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// Adapted from https://github.com/lemire/fastvalidate-utf-8
#ifdef __aarch64__
#include <stdio.h>
#include <stddef.h>
#include <stdint.h>
#include <string.h>
#include <inttypes.h>
#include <arm_neon.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 int8x16_t *v128)
{
int8_t v8[16];
vst1q_s8(v8, *v128);
if (s)
printf("%s:\t", s);
for (int i = 0; i < 16; ++i)
printf("%02x ", (unsigned char)v8[i]);
printf("\n");
}
#endif
// all byte values must be no larger than 0xF4
static inline void checkSmallerThan0xF4(int8x16_t current_bytes,
int8x16_t *has_error) {
// unsigned, saturates to 0 below max
*has_error = vorrq_s8(*has_error,
vreinterpretq_s8_u8(vqsubq_u8(vreinterpretq_u8_s8(current_bytes), vdupq_n_u8(0xF4))));
}
static const int8_t _nibbles[] = {
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)
};
static inline int8x16_t continuationLengths(int8x16_t high_nibbles) {
return vqtbl1q_s8(vld1q_s8(_nibbles), vreinterpretq_u8_s8(high_nibbles));
}
static inline int8x16_t carryContinuations(int8x16_t initial_lengths,
int8x16_t previous_carries) {
int8x16_t right1 =
vreinterpretq_s8_u8(vqsubq_u8(vreinterpretq_u8_s8(vextq_s8(previous_carries, initial_lengths, 16 - 1)),
vdupq_n_u8(1)));
int8x16_t sum = vaddq_s8(initial_lengths, right1);
int8x16_t right2 = vreinterpretq_s8_u8(vqsubq_u8(vreinterpretq_u8_s8(vextq_s8(previous_carries, sum, 16 - 2)),
vdupq_n_u8(2)));
return vaddq_s8(sum, right2);
}
static inline void checkContinuations(int8x16_t initial_lengths, int8x16_t carries,
int8x16_t *has_error) {
// overlap || underlap
// carry > length && length > 0 || !(carry > length) && !(length > 0)
// (carries > length) == (lengths > 0)
uint8x16_t overunder =
vceqq_u8(vcgtq_s8(carries, initial_lengths),
vcgtq_s8(initial_lengths, vdupq_n_s8(0)));
*has_error = vorrq_s8(*has_error, vreinterpretq_s8_u8(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(int8x16_t current_bytes,
int8x16_t off1_current_bytes,
int8x16_t *has_error) {
uint8x16_t maskED = vceqq_s8(off1_current_bytes, vdupq_n_s8(0xED));
uint8x16_t maskF4 = vceqq_s8(off1_current_bytes, vdupq_n_s8(0xF4));
uint8x16_t badfollowED =
vandq_u8(vcgtq_s8(current_bytes, vdupq_n_s8(0x9F)), maskED);
uint8x16_t badfollowF4 =
vandq_u8(vcgtq_s8(current_bytes, vdupq_n_s8(0x8F)), maskF4);
*has_error = vorrq_s8(*has_error, vreinterpretq_s8_u8(vorrq_u8(badfollowED, badfollowF4)));
}
static const int8_t _initial_mins[] = {
-128, -128, -128, -128, -128, -128, -128, -128, -128, -128,
-128, -128, // 10xx => false
0xC2, -128, // 110x
0xE1, // 1110
0xF1,
};
static const int8_t _second_mins[] = {
-128, -128, -128, -128, -128, -128, -128, -128, -128, -128,
-128, -128, // 10xx => false
127, 127, // 110x => true
0xA0, // 1110
0x90,
};
// map off1_hibits => error condition
// hibits off1 cur
// C => < C2 && true
// E => < E1 && < A0
// F => < F1 && < 90
// else false && false
static inline void checkOverlong(int8x16_t current_bytes,
int8x16_t off1_current_bytes, int8x16_t hibits,
int8x16_t previous_hibits, int8x16_t *has_error) {
int8x16_t off1_hibits = vextq_s8(previous_hibits, hibits, 16 - 1);
int8x16_t initial_mins = vqtbl1q_s8(vld1q_s8(_initial_mins), vreinterpretq_u8_s8(off1_hibits));
uint8x16_t initial_under = vcgtq_s8(initial_mins, off1_current_bytes);
int8x16_t second_mins = vqtbl1q_s8(vld1q_s8(_second_mins), vreinterpretq_u8_s8(off1_hibits));
uint8x16_t second_under = vcgtq_s8(second_mins, current_bytes);
*has_error =
vorrq_s8(*has_error, vreinterpretq_s8_u8(vandq_u8(initial_under, second_under)));
}
struct processed_utf_bytes {
int8x16_t rawbytes;
int8x16_t high_nibbles;
int8x16_t carried_continuations;
};
static inline void count_nibbles(int8x16_t bytes,
struct processed_utf_bytes *answer) {
answer->rawbytes = bytes;
answer->high_nibbles =
vreinterpretq_s8_u8(vshrq_n_u8(vreinterpretq_u8_s8(bytes), 4));
}
// 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(int8x16_t current_bytes, struct processed_utf_bytes *previous,
int8x16_t *has_error) {
struct processed_utf_bytes pb;
count_nibbles(current_bytes, &pb);
checkSmallerThan0xF4(current_bytes, has_error);
int8x16_t initial_lengths = continuationLengths(pb.high_nibbles);
pb.carried_continuations =
carryContinuations(initial_lengths, previous->carried_continuations);
checkContinuations(initial_lengths, pb.carried_continuations, has_error);
int8x16_t off1_current_bytes =
vextq_s8(previous->rawbytes, pb.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;
}
static const int8_t _verror[] = {9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 1};
/* Return 0 on success, -1 on error */
int utf8_lemire(const unsigned char *src, int len) {
size_t i = 0;
int8x16_t has_error = vdupq_n_s8(0);
struct processed_utf_bytes previous = {.rawbytes = vdupq_n_s8(0),
.high_nibbles = vdupq_n_s8(0),
.carried_continuations =
vdupq_n_s8(0)};
if (len >= 16) {
for (; i <= len - 16; i += 16) {
int8x16_t current_bytes = vld1q_s8((int8_t*)(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);
int8x16_t current_bytes = vld1q_s8((int8_t *)buffer);
previous = checkUTF8Bytes(current_bytes, &previous, &has_error);
} else {
has_error =
vorrq_s8(vreinterpretq_s8_u8(vcgtq_s8(previous.carried_continuations,
vld1q_s8(_verror))),
has_error);
}
return vmaxvq_u8(vreinterpretq_u8_s8(has_error)) == 0 ? 0 : -1;
}
#endif
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