1 // Adapted from https://github.com/lemire/fastvalidate-utf-8
2
3 #ifdef __x86_64__
4
5 #include <stdio.h>
6 #include <stddef.h>
7 #include <stdint.h>
8 #include <string.h>
9 #include <x86intrin.h>
10
11 /*
12 * legal utf-8 byte sequence
13 * http://www.unicode.org/versions/Unicode6.0.0/ch03.pdf - page 94
14 *
15 * Code Points 1st 2s 3s 4s
16 * U+0000..U+007F 00..7F
17 * U+0080..U+07FF C2..DF 80..BF
18 * U+0800..U+0FFF E0 A0..BF 80..BF
19 * U+1000..U+CFFF E1..EC 80..BF 80..BF
20 * U+D000..U+D7FF ED 80..9F 80..BF
21 * U+E000..U+FFFF EE..EF 80..BF 80..BF
22 * U+10000..U+3FFFF F0 90..BF 80..BF 80..BF
23 * U+40000..U+FFFFF F1..F3 80..BF 80..BF 80..BF
24 * U+100000..U+10FFFF F4 80..8F 80..BF 80..BF
25 *
26 */
27
28 #if 0
29 static void print128(const char *s, const __m128i *v128)
30 {
31 const unsigned char *v8 = (const unsigned char *)v128;
32 if (s)
33 printf("%s: ", s);
34 for (int i = 0; i < 16; i++)
35 printf("%02x ", v8[i]);
36 printf("\n");
37 }
38 #endif
39
40 // all byte values must be no larger than 0xF4
checkSmallerThan0xF4(__m128i current_bytes,__m128i * has_error)41 static inline void checkSmallerThan0xF4(__m128i current_bytes,
42 __m128i *has_error) {
43 // unsigned, saturates to 0 below max
44 *has_error = _mm_or_si128(*has_error,
45 _mm_subs_epu8(current_bytes, _mm_set1_epi8(0xF4)));
46 }
47
continuationLengths(__m128i high_nibbles)48 static inline __m128i continuationLengths(__m128i high_nibbles) {
49 return _mm_shuffle_epi8(
50 _mm_setr_epi8(1, 1, 1, 1, 1, 1, 1, 1, // 0xxx (ASCII)
51 0, 0, 0, 0, // 10xx (continuation)
52 2, 2, // 110x
53 3, // 1110
54 4), // 1111, next should be 0 (not checked here)
55 high_nibbles);
56 }
57
carryContinuations(__m128i initial_lengths,__m128i previous_carries)58 static inline __m128i carryContinuations(__m128i initial_lengths,
59 __m128i previous_carries) {
60
61 __m128i right1 =
62 _mm_subs_epu8(_mm_alignr_epi8(initial_lengths, previous_carries, 16 - 1),
63 _mm_set1_epi8(1));
64 __m128i sum = _mm_add_epi8(initial_lengths, right1);
65
66 __m128i right2 = _mm_subs_epu8(_mm_alignr_epi8(sum, previous_carries, 16 - 2),
67 _mm_set1_epi8(2));
68 return _mm_add_epi8(sum, right2);
69 }
70
checkContinuations(__m128i initial_lengths,__m128i carries,__m128i * has_error)71 static inline void checkContinuations(__m128i initial_lengths, __m128i carries,
72 __m128i *has_error) {
73
74 // overlap || underlap
75 // carry > length && length > 0 || !(carry > length) && !(length > 0)
76 // (carries > length) == (lengths > 0)
77 __m128i overunder =
78 _mm_cmpeq_epi8(_mm_cmpgt_epi8(carries, initial_lengths),
79 _mm_cmpgt_epi8(initial_lengths, _mm_setzero_si128()));
80
81 *has_error = _mm_or_si128(*has_error, overunder);
82 }
83
84 // when 0xED is found, next byte must be no larger than 0x9F
85 // when 0xF4 is found, next byte must be no larger than 0x8F
86 // next byte must be continuation, ie sign bit is set, so signed < is ok
checkFirstContinuationMax(__m128i current_bytes,__m128i off1_current_bytes,__m128i * has_error)87 static inline void checkFirstContinuationMax(__m128i current_bytes,
88 __m128i off1_current_bytes,
89 __m128i *has_error) {
90 __m128i maskED = _mm_cmpeq_epi8(off1_current_bytes, _mm_set1_epi8(0xED));
91 __m128i maskF4 = _mm_cmpeq_epi8(off1_current_bytes, _mm_set1_epi8(0xF4));
92
93 __m128i badfollowED =
94 _mm_and_si128(_mm_cmpgt_epi8(current_bytes, _mm_set1_epi8(0x9F)), maskED);
95 __m128i badfollowF4 =
96 _mm_and_si128(_mm_cmpgt_epi8(current_bytes, _mm_set1_epi8(0x8F)), maskF4);
97
98 *has_error = _mm_or_si128(*has_error, _mm_or_si128(badfollowED, badfollowF4));
99 }
100
101 // map off1_hibits => error condition
102 // hibits off1 cur
103 // C => < C2 && true
104 // E => < E1 && < A0
105 // F => < F1 && < 90
106 // else false && false
checkOverlong(__m128i current_bytes,__m128i off1_current_bytes,__m128i hibits,__m128i previous_hibits,__m128i * has_error)107 static inline void checkOverlong(__m128i current_bytes,
108 __m128i off1_current_bytes, __m128i hibits,
109 __m128i previous_hibits, __m128i *has_error) {
110 __m128i off1_hibits = _mm_alignr_epi8(hibits, previous_hibits, 16 - 1);
111 __m128i initial_mins = _mm_shuffle_epi8(
112 _mm_setr_epi8(-128, -128, -128, -128, -128, -128, -128, -128, -128, -128,
113 -128, -128, // 10xx => false
114 0xC2, -128, // 110x
115 0xE1, // 1110
116 0xF1),
117 off1_hibits);
118
119 __m128i initial_under = _mm_cmpgt_epi8(initial_mins, off1_current_bytes);
120
121 __m128i second_mins = _mm_shuffle_epi8(
122 _mm_setr_epi8(-128, -128, -128, -128, -128, -128, -128, -128, -128, -128,
123 -128, -128, // 10xx => false
124 127, 127, // 110x => true
125 0xA0, // 1110
126 0x90),
127 off1_hibits);
128 __m128i second_under = _mm_cmpgt_epi8(second_mins, current_bytes);
129 *has_error =
130 _mm_or_si128(*has_error, _mm_and_si128(initial_under, second_under));
131 }
132
133 struct processed_utf_bytes {
134 __m128i rawbytes;
135 __m128i high_nibbles;
136 __m128i carried_continuations;
137 };
138
count_nibbles(__m128i bytes,struct processed_utf_bytes * answer)139 static inline void count_nibbles(__m128i bytes,
140 struct processed_utf_bytes *answer) {
141 answer->rawbytes = bytes;
142 answer->high_nibbles =
143 _mm_and_si128(_mm_srli_epi16(bytes, 4), _mm_set1_epi8(0x0F));
144 }
145
146 // check whether the current bytes are valid UTF-8
147 // at the end of the function, previous gets updated
148 static inline struct processed_utf_bytes
checkUTF8Bytes(__m128i current_bytes,struct processed_utf_bytes * previous,__m128i * has_error)149 checkUTF8Bytes(__m128i current_bytes, struct processed_utf_bytes *previous,
150 __m128i *has_error) {
151
152 struct processed_utf_bytes pb;
153 count_nibbles(current_bytes, &pb);
154
155 checkSmallerThan0xF4(current_bytes, has_error);
156
157 __m128i initial_lengths = continuationLengths(pb.high_nibbles);
158
159 pb.carried_continuations =
160 carryContinuations(initial_lengths, previous->carried_continuations);
161
162 checkContinuations(initial_lengths, pb.carried_continuations, has_error);
163
164 __m128i off1_current_bytes =
165 _mm_alignr_epi8(pb.rawbytes, previous->rawbytes, 16 - 1);
166 checkFirstContinuationMax(current_bytes, off1_current_bytes, has_error);
167
168 checkOverlong(current_bytes, off1_current_bytes, pb.high_nibbles,
169 previous->high_nibbles, has_error);
170 return pb;
171 }
172
173 /* Return 0 on success, -1 on error */
utf8_lemire(const unsigned char * src,int len)174 int utf8_lemire(const unsigned char *src, int len) {
175 size_t i = 0;
176 __m128i has_error = _mm_setzero_si128();
177 struct processed_utf_bytes previous = {.rawbytes = _mm_setzero_si128(),
178 .high_nibbles = _mm_setzero_si128(),
179 .carried_continuations =
180 _mm_setzero_si128()};
181 if (len >= 16) {
182 for (; i <= len - 16; i += 16) {
183 __m128i current_bytes = _mm_loadu_si128((const __m128i *)(src + i));
184 previous = checkUTF8Bytes(current_bytes, &previous, &has_error);
185 }
186 }
187
188 // last part
189 if (i < len) {
190 char buffer[16];
191 memset(buffer, 0, 16);
192 memcpy(buffer, src + i, len - i);
193 __m128i current_bytes = _mm_loadu_si128((const __m128i *)(buffer));
194 previous = checkUTF8Bytes(current_bytes, &previous, &has_error);
195 } else {
196 has_error =
197 _mm_or_si128(_mm_cmpgt_epi8(previous.carried_continuations,
198 _mm_setr_epi8(9, 9, 9, 9, 9, 9, 9, 9, 9, 9,
199 9, 9, 9, 9, 9, 1)),
200 has_error);
201 }
202
203 return _mm_testz_si128(has_error, has_error) ? 0 : -1;
204 }
205
206 #endif
207