111 lines
2.7 KiB
C
111 lines
2.7 KiB
C
/*
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FUNCTION
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<<memcpy>>---copy memory regions
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ANSI_SYNOPSIS
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#include <string.h>
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void* memcpy(void *<[out]>, const void *<[in]>, size_t <[n]>);
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TRAD_SYNOPSIS
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#include <string.h>
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void *memcpy(<[out]>, <[in]>, <[n]>
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void *<[out]>;
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void *<[in]>;
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size_t <[n]>;
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DESCRIPTION
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This function copies <[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]>.
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If the regions overlap, the behavior is undefined.
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RETURNS
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<<memcpy>> returns a pointer to the first byte of the <[out]>
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region.
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PORTABILITY
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<<memcpy>> is ANSI C.
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<<memcpy>> requires no supporting OS subroutines.
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QUICKREF
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memcpy ansi pure
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*/
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#include <_ansi.h>
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#include <string.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 4X unrolled loop. */
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#define BIGBLOCKSIZE (sizeof (long) << 2)
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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) < BIGBLOCKSIZE)
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_PTR
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_DEFUN (memcpy, (dst0, src0, len0),
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_PTR dst0 _AND
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_CONST _PTR src0 _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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char *dst = (char *) dst0;
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char *src = (char *) src0;
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_PTR save = dst0;
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while (len0--)
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{
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*dst++ = *src++;
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}
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return save;
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#else
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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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/* 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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aligned_dst = (long*)dst;
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aligned_src = (long*)src;
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/* Copy 4X long words at a time if possible. */
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while (len0 >= BIGBLOCKSIZE)
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{
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*aligned_dst++ = *aligned_src++;
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*aligned_dst++ = *aligned_src++;
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*aligned_dst++ = *aligned_src++;
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*aligned_dst++ = *aligned_src++;
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len0 -= BIGBLOCKSIZE;
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}
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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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*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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*dst++ = *src++;
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return dst0;
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#endif /* not PREFER_SIZE_OVER_SPEED */
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}
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