xref: /linux/arch/csky/lib/string.c (revision c532de5a67a70f8533d495f8f2aaa9a0491c3ad0)
1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * String functions optimized for hardware which doesn't
4  * handle unaligned memory accesses efficiently.
5  *
6  * Copyright (C) 2021 Matteo Croce
7  */
8 
9 #include <linux/types.h>
10 #include <linux/module.h>
11 
12 /* Minimum size for a word copy to be convenient */
13 #define BYTES_LONG	sizeof(long)
14 #define WORD_MASK	(BYTES_LONG - 1)
15 #define MIN_THRESHOLD	(BYTES_LONG * 2)
16 
17 /* convenience union to avoid cast between different pointer types */
18 union types {
19 	u8 *as_u8;
20 	unsigned long *as_ulong;
21 	uintptr_t as_uptr;
22 };
23 
24 union const_types {
25 	const u8 *as_u8;
26 	unsigned long *as_ulong;
27 	uintptr_t as_uptr;
28 };
29 
30 void *memcpy(void *dest, const void *src, size_t count)
31 {
32 	union const_types s = { .as_u8 = src };
33 	union types d = { .as_u8 = dest };
34 	int distance = 0;
35 
36 	if (count < MIN_THRESHOLD)
37 		goto copy_remainder;
38 
39 	/* Copy a byte at time until destination is aligned. */
40 	for (; d.as_uptr & WORD_MASK; count--)
41 		*d.as_u8++ = *s.as_u8++;
42 
43 	distance = s.as_uptr & WORD_MASK;
44 
45 	if (distance) {
46 		unsigned long last, next;
47 
48 		/*
49 		 * s is distance bytes ahead of d, and d just reached
50 		 * the alignment boundary. Move s backward to word align it
51 		 * and shift data to compensate for distance, in order to do
52 		 * word-by-word copy.
53 		 */
54 		s.as_u8 -= distance;
55 
56 		next = s.as_ulong[0];
57 		for (; count >= BYTES_LONG; count -= BYTES_LONG) {
58 			last = next;
59 			next = s.as_ulong[1];
60 
61 			d.as_ulong[0] = last >> (distance * 8) |
62 				next << ((BYTES_LONG - distance) * 8);
63 
64 			d.as_ulong++;
65 			s.as_ulong++;
66 		}
67 
68 		/* Restore s with the original offset. */
69 		s.as_u8 += distance;
70 	} else {
71 		/*
72 		 * If the source and dest lower bits are the same, do a simple
73 		 * 32/64 bit wide copy.
74 		 */
75 		for (; count >= BYTES_LONG; count -= BYTES_LONG)
76 			*d.as_ulong++ = *s.as_ulong++;
77 	}
78 
79 copy_remainder:
80 	while (count--)
81 		*d.as_u8++ = *s.as_u8++;
82 
83 	return dest;
84 }
85 EXPORT_SYMBOL(memcpy);
86 
87 /*
88  * Simply check if the buffer overlaps an call memcpy() in case,
89  * otherwise do a simple one byte at time backward copy.
90  */
91 void *memmove(void *dest, const void *src, size_t count)
92 {
93 	if (dest < src || src + count <= dest)
94 		return memcpy(dest, src, count);
95 
96 	if (dest > src) {
97 		const char *s = src + count;
98 		char *tmp = dest + count;
99 
100 		while (count--)
101 			*--tmp = *--s;
102 	}
103 	return dest;
104 }
105 EXPORT_SYMBOL(memmove);
106 
107 void *memset(void *s, int c, size_t count)
108 {
109 	union types dest = { .as_u8 = s };
110 
111 	if (count >= MIN_THRESHOLD) {
112 		unsigned long cu = (unsigned long)c;
113 
114 		/* Compose an ulong with 'c' repeated 4/8 times */
115 		cu |= cu << 8;
116 		cu |= cu << 16;
117 		/* Suppress warning on 32 bit machines */
118 		cu |= (cu << 16) << 16;
119 
120 		for (; count && dest.as_uptr & WORD_MASK; count--)
121 			*dest.as_u8++ = c;
122 
123 		/* Copy using the largest size allowed */
124 		for (; count >= BYTES_LONG; count -= BYTES_LONG)
125 			*dest.as_ulong++ = cu;
126 	}
127 
128 	/* copy the remainder */
129 	while (count--)
130 		*dest.as_u8++ = c;
131 
132 	return s;
133 }
134 EXPORT_SYMBOL(memset);
135