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Diffstat (limited to '')
-rw-r--r-- | arch/csky/lib/string.c | 134 |
1 files changed, 134 insertions, 0 deletions
diff --git a/arch/csky/lib/string.c b/arch/csky/lib/string.c new file mode 100644 index 000000000..d65626fca --- /dev/null +++ b/arch/csky/lib/string.c @@ -0,0 +1,134 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * String functions optimized for hardware which doesn't + * handle unaligned memory accesses efficiently. + * + * Copyright (C) 2021 Matteo Croce + */ + +#include <linux/types.h> +#include <linux/module.h> + +/* Minimum size for a word copy to be convenient */ +#define BYTES_LONG sizeof(long) +#define WORD_MASK (BYTES_LONG - 1) +#define MIN_THRESHOLD (BYTES_LONG * 2) + +/* convenience union to avoid cast between different pointer types */ +union types { + u8 *as_u8; + unsigned long *as_ulong; + uintptr_t as_uptr; +}; + +union const_types { + const u8 *as_u8; + unsigned long *as_ulong; + uintptr_t as_uptr; +}; + +void *memcpy(void *dest, const void *src, size_t count) +{ + union const_types s = { .as_u8 = src }; + union types d = { .as_u8 = dest }; + int distance = 0; + + if (count < MIN_THRESHOLD) + goto copy_remainder; + + /* Copy a byte at time until destination is aligned. */ + for (; d.as_uptr & WORD_MASK; count--) + *d.as_u8++ = *s.as_u8++; + + distance = s.as_uptr & WORD_MASK; + + if (distance) { + unsigned long last, next; + + /* + * s is distance bytes ahead of d, and d just reached + * the alignment boundary. Move s backward to word align it + * and shift data to compensate for distance, in order to do + * word-by-word copy. + */ + s.as_u8 -= distance; + + next = s.as_ulong[0]; + for (; count >= BYTES_LONG; count -= BYTES_LONG) { + last = next; + next = s.as_ulong[1]; + + d.as_ulong[0] = last >> (distance * 8) | + next << ((BYTES_LONG - distance) * 8); + + d.as_ulong++; + s.as_ulong++; + } + + /* Restore s with the original offset. */ + s.as_u8 += distance; + } else { + /* + * If the source and dest lower bits are the same, do a simple + * 32/64 bit wide copy. + */ + for (; count >= BYTES_LONG; count -= BYTES_LONG) + *d.as_ulong++ = *s.as_ulong++; + } + +copy_remainder: + while (count--) + *d.as_u8++ = *s.as_u8++; + + return dest; +} +EXPORT_SYMBOL(memcpy); + +/* + * Simply check if the buffer overlaps an call memcpy() in case, + * otherwise do a simple one byte at time backward copy. + */ +void *memmove(void *dest, const void *src, size_t count) +{ + if (dest < src || src + count <= dest) + return memcpy(dest, src, count); + + if (dest > src) { + const char *s = src + count; + char *tmp = dest + count; + + while (count--) + *--tmp = *--s; + } + return dest; +} +EXPORT_SYMBOL(memmove); + +void *memset(void *s, int c, size_t count) +{ + union types dest = { .as_u8 = s }; + + if (count >= MIN_THRESHOLD) { + unsigned long cu = (unsigned long)c; + + /* Compose an ulong with 'c' repeated 4/8 times */ + cu |= cu << 8; + cu |= cu << 16; + /* Suppress warning on 32 bit machines */ + cu |= (cu << 16) << 16; + + for (; count && dest.as_uptr & WORD_MASK; count--) + *dest.as_u8++ = c; + + /* Copy using the largest size allowed */ + for (; count >= BYTES_LONG; count -= BYTES_LONG) + *dest.as_ulong++ = cu; + } + + /* copy the remainder */ + while (count--) + *dest.as_u8++ = c; + + return s; +} +EXPORT_SYMBOL(memset); |