138 lines
3.7 KiB
C
138 lines
3.7 KiB
C
/*
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FUNCTION
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<<memccpy>>---copy memory regions with end-token check
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SYNOPSIS
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#include <string.h>
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void* memccpy(void *restrict <[out]>, const void *restrict <[in]>,
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int <[endchar]>, size_t <[n]>);
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DESCRIPTION
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This function copies up to <[n]> bytes from the memory region
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pointed to by <[in]> to the memory region pointed to by
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<[out]>. If a byte matching the <[endchar]> is encountered,
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the byte is copied and copying stops.
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If the regions overlap, the behavior is undefined.
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RETURNS
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<<memccpy>> returns a pointer to the first byte following the
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<[endchar]> in the <[out]> region. If no byte matching
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<[endchar]> was copied, then <<NULL>> is returned.
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PORTABILITY
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<<memccpy>> is a GNU extension.
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<<memccpy>> requires no supporting OS subroutines.
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*/
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#include <_ansi.h>
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#include <stddef.h>
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#include <string.h>
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#include <limits.h>
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/* Nonzero if either X or Y is not aligned on a "long" boundary. */
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#define UNALIGNED(X, Y) \
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(((long)X & (sizeof (long) - 1)) | ((long)Y & (sizeof (long) - 1)))
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/* How many bytes are copied each iteration of the word copy loop. */
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#define LITTLEBLOCKSIZE (sizeof (long))
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/* Threshhold for punting to the byte copier. */
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#define TOO_SMALL(LEN) ((LEN) < LITTLEBLOCKSIZE)
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/* Macros for detecting endchar */
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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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_PTR
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_DEFUN (memccpy, (dst0, src0, endchar, len0),
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_PTR __restrict dst0 _AND
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_CONST _PTR __restrict src0 _AND
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int endchar0 _AND
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size_t len0)
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{
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#if defined(PREFER_SIZE_OVER_SPEED) || defined(__OPTIMIZE_SIZE__)
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_PTR ptr = NULL;
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char *dst = (char *) dst0;
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char *src = (char *) src0;
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char endchar = endchar0 & 0xff;
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while (len0--)
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{
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if ((*dst++ = *src++) == endchar)
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{
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ptr = dst;
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break;
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}
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}
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return ptr;
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#else
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_PTR ptr = NULL;
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char *dst = dst0;
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_CONST char *src = src0;
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long *aligned_dst;
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_CONST long *aligned_src;
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char endchar = endchar0 & 0xff;
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/* If the size is small, or either SRC or DST is unaligned,
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then punt into the byte copy loop. This should be rare. */
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if (!TOO_SMALL(len0) && !UNALIGNED (src, dst))
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{
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unsigned int i;
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unsigned long mask = 0;
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aligned_dst = (long*)dst;
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aligned_src = (long*)src;
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/* The fast code reads the ASCII 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 NULL in the
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result. */
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for (i = 0; i < LITTLEBLOCKSIZE; i++)
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mask = (mask << 8) + endchar;
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/* Copy one long word at a time if possible. */
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while (len0 >= LITTLEBLOCKSIZE)
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{
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unsigned long buffer = (unsigned long)(*aligned_src);
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buffer ^= mask;
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if (DETECTNULL (buffer))
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break; /* endchar is found, go byte by byte from here */
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*aligned_dst++ = *aligned_src++;
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len0 -= LITTLEBLOCKSIZE;
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}
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/* Pick up any residual with a byte copier. */
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dst = (char*)aligned_dst;
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src = (char*)aligned_src;
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}
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while (len0--)
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{
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if ((*dst++ = *src++) == endchar)
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{
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ptr = dst;
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break;
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}
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}
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return ptr;
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#endif /* not PREFER_SIZE_OVER_SPEED */
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}
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