is_utf8 0.1.4

Provides functions to determine if a sequence of bytes is valid utf-8.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304

//! # SSE implementation of Lemire's algorithm
//!
//! ## Target specific intrinsics used:
//! ### SSE2
//! * _mm_add_epi8
//! * _mm_and_si128
//! * _mm_cmpeq_epi8
//! * _mm_cmpgt_epi8
//! * _mm_loadu_si128
//! * _mm_or_si128
//! * _mm_set1_epi8
//! * _mm_set_epi8
//! * _mm_setr_epi8
//! * _mm_setzero_si128
//! * _mm_srli_epi16
//! * _mm_subs_epu8
//!
//! ### SSSE3
//! * _mm_alignr_epi8
//! * _mm_shuffle_epi8
//!
//! ### SSE4.1
//! * _mm_testz_si128

/*
 * 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
 *
 */
#[cfg(target_arch = "x86")]
use core::arch::x86::{
    __m128i, _mm_add_epi8, _mm_alignr_epi8, _mm_and_si128, _mm_cmpeq_epi8, _mm_cmpgt_epi8,
    _mm_loadu_si128, _mm_or_si128, _mm_set1_epi8, _mm_set_epi8, _mm_setr_epi8, _mm_setzero_si128,
    _mm_shuffle_epi8, _mm_srli_epi16, _mm_subs_epu8, _mm_testz_si128,
};
#[cfg(target_arch = "x86_64")]
use core::arch::x86_64::{
    __m128i, _mm_add_epi8, _mm_alignr_epi8, _mm_and_si128, _mm_cmpeq_epi8, _mm_cmpgt_epi8,
    _mm_loadu_si128, _mm_or_si128, _mm_set1_epi8, _mm_setr_epi8, _mm_setzero_si128,
    _mm_shuffle_epi8, _mm_srli_epi16, _mm_subs_epu8, _mm_testz_si128,
};
use core::default::Default;
use core::ptr;

#[derive(Copy, Clone)]
struct ProcessedUtfBytes {
    rawbytes: __m128i,
    high_nibbles: __m128i,
    carried_continuations: __m128i,
}

impl Default for ProcessedUtfBytes {
    fn default() -> Self {
        unsafe {
            ProcessedUtfBytes {
                rawbytes: _mm_setzero_si128(),
                high_nibbles: _mm_setzero_si128(),
                carried_continuations: _mm_setzero_si128(),
            }
        }
    }
}

impl ProcessedUtfBytes {
    #[inline]
    fn count_nibbles(&mut self, bytes: __m128i) {
        self.rawbytes = bytes;
        self.high_nibbles = unsafe { _mm_and_si128(_mm_srli_epi16(bytes, 4), _mm_set1_epi8(0xF)) };
    }
}

#[derive(Clone)]
struct State {
    previous: ProcessedUtfBytes,
    has_error: __m128i,
}

impl Default for State {
    fn default() -> Self {
        State {
            previous: ProcessedUtfBytes::default(),
            has_error: unsafe { _mm_setzero_si128() },
        }
    }
}

impl State {
    // check whether the current bytes are valid UTF-8
    // at the end of the function, previous gets updated
    fn check_bytes(&mut self, current_bytes: __m128i) {
        let mut pb = ProcessedUtfBytes::default();
        pb.count_nibbles(current_bytes);
        self.check_smaller_than_0xf4(current_bytes);
        let initial_lengths = continuation_lengths(pb.high_nibbles);
        pb.carried_continuations =
            carry_continuations(initial_lengths, self.previous.carried_continuations);
        self.check_continuations(initial_lengths, pb.carried_continuations);
        let current_bytes_off_by_one =
            unsafe { _mm_alignr_epi8(pb.rawbytes, self.previous.rawbytes, 16 - 1) };
        self.check_first_continuation_max(current_bytes, current_bytes_off_by_one);
        self.check_overlong(
            current_bytes,
            current_bytes_off_by_one,
            pb.high_nibbles,
            self.previous.high_nibbles,
        );
        self.previous = pb;
    }

    // all byte values must be no larger than 0xF4
    #[inline]
    fn check_smaller_than_0xf4(&mut self, current_bytes: __m128i) {
        unsafe {
            // unsigned, saturates to 0 below max
            self.has_error = _mm_or_si128(
                self.has_error,
                _mm_subs_epu8(current_bytes, _mm_set1_epi8(0xF4i32 as i8)),
            );
        }
    }

    // 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
    #[inline]
    fn check_first_continuation_max(
        &mut self,
        current_bytes: __m128i,
        off1_current_bytes: __m128i,
    ) {
        unsafe {
            let mask_ed = _mm_cmpeq_epi8(off1_current_bytes, _mm_set1_epi8(0xEDi32 as i8));
            let mask_f4 = _mm_cmpeq_epi8(off1_current_bytes, _mm_set1_epi8(0xF4i32 as i8));
            let bad_follow_ed = _mm_and_si128(
                _mm_cmpgt_epi8(current_bytes, _mm_set1_epi8(0x9Fi32 as i8)),
                mask_ed,
            );
            let bad_follow_f4 = _mm_and_si128(
                _mm_cmpgt_epi8(current_bytes, _mm_set1_epi8(0x8Fi32 as i8)),
                mask_f4,
            );
            self.has_error =
                _mm_or_si128(self.has_error, _mm_or_si128(bad_follow_ed, bad_follow_f4));
        }
    }

    #[inline]
    fn check_continuations(&mut self, initial_lengths: __m128i, carries: __m128i) {
        unsafe {
            let overunder = _mm_cmpeq_epi8(
                _mm_cmpgt_epi8(carries, initial_lengths),
                _mm_cmpgt_epi8(initial_lengths, _mm_setzero_si128()),
            );
            self.has_error = _mm_or_si128(self.has_error, overunder);
        }
    }

    // map off1_hibits => error condition
    // hibits     off1    cur
    // C       => < C2 && true
    // E       => < E1 && < A0
    // F       => < F1 && < 90
    // else      false && false
    #[inline]
    fn check_overlong(
        &mut self,
        current_bytes: __m128i,
        off1_current_bytes: __m128i,
        hibits: __m128i,
        previous_hibits: __m128i,
    ) {
        unsafe {
            let off1_hibits = _mm_alignr_epi8(hibits, previous_hibits, 16 - 1);
            let initial_mins = _mm_shuffle_epi8(
                _mm_setr_epi8(
                    -128,
                    -128,
                    -128,
                    -128,
                    -128,
                    -128,
                    -128,
                    -128,
                    -128,
                    -128,
                    -128,
                    -128,
                    0xC2i32 as i8,
                    -128,
                    0xE1i32 as i8,
                    0xF1i32 as i8,
                ),
                off1_hibits,
            );
            let initial_under = _mm_cmpgt_epi8(initial_mins, off1_current_bytes);
            let second_mins = _mm_shuffle_epi8(
                _mm_setr_epi8(
                    -128,
                    -128,
                    -128,
                    -128,
                    -128,
                    -128,
                    -128,
                    -128,
                    -128,
                    -128,
                    -128,
                    -128,
                    127,
                    127,
                    0xA0i32 as i8,
                    0x90i32 as i8,
                ),
                off1_hibits,
            );
            let second_under = _mm_cmpgt_epi8(second_mins, current_bytes);
            self.has_error =
                _mm_or_si128(self.has_error, _mm_and_si128(initial_under, second_under));
        }
    }

    fn is_erroneous(self) -> bool {
        unsafe { _mm_testz_si128(self.has_error, self.has_error) != 0 }
    }
}

#[inline]
fn continuation_lengths(high_nibbles: __m128i) -> __m128i {
    unsafe {
        _mm_shuffle_epi8(
            _mm_setr_epi8(1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 2, 2, 3, 4),
            high_nibbles,
        )
    }
}

#[inline]
fn carry_continuations(initial_lengths: __m128i, previous_carries: __m128i) -> __m128i {
    unsafe {
        let right1 = _mm_subs_epu8(
            _mm_alignr_epi8(initial_lengths, previous_carries, 16 - 1),
            _mm_set1_epi8(1),
        );
        let sum = _mm_add_epi8(initial_lengths, right1);
        let right2 = _mm_subs_epu8(
            _mm_alignr_epi8(sum, previous_carries, 16 - 2),
            _mm_set1_epi8(2),
        );
        _mm_add_epi8(sum, right2)
    }
}

pub fn is_utf8(bytes: &[u8]) -> bool {
    let len = bytes.len();
    let mut i = 0;

    let mut state = State::default();

    if len >= 16 {
        while i <= len - 16 {
            let current_bytes =
                unsafe { _mm_loadu_si128(bytes.as_ptr().offset(i as isize) as *const __m128i) };
            state.check_bytes(current_bytes);
            i += 16
        }
    }
    // last part
    if i < len {
        let mut buffer = [0; 16];
        unsafe {
            ptr::copy(
                bytes.as_ptr().offset(i as isize),
                buffer.as_mut_ptr(),
                len - i,
            );
            let current_bytes_0 = _mm_loadu_si128(buffer.as_mut_ptr() as *const __m128i);
            state.check_bytes(current_bytes_0);
        }
    } else {
        unsafe {
            state.has_error = _mm_or_si128(
                _mm_cmpgt_epi8(
                    state.previous.carried_continuations,
                    _mm_setr_epi8(9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 1),
                ),
                state.has_error,
            )
        }
    }

    state.is_erroneous()
}