST char *str)
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{
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_CONST char *start = str;
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#if !defined(PREFER_SIZE_OVER_SPEED) && !defined(__OPTIMIZE_SIZE__)
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unsigned long *aligned_addr;
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/* Align the pointer, so we can search a word at a time. */
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while (UNALIGNED (str))
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{
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if (!*str)
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return str - start;
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str++;
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}
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/* If the string is word-aligned, we can check for the presence of
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a null in each word-sized block. */
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aligned_addr = (unsigned long *)str;
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while (!DETECTNULL (*aligned_addr))
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aligned_addr++;
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/* Once a null is detected, we check each byte in that block for a
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precise position of the null. */
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str = (char *) aligned_addr;
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#endif /* not PREFER_SIZE_OVER_SPEED */
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while (*str)
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str++;
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return str - start;
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}
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