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lemire-avx2.c
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// Adapted from https://github.com/lemire/fastvalidate-utf-8
#ifdef __AVX2__
#include <stdio.h>
#include <stddef.h>
#include <stdint.h>
#include <string.h>
#include <x86intrin.h>
/*
* legal utf-8 byte sequence
* http://www.unicode.org/versions/Unicode6.0.0/ch03.pdf - page 94
*
* Code Points 1st 2s 3s 4s
* U+0000..U+007F 00..7F
* U+0080..U+07FF C2..DF 80..BF
* U+0800..U+0FFF E0 A0..BF 80..BF
* U+1000..U+CFFF E1..EC 80..BF 80..BF
* U+D000..U+D7FF ED 80..9F 80..BF
* U+E000..U+FFFF EE..EF 80..BF 80..BF
* U+10000..U+3FFFF F0 90..BF 80..BF 80..BF
* U+40000..U+FFFFF F1..F3 80..BF 80..BF 80..BF
* U+100000..U+10FFFF F4 80..8F 80..BF 80..BF
*
*/
#if 0
static void print256(const char *s, const __m256i v256)
{
const unsigned char *v8 = (const unsigned char *)&v256;
if (s)
printf("%s:\t", s);
for (int i = 0; i < 32; i++)
printf("%02x ", v8[i]);
printf("\n");
}
#endif
static inline __m256i push_last_byte_of_a_to_b(__m256i a, __m256i b) {
return _mm256_alignr_epi8(b, _mm256_permute2x128_si256(a, b, 0x21), 15);
}
static inline __m256i push_last_2bytes_of_a_to_b(__m256i a, __m256i b) {
return _mm256_alignr_epi8(b, _mm256_permute2x128_si256(a, b, 0x21), 14);
}
// all byte values must be no larger than 0xF4
static inline void avxcheckSmallerThan0xF4(__m256i current_bytes,
__m256i *has_error) {
// unsigned, saturates to 0 below max
*has_error = _mm256_or_si256(
*has_error, _mm256_subs_epu8(current_bytes, _mm256_set1_epi8(0xF4)));
}
static inline __m256i avxcontinuationLengths(__m256i high_nibbles) {
return _mm256_shuffle_epi8(
_mm256_setr_epi8(1, 1, 1, 1, 1, 1, 1, 1, // 0xxx (ASCII)
0, 0, 0, 0, // 10xx (continuation)
2, 2, // 110x
3, // 1110
4, // 1111, next should be 0 (not checked here)
1, 1, 1, 1, 1, 1, 1, 1, // 0xxx (ASCII)
0, 0, 0, 0, // 10xx (continuation)
2, 2, // 110x
3, // 1110
4 // 1111, next should be 0 (not checked here)
),
high_nibbles);
}
static inline __m256i avxcarryContinuations(__m256i initial_lengths,
__m256i previous_carries) {
__m256i right1 = _mm256_subs_epu8(
push_last_byte_of_a_to_b(previous_carries, initial_lengths),
_mm256_set1_epi8(1));
__m256i sum = _mm256_add_epi8(initial_lengths, right1);
__m256i right2 = _mm256_subs_epu8(
push_last_2bytes_of_a_to_b(previous_carries, sum), _mm256_set1_epi8(2));
return _mm256_add_epi8(sum, right2);
}
static inline void avxcheckContinuations(__m256i initial_lengths,
__m256i carries, __m256i *has_error) {
// overlap || underlap
// carry > length && length > 0 || !(carry > length) && !(length > 0)
// (carries > length) == (lengths > 0)
__m256i overunder = _mm256_cmpeq_epi8(
_mm256_cmpgt_epi8(carries, initial_lengths),
_mm256_cmpgt_epi8(initial_lengths, _mm256_setzero_si256()));
*has_error = _mm256_or_si256(*has_error, overunder);
}
// when 0xED is found, next byte must be no larger than 0x9F
// when 0xF4 is found, next byte must be no larger than 0x8F
// next byte must be continuation, ie sign bit is set, so signed < is ok
static inline void avxcheckFirstContinuationMax(__m256i current_bytes,
__m256i off1_current_bytes,
__m256i *has_error) {
__m256i maskED =
_mm256_cmpeq_epi8(off1_current_bytes, _mm256_set1_epi8(0xED));
__m256i maskF4 =
_mm256_cmpeq_epi8(off1_current_bytes, _mm256_set1_epi8(0xF4));
__m256i badfollowED = _mm256_and_si256(
_mm256_cmpgt_epi8(current_bytes, _mm256_set1_epi8(0x9F)), maskED);
__m256i badfollowF4 = _mm256_and_si256(
_mm256_cmpgt_epi8(current_bytes, _mm256_set1_epi8(0x8F)), maskF4);
*has_error =
_mm256_or_si256(*has_error, _mm256_or_si256(badfollowED, badfollowF4));
}
// map off1_hibits => error condition
// hibits off1 cur
// C => < C2 && true
// E => < E1 && < A0
// F => < F1 && < 90
// else false && false
static inline void avxcheckOverlong(__m256i current_bytes,
__m256i off1_current_bytes, __m256i hibits,
__m256i previous_hibits,
__m256i *has_error) {
__m256i off1_hibits = push_last_byte_of_a_to_b(previous_hibits, hibits);
__m256i initial_mins = _mm256_shuffle_epi8(
_mm256_setr_epi8(-128, -128, -128, -128, -128, -128, -128, -128, -128,
-128, -128, -128, // 10xx => false
0xC2, -128, // 110x
0xE1, // 1110
0xF1, -128, -128, -128, -128, -128, -128, -128, -128,
-128, -128, -128, -128, // 10xx => false
0xC2, -128, // 110x
0xE1, // 1110
0xF1),
off1_hibits);
__m256i initial_under = _mm256_cmpgt_epi8(initial_mins, off1_current_bytes);
__m256i second_mins = _mm256_shuffle_epi8(
_mm256_setr_epi8(-128, -128, -128, -128, -128, -128, -128, -128, -128,
-128, -128, -128, // 10xx => false
127, 127, // 110x => true
0xA0, // 1110
0x90, -128, -128, -128, -128, -128, -128, -128, -128,
-128, -128, -128, -128, // 10xx => false
127, 127, // 110x => true
0xA0, // 1110
0x90),
off1_hibits);
__m256i second_under = _mm256_cmpgt_epi8(second_mins, current_bytes);
*has_error = _mm256_or_si256(*has_error,
_mm256_and_si256(initial_under, second_under));
}
struct avx_processed_utf_bytes {
__m256i rawbytes;
__m256i high_nibbles;
__m256i carried_continuations;
};
static inline void avx_count_nibbles(__m256i bytes,
struct avx_processed_utf_bytes *answer) {
answer->rawbytes = bytes;
answer->high_nibbles =
_mm256_and_si256(_mm256_srli_epi16(bytes, 4), _mm256_set1_epi8(0x0F));
}
// check whether the current bytes are valid UTF-8
// at the end of the function, previous gets updated
static struct avx_processed_utf_bytes
avxcheckUTF8Bytes(__m256i current_bytes,
struct avx_processed_utf_bytes *previous,
__m256i *has_error) {
struct avx_processed_utf_bytes pb;
avx_count_nibbles(current_bytes, &pb);
avxcheckSmallerThan0xF4(current_bytes, has_error);
__m256i initial_lengths = avxcontinuationLengths(pb.high_nibbles);
pb.carried_continuations =
avxcarryContinuations(initial_lengths, previous->carried_continuations);
avxcheckContinuations(initial_lengths, pb.carried_continuations, has_error);
__m256i off1_current_bytes =
push_last_byte_of_a_to_b(previous->rawbytes, pb.rawbytes);
avxcheckFirstContinuationMax(current_bytes, off1_current_bytes, has_error);
avxcheckOverlong(current_bytes, off1_current_bytes, pb.high_nibbles,
previous->high_nibbles, has_error);
return pb;
}
/* Return 0 on success, -1 on error */
int utf8_lemire_avx2(const unsigned char *src, int len) {
size_t i = 0;
__m256i has_error = _mm256_setzero_si256();
struct avx_processed_utf_bytes previous = {
.rawbytes = _mm256_setzero_si256(),
.high_nibbles = _mm256_setzero_si256(),
.carried_continuations = _mm256_setzero_si256()};
if (len >= 32) {
for (; i <= len - 32; i += 32) {
__m256i current_bytes = _mm256_loadu_si256((const __m256i *)(src + i));
previous = avxcheckUTF8Bytes(current_bytes, &previous, &has_error);
}
}
// last part
if (i < len) {
char buffer[32];
memset(buffer, 0, 32);
memcpy(buffer, src + i, len - i);
__m256i current_bytes = _mm256_loadu_si256((const __m256i *)(buffer));
previous = avxcheckUTF8Bytes(current_bytes, &previous, &has_error);
} else {
has_error = _mm256_or_si256(
_mm256_cmpgt_epi8(previous.carried_continuations,
_mm256_setr_epi8(9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9,
9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9,
9, 9, 9, 9, 9, 9, 9, 1)),
has_error);
}
return _mm256_testz_si256(has_error, has_error) ? 0 : -1;
}
#endif