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