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// Adapted from https://github.com/lemire/fastvalidate-utf-8
#ifdef __x86_64__
#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 print128(const char *s, const __m128i *v128)
{
const unsigned char *v8 = (const unsigned char *)v128;
if (s)
printf("%s: ", s);
for (int i = 0; i < 16; i++)
printf("%02x ", v8[i]);
printf("\n");
}
#endif
// all byte values must be no larger than 0xF4
static inline void checkSmallerThan0xF4(__m128i current_bytes,
__m128i *has_error) {
// unsigned, saturates to 0 below max
*has_error = _mm_or_si128(*has_error,
_mm_subs_epu8(current_bytes, _mm_set1_epi8(0xF4)));
}
static inline __m128i continuationLengths(__m128i high_nibbles) {
return _mm_shuffle_epi8(
_mm_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)
high_nibbles);
}
static inline __m128i carryContinuations(__m128i initial_lengths,
__m128i previous_carries) {
__m128i right1 =
_mm_subs_epu8(_mm_alignr_epi8(initial_lengths, previous_carries, 16 - 1),
_mm_set1_epi8(1));
__m128i sum = _mm_add_epi8(initial_lengths, right1);
__m128i right2 = _mm_subs_epu8(_mm_alignr_epi8(sum, previous_carries, 16 - 2),
_mm_set1_epi8(2));
return _mm_add_epi8(sum, right2);
}
static inline void checkContinuations(__m128i initial_lengths, __m128i carries,
__m128i *has_error) {
// overlap || underlap
// carry > length && length > 0 || !(carry > length) && !(length > 0)
// (carries > length) == (lengths > 0)
__m128i overunder =
_mm_cmpeq_epi8(_mm_cmpgt_epi8(carries, initial_lengths),
_mm_cmpgt_epi8(initial_lengths, _mm_setzero_si128()));
*has_error = _mm_or_si128(*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 checkFirstContinuationMax(__m128i current_bytes,
__m128i off1_current_bytes,
__m128i *has_error) {
__m128i maskED = _mm_cmpeq_epi8(off1_current_bytes, _mm_set1_epi8(0xED));
__m128i maskF4 = _mm_cmpeq_epi8(off1_current_bytes, _mm_set1_epi8(0xF4));
__m128i badfollowED =
_mm_and_si128(_mm_cmpgt_epi8(current_bytes, _mm_set1_epi8(0x9F)), maskED);
__m128i badfollowF4 =
_mm_and_si128(_mm_cmpgt_epi8(current_bytes, _mm_set1_epi8(0x8F)), maskF4);
*has_error = _mm_or_si128(*has_error, _mm_or_si128(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 checkOverlong(__m128i current_bytes,
__m128i off1_current_bytes, __m128i hibits,
__m128i previous_hibits, __m128i *has_error) {
__m128i off1_hibits = _mm_alignr_epi8(hibits, previous_hibits, 16 - 1);
__m128i initial_mins = _mm_shuffle_epi8(
_mm_setr_epi8(-128, -128, -128, -128, -128, -128, -128, -128, -128, -128,
-128, -128, // 10xx => false
0xC2, -128, // 110x
0xE1, // 1110
0xF1),
off1_hibits);
__m128i initial_under = _mm_cmpgt_epi8(initial_mins, off1_current_bytes);
__m128i second_mins = _mm_shuffle_epi8(
_mm_setr_epi8(-128, -128, -128, -128, -128, -128, -128, -128, -128, -128,
-128, -128, // 10xx => false
127, 127, // 110x => true
0xA0, // 1110
0x90),
off1_hibits);
__m128i second_under = _mm_cmpgt_epi8(second_mins, current_bytes);
*has_error =
_mm_or_si128(*has_error, _mm_and_si128(initial_under, second_under));
}
struct processed_utf_bytes {
__m128i rawbytes;
__m128i high_nibbles;
__m128i carried_continuations;
};
static inline void count_nibbles(__m128i bytes,
struct processed_utf_bytes *answer) {
answer->rawbytes = bytes;
answer->high_nibbles =
_mm_and_si128(_mm_srli_epi16(bytes, 4), _mm_set1_epi8(0x0F));
}
// check whether the current bytes are valid UTF-8
// at the end of the function, previous gets updated
static inline struct processed_utf_bytes
checkUTF8Bytes(__m128i current_bytes, struct processed_utf_bytes *previous,
__m128i *has_error) {
struct processed_utf_bytes pb;
count_nibbles(current_bytes, &pb);
checkSmallerThan0xF4(current_bytes, has_error);
__m128i initial_lengths = continuationLengths(pb.high_nibbles);
pb.carried_continuations =
carryContinuations(initial_lengths, previous->carried_continuations);
checkContinuations(initial_lengths, pb.carried_continuations, has_error);
__m128i off1_current_bytes =
_mm_alignr_epi8(pb.rawbytes, previous->rawbytes, 16 - 1);
checkFirstContinuationMax(current_bytes, off1_current_bytes, has_error);
checkOverlong(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(const unsigned char *src, int len) {
size_t i = 0;
__m128i has_error = _mm_setzero_si128();
struct processed_utf_bytes previous = {.rawbytes = _mm_setzero_si128(),
.high_nibbles = _mm_setzero_si128(),
.carried_continuations =
_mm_setzero_si128()};
if (len >= 16) {
for (; i <= len - 16; i += 16) {
__m128i current_bytes = _mm_loadu_si128((const __m128i *)(src + i));
previous = checkUTF8Bytes(current_bytes, &previous, &has_error);
}
}
// last part
if (i < len) {
char buffer[16];
memset(buffer, 0, 16);
memcpy(buffer, src + i, len - i);
__m128i current_bytes = _mm_loadu_si128((const __m128i *)(buffer));
previous = checkUTF8Bytes(current_bytes, &previous, &has_error);
} else {
has_error =
_mm_or_si128(_mm_cmpgt_epi8(previous.carried_continuations,
_mm_setr_epi8(9, 9, 9, 9, 9, 9, 9, 9, 9, 9,
9, 9, 9, 9, 9, 1)),
has_error);
}
return _mm_testz_si128(has_error, has_error) ? 0 : -1;
}
#endif
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