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memcpy.c revision 1.1.16.2 
      1 /* $NetBSD: memcpy.c,v 1.1.16.2 2020/04/21 19:37:45 martin Exp $ */
      2 /*-
      3  * Copyright (c) 2014 The NetBSD Foundation, Inc.
      4  * All rights reserved.
      5  *
      6  * This code is derived from software contributed to The NetBSD Foundation
      7  * by Matt Thomas of 3am Software Foundry.
      8  *
      9  * Redistribution and use in source and binary forms, with or without
     10  * modification, are permitted provided that the following conditions
     11  * are met:
     12  * 1. Redistributions of source code must retain the above copyright
     13  *    notice, this list of conditions and the following disclaimer.
     14  * 2. Redistributions in binary form must reproduce the above copyright
     15  *    notice, this list of conditions and the following disclaimer in the
     16  *    documentation and/or other materials provided with the distribution.
     17  *
     18  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
     19  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
     20  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
     21  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
     22  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
     23  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
     24  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
     25  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
     26  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     27  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
     28  * POSSIBILITY OF SUCH DAMAGE.
     29  */
     30 
     31 #include <sys/cdefs.h>
     32 
     33 __RCSID("$NetBSD: memcpy.c,v 1.1.16.2 2020/04/21 19:37:45 martin Exp $");
     34 
     35 #include <stddef.h>
     36 #include <stdint.h>
     37 #include <string.h>
     38 
     39 static inline unsigned long
     40 combine_words(unsigned long w1, unsigned long w2, int shift1, int shift2)
     41 {
     42 #if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
     43 	return (w1 << shift1) | (w2 >> shift2);
     44 #else
     45 	return (w1 >> shift1) | (w2 << shift2);
     46 #endif
     47 }
     48 
     49 void *
     50 memcpy(void * restrict a, const void * restrict b, size_t len)
     51 {
     52 	const unsigned char *cb = b;
     53 	unsigned char *ca = a;
     54 
     55 	if (len == 0)
     56 		return a;
     57 
     58 	/*
     59 	 * Make sure the destination is long aligned.
     60 	 */
     61 	while ((uintptr_t)ca & (sizeof(long) - 1)) {
     62 		*ca++ = *cb++;
     63 		if (--len == 0)
     64 			return a;
     65 	}
     66 
     67 	unsigned long *la = (long *)ca;
     68 	const int offset = (uintptr_t)cb & (sizeof(*la) - 1);
     69 	const unsigned long *lb = (const unsigned long *) (cb - offset);
     70 	unsigned long * const ea = la + len / sizeof(*la);
     71 
     72 	if (offset == 0) {
     73 		/*
     74 		 * a & b are now both long alignment.
     75 		 * First try to copy 4 longs at a time,
     76 		 */
     77 		for (; la + 4 <= ea; la += 4, lb += 4) {
     78 			la[0] = lb[0];
     79 			la[1] = lb[1];
     80 			la[2] = lb[2];
     81 			la[3] = lb[3];
     82 		}
     83 		/*
     84 		 * Now try to copy one long at a time.
     85 		 */
     86 		while (la <= ea) {
     87 			*la++ = *lb++;
     88 		}
     89 	} else {
     90 		const int shift1 = offset * 8;
     91 		const int shift2 = sizeof(*la) * 8 - shift1;
     92 		unsigned long w1 = *lb++;
     93 
     94 		/*
     95 		 * We try to write 4 words per loop.
     96 		 */
     97 		for (; la + 4 <= ea; la += 4, lb += 4) {
     98 			unsigned long w2 = lb[0];
     99 
    100 			la[0] = combine_words(w1, w2, shift1, shift2);
    101 
    102 			w1 = lb[1];
    103 
    104 			la[1] = combine_words(w2, w1, shift1, shift2);
    105 
    106 			w2 = lb[2];
    107 
    108 			la[2] = combine_words(w1, w2, shift1, shift2);
    109 
    110 			w1 = lb[3];
    111 
    112 			la[3] = combine_words(w2, w1, shift1, shift2);
    113 		}
    114 
    115 		/*
    116 		 * Now try to copy one long at a time.
    117 		 */
    118 		while (la <= ea) {
    119 			unsigned long w2 = *lb++;
    120 
    121 			*la++ = combine_words(w1, w2, shift1, shift2);
    122 
    123 			w1 = w2;
    124 		}
    125 	}
    126 	len &= sizeof(*la) - 1;
    127 	if (len) {
    128 		cb = (const unsigned char *)lb + offset;
    129 		ca = (unsigned char *)la;
    130 		while (len-- > 0) {
    131 			*ca++ = *cb++;
    132 		}
    133 	}
    134 	return a;
    135 }
    136