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#include <stdlib.h>
// WARNING: When building the scalar versions of these functions you need to
// use the compiler flag "-mllvm -disable-loop-idiom-all" to prevent clang
// from recognising a loop idiom and planting calls to memcpy!
static void *__arm_sc_memcpy_fwd(void *dest, const void *src,
size_t n) __arm_streaming_compatible {
unsigned char *destp = (unsigned char *)dest;
const unsigned char *srcp = (const unsigned char *)src;
for (size_t i = 0; i < n; ++i)
destp[i] = srcp[i];
return dest;
}
// If dest and src overlap then behaviour is undefined, hence we can add the
// restrict keywords here. This also matches the definition of the libc memcpy
// according to the man page.
void *__arm_sc_memcpy(void *__restrict__ dest, const void *__restrict__ src,
size_t n) __arm_streaming_compatible {
return __arm_sc_memcpy_fwd(dest, src, n);
}
void *__arm_sc_memset(void *dest, int c, size_t n) __arm_streaming_compatible {
unsigned char *destp = (unsigned char *)dest;
unsigned char c8 = (unsigned char)c;
for (size_t i = 0; i < n; ++i)
destp[i] = c8;
return dest;
}
static void *__arm_sc_memcpy_rev(void *dest, const void *src,
size_t n) __arm_streaming_compatible {
unsigned char *destp = (unsigned char *)dest;
const unsigned char *srcp = (const unsigned char *)src;
// TODO: Improve performance by copying larger chunks in reverse, or by
// using SVE.
while (n > 0) {
--n;
destp[n] = srcp[n];
}
return dest;
}
// Semantically a memmove is equivalent to the following:
// 1. Copy the entire contents of src to a temporary array that does not
// overlap with src or dest.
// 2. Copy the contents of the temporary array into dest.
void *__arm_sc_memmove(void *dest, const void *src,
size_t n) __arm_streaming_compatible {
unsigned char *destp = (unsigned char *)dest;
const unsigned char *srcp = (const unsigned char *)src;
// If src and dest don't overlap then just invoke memcpy
if ((srcp > (destp + n)) || (destp > (srcp + n)))
return __arm_sc_memcpy_fwd(dest, src, n);
// Overlap case 1:
// src: Low | -> | High
// dest: Low | -> | High
// Here src is always ahead of dest at a higher addres. If we first read a
// chunk of data from src we can safely write the same chunk to dest without
// corrupting future reads of src.
if (srcp > destp)
return __arm_sc_memcpy_fwd(dest, src, n);
// Overlap case 2:
// src: Low | -> | High
// dest: Low | -> | High
// While we're in the overlap region we're always corrupting future reads of
// src when writing to dest. An efficient way to do this is to copy the data
// in reverse by starting at the highest address.
return __arm_sc_memcpy_rev(dest, src, n);
}
const void *__arm_sc_memchr(const void *src, int c,
size_t n) __arm_streaming_compatible {
const unsigned char *srcp = (const unsigned char *)src;
unsigned char c8 = (unsigned char)c;
for (size_t i = 0; i < n; ++i)
if (srcp[i] == c8)
return &srcp[i];
return NULL;
}
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