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/**
* SPDX-License-Identifier: GPL-3.0-or-later
* Copyright 2018 (C) Fabian Klötzl
*/
#include "seqcmp.h"
#include <assert.h>
#include <emmintrin.h>
#include <string.h>
typedef __m128i vec_type;
size_t seqcmp_sse2(const char *begin, const char *other, size_t length)
{
assert(begin != NULL);
assert(other != NULL);
size_t substitutions = 0;
const size_t vec_bytes = sizeof(vec_type);
size_t vec_offset = 0;
size_t vec_length = (length / vec_bytes) & ~(size_t)1; // round down
size_t equal = 0;
for (; vec_offset < vec_length; vec_offset++) {
vec_type begin_chunk;
vec_type other_chunk;
memcpy(&begin_chunk, begin + vec_offset * vec_bytes, vec_bytes);
memcpy(&other_chunk, other + vec_offset * vec_bytes, vec_bytes);
vec_type comp = _mm_cmpeq_epi8(begin_chunk, other_chunk);
unsigned int vmask = _mm_movemask_epi8(comp);
equal += __builtin_popcount(vmask);
vec_offset++;
// second pass
memcpy(&begin_chunk, begin + vec_offset * vec_bytes, vec_bytes);
memcpy(&other_chunk, other + vec_offset * vec_bytes, vec_bytes);
comp = _mm_cmpeq_epi8(begin_chunk, other_chunk);
vmask = _mm_movemask_epi8(comp);
equal += __builtin_popcount(vmask);
}
substitutions = vec_offset * vec_bytes - equal;
size_t offset = vec_offset * vec_bytes;
for (; offset < length; offset++) {
if (begin[offset] != other[offset]) {
substitutions++;
}
}
return substitutions;
}
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