116 lines
2.8 KiB
C
116 lines
2.8 KiB
C
/*
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FUNCTION
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<<rawmemchr>>---find character in memory
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INDEX
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rawmemchr
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SYNOPSIS
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#include <string.h>
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void *rawmemchr(const void *<[src]>, int <[c]>);
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DESCRIPTION
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This function searches memory starting at <<*<[src]>>> for the
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character <[c]>. The search only ends with the first occurrence
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of <[c]>; in particular, <<NUL>> does not terminate the search.
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No bounds checking is performed, so this function should only
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be used when it is certain that the character <[c]> will be found.
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RETURNS
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A pointer to the first occurance of character <[c]>.
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PORTABILITY
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<<rawmemchr>> is a GNU extension.
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<<rawmemchr>> requires no supporting OS subroutines.
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QUICKREF
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rawmemchr
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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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/* 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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/* Threshhold for punting to the bytewise iterator. */
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#define TOO_SMALL(LEN) ((LEN) < LBLOCKSIZE)
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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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/* 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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void *
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_DEFUN (rawmemchr, (src_void, c),
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const void *src_void,
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int c)
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{
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const unsigned char *src = (const unsigned char *) src_void;
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unsigned char d = c;
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#if !defined(PREFER_SIZE_OVER_SPEED) && !defined(__OPTIMIZE_SIZE__)
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unsigned long *asrc;
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unsigned long mask;
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unsigned int i;
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while (UNALIGNED (src))
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{
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if (*src == d)
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return (void *) src;
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src++;
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}
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/* If we get this far, we know that src is word-aligned. */
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/* The fast code reads the source one word at a time and only
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performs the bytewise search on word-sized segments if they
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contain the search character, which is detected by XORing
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the word-sized segment with a word-sized block of the search
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character and then detecting for the presence of NUL in the
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result. */
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asrc = (unsigned long *) src;
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mask = d << 8 | d;
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mask = mask << 16 | mask;
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for (i = 32; i < LBLOCKSIZE * 8; i <<= 1)
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mask = (mask << i) | mask;
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while (1)
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{
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if (DETECTCHAR (*asrc, mask))
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break;
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asrc++;
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}
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/* We have the matching word, now we resort to a bytewise loop. */
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src = (unsigned char *) asrc;
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#endif /* !PREFER_SIZE_OVER_SPEED && !__OPTIMIZE_SIZE__ */
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while (1)
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{
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if (*src == d)
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return (void *) src;
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src++;
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}
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}
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