lnav/src/simdutf8check.h

/**
 * https://github.com/lemire/fastvalidate-utf-8
 */

#ifndef SIMDUTF8CHECK_H
#define SIMDUTF8CHECK_H
#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>
#include <x86intrin.h>

#include "base/lnav_log.hh"

#ifdef __cplusplus
extern "C" {
#endif

/*
 * 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
 *
 */

// all byte values must be no larger than 0xF4
static 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 __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 __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 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 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 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 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 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;
}

static bool validate_utf8_fast(const char *src, size_t len, ssize_t *len_out)
{
    size_t i = 0, orig_len = len;
    __m128i has_error = _mm_setzero_si128();
    __m128i lfchars = _mm_set1_epi8('\n');
    __m128i lfresult = _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);
            lfresult = _mm_cmpeq_epi8(current_bytes, lfchars);
            if (_mm_movemask_epi8(lfresult)) {
                for (; src[i] != '\n'; i++) {
                }
                len = i;
                break;
            }
        }
    }

    //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);
        for (; i < len && src[i] != '\n'; i++) {
        }
    } 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);
    }

    if (i < orig_len && src[i] == '\n') {
        *len_out = i;
    }

    return _mm_testz_si128(has_error, has_error);
}

#ifdef __cplusplus
}
#endif

#endif