Bug Summary

File:llvm/include/llvm/ADT/edit_distance.h
Warning:line 96, column 3
Assigned value is garbage or undefined

Annotated Source Code

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clang -cc1 -cc1 -triple x86_64-pc-linux-gnu -analyze -disable-free -disable-llvm-verifier -discard-value-names -main-file-name StringRef.cpp -analyzer-store=region -analyzer-opt-analyze-nested-blocks -analyzer-checker=core -analyzer-checker=apiModeling -analyzer-checker=unix -analyzer-checker=deadcode -analyzer-checker=cplusplus -analyzer-checker=security.insecureAPI.UncheckedReturn -analyzer-checker=security.insecureAPI.getpw -analyzer-checker=security.insecureAPI.gets -analyzer-checker=security.insecureAPI.mktemp -analyzer-checker=security.insecureAPI.mkstemp -analyzer-checker=security.insecureAPI.vfork -analyzer-checker=nullability.NullPassedToNonnull -analyzer-checker=nullability.NullReturnedFromNonnull -analyzer-output plist -w -setup-static-analyzer -analyzer-config-compatibility-mode=true -mrelocation-model pic -pic-level 2 -mframe-pointer=none -fmath-errno -fno-rounding-math -mconstructor-aliases -munwind-tables -target-cpu x86-64 -tune-cpu generic -debugger-tuning=gdb -ffunction-sections -fdata-sections -fcoverage-compilation-dir=/build/llvm-toolchain-snapshot-14~++20210926122410+d23fd8ae8906/build-llvm -resource-dir /usr/lib/llvm-14/lib/clang/14.0.0 -D _DEBUG -D _GNU_SOURCE -D __STDC_CONSTANT_MACROS -D __STDC_FORMAT_MACROS -D __STDC_LIMIT_MACROS -I lib/Support -I /build/llvm-toolchain-snapshot-14~++20210926122410+d23fd8ae8906/llvm/lib/Support -I include -I /build/llvm-toolchain-snapshot-14~++20210926122410+d23fd8ae8906/llvm/include -D NDEBUG -U NDEBUG -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/10/../../../../include/x86_64-linux-gnu/c++/10 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/backward -internal-isystem /usr/lib/llvm-14/lib/clang/14.0.0/include -internal-isystem /usr/local/include -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/10/../../../../x86_64-linux-gnu/include -internal-externc-isystem /usr/include/x86_64-linux-gnu -internal-externc-isystem /include -internal-externc-isystem /usr/include -O2 -Wno-unused-command-line-argument -Wno-unknown-warning-option -Wno-unused-parameter -Wwrite-strings -Wno-missing-field-initializers -Wno-long-long -Wno-maybe-uninitialized -Wno-class-memaccess -Wno-redundant-move -Wno-pessimizing-move -Wno-noexcept-type -Wno-comment -std=c++14 -fdeprecated-macro -fdebug-compilation-dir=/build/llvm-toolchain-snapshot-14~++20210926122410+d23fd8ae8906/build-llvm -ferror-limit 19 -fvisibility-inlines-hidden -fgnuc-version=4.2.1 -fcolor-diagnostics -vectorize-loops -vectorize-slp -analyzer-output=html -analyzer-config stable-report-filename=true -faddrsig -D__GCC_HAVE_DWARF2_CFI_ASM=1 -o /tmp/scan-build-2021-09-26-234817-15343-1 -x c++ /build/llvm-toolchain-snapshot-14~++20210926122410+d23fd8ae8906/llvm/lib/Support/StringRef.cpp

/build/llvm-toolchain-snapshot-14~++20210926122410+d23fd8ae8906/llvm/lib/Support/StringRef.cpp

1//===-- StringRef.cpp - Lightweight String References ---------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8
9#include "llvm/ADT/StringRef.h"
10#include "llvm/ADT/APFloat.h"
11#include "llvm/ADT/APInt.h"
12#include "llvm/ADT/Hashing.h"
13#include "llvm/ADT/StringExtras.h"
14#include "llvm/ADT/edit_distance.h"
15#include "llvm/Support/Error.h"
16#include <bitset>
17
18using namespace llvm;
19
20// MSVC emits references to this into the translation units which reference it.
21#ifndef _MSC_VER
22constexpr size_t StringRef::npos;
23#endif
24
25// strncasecmp() is not available on non-POSIX systems, so define an
26// alternative function here.
27static int ascii_strncasecmp(const char *LHS, const char *RHS, size_t Length) {
28 for (size_t I = 0; I < Length; ++I) {
29 unsigned char LHC = toLower(LHS[I]);
30 unsigned char RHC = toLower(RHS[I]);
31 if (LHC != RHC)
32 return LHC < RHC ? -1 : 1;
33 }
34 return 0;
35}
36
37int StringRef::compare_insensitive(StringRef RHS) const {
38 if (int Res = ascii_strncasecmp(Data, RHS.Data, std::min(Length, RHS.Length)))
39 return Res;
40 if (Length == RHS.Length)
41 return 0;
42 return Length < RHS.Length ? -1 : 1;
43}
44
45bool StringRef::startswith_insensitive(StringRef Prefix) const {
46 return Length >= Prefix.Length &&
47 ascii_strncasecmp(Data, Prefix.Data, Prefix.Length) == 0;
48}
49
50bool StringRef::endswith_insensitive(StringRef Suffix) const {
51 return Length >= Suffix.Length &&
52 ascii_strncasecmp(end() - Suffix.Length, Suffix.Data, Suffix.Length) == 0;
53}
54
55size_t StringRef::find_insensitive(char C, size_t From) const {
56 char L = toLower(C);
57 return find_if([L](char D) { return toLower(D) == L; }, From);
58}
59
60/// compare_numeric - Compare strings, handle embedded numbers.
61int StringRef::compare_numeric(StringRef RHS) const {
62 for (size_t I = 0, E = std::min(Length, RHS.Length); I != E; ++I) {
63 // Check for sequences of digits.
64 if (isDigit(Data[I]) && isDigit(RHS.Data[I])) {
65 // The longer sequence of numbers is considered larger.
66 // This doesn't really handle prefixed zeros well.
67 size_t J;
68 for (J = I + 1; J != E + 1; ++J) {
69 bool ld = J < Length && isDigit(Data[J]);
70 bool rd = J < RHS.Length && isDigit(RHS.Data[J]);
71 if (ld != rd)
72 return rd ? -1 : 1;
73 if (!rd)
74 break;
75 }
76 // The two number sequences have the same length (J-I), just memcmp them.
77 if (int Res = compareMemory(Data + I, RHS.Data + I, J - I))
78 return Res < 0 ? -1 : 1;
79 // Identical number sequences, continue search after the numbers.
80 I = J - 1;
81 continue;
82 }
83 if (Data[I] != RHS.Data[I])
84 return (unsigned char)Data[I] < (unsigned char)RHS.Data[I] ? -1 : 1;
85 }
86 if (Length == RHS.Length)
87 return 0;
88 return Length < RHS.Length ? -1 : 1;
89}
90
91// Compute the edit distance between the two given strings.
92unsigned StringRef::edit_distance(llvm::StringRef Other,
93 bool AllowReplacements,
94 unsigned MaxEditDistance) const {
95 return llvm::ComputeEditDistance(
1
Calling 'ComputeEditDistance<char>'
96 makeArrayRef(data(), size()),
97 makeArrayRef(Other.data(), Other.size()),
98 AllowReplacements, MaxEditDistance);
99}
100
101//===----------------------------------------------------------------------===//
102// String Operations
103//===----------------------------------------------------------------------===//
104
105std::string StringRef::lower() const {
106 return std::string(map_iterator(begin(), toLower),
107 map_iterator(end(), toLower));
108}
109
110std::string StringRef::upper() const {
111 return std::string(map_iterator(begin(), toUpper),
112 map_iterator(end(), toUpper));
113}
114
115//===----------------------------------------------------------------------===//
116// String Searching
117//===----------------------------------------------------------------------===//
118
119
120/// find - Search for the first string \arg Str in the string.
121///
122/// \return - The index of the first occurrence of \arg Str, or npos if not
123/// found.
124size_t StringRef::find(StringRef Str, size_t From) const {
125 if (From > Length)
126 return npos;
127
128 const char *Start = Data + From;
129 size_t Size = Length - From;
130
131 const char *Needle = Str.data();
132 size_t N = Str.size();
133 if (N == 0)
134 return From;
135 if (Size < N)
136 return npos;
137 if (N == 1) {
138 const char *Ptr = (const char *)::memchr(Start, Needle[0], Size);
139 return Ptr == nullptr ? npos : Ptr - Data;
140 }
141
142 const char *Stop = Start + (Size - N + 1);
143
144 // For short haystacks or unsupported needles fall back to the naive algorithm
145 if (Size < 16 || N > 255) {
146 do {
147 if (std::memcmp(Start, Needle, N) == 0)
148 return Start - Data;
149 ++Start;
150 } while (Start < Stop);
151 return npos;
152 }
153
154 // Build the bad char heuristic table, with uint8_t to reduce cache thrashing.
155 uint8_t BadCharSkip[256];
156 std::memset(BadCharSkip, N, 256);
157 for (unsigned i = 0; i != N-1; ++i)
158 BadCharSkip[(uint8_t)Str[i]] = N-1-i;
159
160 do {
161 uint8_t Last = Start[N - 1];
162 if (LLVM_UNLIKELY(Last == (uint8_t)Needle[N - 1])__builtin_expect((bool)(Last == (uint8_t)Needle[N - 1]), false
)
)
163 if (std::memcmp(Start, Needle, N - 1) == 0)
164 return Start - Data;
165
166 // Otherwise skip the appropriate number of bytes.
167 Start += BadCharSkip[Last];
168 } while (Start < Stop);
169
170 return npos;
171}
172
173size_t StringRef::find_insensitive(StringRef Str, size_t From) const {
174 StringRef This = substr(From);
175 while (This.size() >= Str.size()) {
176 if (This.startswith_insensitive(Str))
177 return From;
178 This = This.drop_front();
179 ++From;
180 }
181 return npos;
182}
183
184size_t StringRef::rfind_insensitive(char C, size_t From) const {
185 From = std::min(From, Length);
186 size_t i = From;
187 while (i != 0) {
188 --i;
189 if (toLower(Data[i]) == toLower(C))
190 return i;
191 }
192 return npos;
193}
194
195/// rfind - Search for the last string \arg Str in the string.
196///
197/// \return - The index of the last occurrence of \arg Str, or npos if not
198/// found.
199size_t StringRef::rfind(StringRef Str) const {
200 size_t N = Str.size();
201 if (N > Length)
202 return npos;
203 for (size_t i = Length - N + 1, e = 0; i != e;) {
204 --i;
205 if (substr(i, N).equals(Str))
206 return i;
207 }
208 return npos;
209}
210
211size_t StringRef::rfind_insensitive(StringRef Str) const {
212 size_t N = Str.size();
213 if (N > Length)
214 return npos;
215 for (size_t i = Length - N + 1, e = 0; i != e;) {
216 --i;
217 if (substr(i, N).equals_insensitive(Str))
218 return i;
219 }
220 return npos;
221}
222
223/// find_first_of - Find the first character in the string that is in \arg
224/// Chars, or npos if not found.
225///
226/// Note: O(size() + Chars.size())
227StringRef::size_type StringRef::find_first_of(StringRef Chars,
228 size_t From) const {
229 std::bitset<1 << CHAR_BIT8> CharBits;
230 for (size_type i = 0; i != Chars.size(); ++i)
231 CharBits.set((unsigned char)Chars[i]);
232
233 for (size_type i = std::min(From, Length), e = Length; i != e; ++i)
234 if (CharBits.test((unsigned char)Data[i]))
235 return i;
236 return npos;
237}
238
239/// find_first_not_of - Find the first character in the string that is not
240/// \arg C or npos if not found.
241StringRef::size_type StringRef::find_first_not_of(char C, size_t From) const {
242 for (size_type i = std::min(From, Length), e = Length; i != e; ++i)
243 if (Data[i] != C)
244 return i;
245 return npos;
246}
247
248/// find_first_not_of - Find the first character in the string that is not
249/// in the string \arg Chars, or npos if not found.
250///
251/// Note: O(size() + Chars.size())
252StringRef::size_type StringRef::find_first_not_of(StringRef Chars,
253 size_t From) const {
254 std::bitset<1 << CHAR_BIT8> CharBits;
255 for (size_type i = 0; i != Chars.size(); ++i)
256 CharBits.set((unsigned char)Chars[i]);
257
258 for (size_type i = std::min(From, Length), e = Length; i != e; ++i)
259 if (!CharBits.test((unsigned char)Data[i]))
260 return i;
261 return npos;
262}
263
264/// find_last_of - Find the last character in the string that is in \arg C,
265/// or npos if not found.
266///
267/// Note: O(size() + Chars.size())
268StringRef::size_type StringRef::find_last_of(StringRef Chars,
269 size_t From) const {
270 std::bitset<1 << CHAR_BIT8> CharBits;
271 for (size_type i = 0; i != Chars.size(); ++i)
272 CharBits.set((unsigned char)Chars[i]);
273
274 for (size_type i = std::min(From, Length) - 1, e = -1; i != e; --i)
275 if (CharBits.test((unsigned char)Data[i]))
276 return i;
277 return npos;
278}
279
280/// find_last_not_of - Find the last character in the string that is not
281/// \arg C, or npos if not found.
282StringRef::size_type StringRef::find_last_not_of(char C, size_t From) const {
283 for (size_type i = std::min(From, Length) - 1, e = -1; i != e; --i)
284 if (Data[i] != C)
285 return i;
286 return npos;
287}
288
289/// find_last_not_of - Find the last character in the string that is not in
290/// \arg Chars, or npos if not found.
291///
292/// Note: O(size() + Chars.size())
293StringRef::size_type StringRef::find_last_not_of(StringRef Chars,
294 size_t From) const {
295 std::bitset<1 << CHAR_BIT8> CharBits;
296 for (size_type i = 0, e = Chars.size(); i != e; ++i)
297 CharBits.set((unsigned char)Chars[i]);
298
299 for (size_type i = std::min(From, Length) - 1, e = -1; i != e; --i)
300 if (!CharBits.test((unsigned char)Data[i]))
301 return i;
302 return npos;
303}
304
305void StringRef::split(SmallVectorImpl<StringRef> &A,
306 StringRef Separator, int MaxSplit,
307 bool KeepEmpty) const {
308 StringRef S = *this;
309
310 // Count down from MaxSplit. When MaxSplit is -1, this will just split
311 // "forever". This doesn't support splitting more than 2^31 times
312 // intentionally; if we ever want that we can make MaxSplit a 64-bit integer
313 // but that seems unlikely to be useful.
314 while (MaxSplit-- != 0) {
315 size_t Idx = S.find(Separator);
316 if (Idx == npos)
317 break;
318
319 // Push this split.
320 if (KeepEmpty || Idx > 0)
321 A.push_back(S.slice(0, Idx));
322
323 // Jump forward.
324 S = S.slice(Idx + Separator.size(), npos);
325 }
326
327 // Push the tail.
328 if (KeepEmpty || !S.empty())
329 A.push_back(S);
330}
331
332void StringRef::split(SmallVectorImpl<StringRef> &A, char Separator,
333 int MaxSplit, bool KeepEmpty) const {
334 StringRef S = *this;
335
336 // Count down from MaxSplit. When MaxSplit is -1, this will just split
337 // "forever". This doesn't support splitting more than 2^31 times
338 // intentionally; if we ever want that we can make MaxSplit a 64-bit integer
339 // but that seems unlikely to be useful.
340 while (MaxSplit-- != 0) {
341 size_t Idx = S.find(Separator);
342 if (Idx == npos)
343 break;
344
345 // Push this split.
346 if (KeepEmpty || Idx > 0)
347 A.push_back(S.slice(0, Idx));
348
349 // Jump forward.
350 S = S.slice(Idx + 1, npos);
351 }
352
353 // Push the tail.
354 if (KeepEmpty || !S.empty())
355 A.push_back(S);
356}
357
358//===----------------------------------------------------------------------===//
359// Helpful Algorithms
360//===----------------------------------------------------------------------===//
361
362/// count - Return the number of non-overlapped occurrences of \arg Str in
363/// the string.
364size_t StringRef::count(StringRef Str) const {
365 size_t Count = 0;
366 size_t N = Str.size();
367 if (!N || N > Length)
368 return 0;
369 for (size_t i = 0, e = Length - N + 1; i < e;) {
370 if (substr(i, N).equals(Str)) {
371 ++Count;
372 i += N;
373 }
374 else
375 ++i;
376 }
377 return Count;
378}
379
380static unsigned GetAutoSenseRadix(StringRef &Str) {
381 if (Str.empty())
382 return 10;
383
384 if (Str.startswith("0x") || Str.startswith("0X")) {
385 Str = Str.substr(2);
386 return 16;
387 }
388
389 if (Str.startswith("0b") || Str.startswith("0B")) {
390 Str = Str.substr(2);
391 return 2;
392 }
393
394 if (Str.startswith("0o")) {
395 Str = Str.substr(2);
396 return 8;
397 }
398
399 if (Str[0] == '0' && Str.size() > 1 && isDigit(Str[1])) {
400 Str = Str.substr(1);
401 return 8;
402 }
403
404 return 10;
405}
406
407bool llvm::consumeUnsignedInteger(StringRef &Str, unsigned Radix,
408 unsigned long long &Result) {
409 // Autosense radix if not specified.
410 if (Radix == 0)
411 Radix = GetAutoSenseRadix(Str);
412
413 // Empty strings (after the radix autosense) are invalid.
414 if (Str.empty()) return true;
415
416 // Parse all the bytes of the string given this radix. Watch for overflow.
417 StringRef Str2 = Str;
418 Result = 0;
419 while (!Str2.empty()) {
420 unsigned CharVal;
421 if (Str2[0] >= '0' && Str2[0] <= '9')
422 CharVal = Str2[0] - '0';
423 else if (Str2[0] >= 'a' && Str2[0] <= 'z')
424 CharVal = Str2[0] - 'a' + 10;
425 else if (Str2[0] >= 'A' && Str2[0] <= 'Z')
426 CharVal = Str2[0] - 'A' + 10;
427 else
428 break;
429
430 // If the parsed value is larger than the integer radix, we cannot
431 // consume any more characters.
432 if (CharVal >= Radix)
433 break;
434
435 // Add in this character.
436 unsigned long long PrevResult = Result;
437 Result = Result * Radix + CharVal;
438
439 // Check for overflow by shifting back and seeing if bits were lost.
440 if (Result / Radix < PrevResult)
441 return true;
442
443 Str2 = Str2.substr(1);
444 }
445
446 // We consider the operation a failure if no characters were consumed
447 // successfully.
448 if (Str.size() == Str2.size())
449 return true;
450
451 Str = Str2;
452 return false;
453}
454
455bool llvm::consumeSignedInteger(StringRef &Str, unsigned Radix,
456 long long &Result) {
457 unsigned long long ULLVal;
458
459 // Handle positive strings first.
460 if (Str.empty() || Str.front() != '-') {
461 if (consumeUnsignedInteger(Str, Radix, ULLVal) ||
462 // Check for value so large it overflows a signed value.
463 (long long)ULLVal < 0)
464 return true;
465 Result = ULLVal;
466 return false;
467 }
468
469 // Get the positive part of the value.
470 StringRef Str2 = Str.drop_front(1);
471 if (consumeUnsignedInteger(Str2, Radix, ULLVal) ||
472 // Reject values so large they'd overflow as negative signed, but allow
473 // "-0". This negates the unsigned so that the negative isn't undefined
474 // on signed overflow.
475 (long long)-ULLVal > 0)
476 return true;
477
478 Str = Str2;
479 Result = -ULLVal;
480 return false;
481}
482
483/// GetAsUnsignedInteger - Workhorse method that converts a integer character
484/// sequence of radix up to 36 to an unsigned long long value.
485bool llvm::getAsUnsignedInteger(StringRef Str, unsigned Radix,
486 unsigned long long &Result) {
487 if (consumeUnsignedInteger(Str, Radix, Result))
488 return true;
489
490 // For getAsUnsignedInteger, we require the whole string to be consumed or
491 // else we consider it a failure.
492 return !Str.empty();
493}
494
495bool llvm::getAsSignedInteger(StringRef Str, unsigned Radix,
496 long long &Result) {
497 if (consumeSignedInteger(Str, Radix, Result))
498 return true;
499
500 // For getAsSignedInteger, we require the whole string to be consumed or else
501 // we consider it a failure.
502 return !Str.empty();
503}
504
505bool StringRef::getAsInteger(unsigned Radix, APInt &Result) const {
506 StringRef Str = *this;
507
508 // Autosense radix if not specified.
509 if (Radix == 0)
510 Radix = GetAutoSenseRadix(Str);
511
512 assert(Radix > 1 && Radix <= 36)(static_cast <bool> (Radix > 1 && Radix <=
36) ? void (0) : __assert_fail ("Radix > 1 && Radix <= 36"
, "/build/llvm-toolchain-snapshot-14~++20210926122410+d23fd8ae8906/llvm/lib/Support/StringRef.cpp"
, 512, __extension__ __PRETTY_FUNCTION__))
;
513
514 // Empty strings (after the radix autosense) are invalid.
515 if (Str.empty()) return true;
516
517 // Skip leading zeroes. This can be a significant improvement if
518 // it means we don't need > 64 bits.
519 while (!Str.empty() && Str.front() == '0')
520 Str = Str.substr(1);
521
522 // If it was nothing but zeroes....
523 if (Str.empty()) {
524 Result = APInt(64, 0);
525 return false;
526 }
527
528 // (Over-)estimate the required number of bits.
529 unsigned Log2Radix = 0;
530 while ((1U << Log2Radix) < Radix) Log2Radix++;
531 bool IsPowerOf2Radix = ((1U << Log2Radix) == Radix);
532
533 unsigned BitWidth = Log2Radix * Str.size();
534 if (BitWidth < Result.getBitWidth())
535 BitWidth = Result.getBitWidth(); // don't shrink the result
536 else if (BitWidth > Result.getBitWidth())
537 Result = Result.zext(BitWidth);
538
539 APInt RadixAP, CharAP; // unused unless !IsPowerOf2Radix
540 if (!IsPowerOf2Radix) {
541 // These must have the same bit-width as Result.
542 RadixAP = APInt(BitWidth, Radix);
543 CharAP = APInt(BitWidth, 0);
544 }
545
546 // Parse all the bytes of the string given this radix.
547 Result = 0;
548 while (!Str.empty()) {
549 unsigned CharVal;
550 if (Str[0] >= '0' && Str[0] <= '9')
551 CharVal = Str[0]-'0';
552 else if (Str[0] >= 'a' && Str[0] <= 'z')
553 CharVal = Str[0]-'a'+10;
554 else if (Str[0] >= 'A' && Str[0] <= 'Z')
555 CharVal = Str[0]-'A'+10;
556 else
557 return true;
558
559 // If the parsed value is larger than the integer radix, the string is
560 // invalid.
561 if (CharVal >= Radix)
562 return true;
563
564 // Add in this character.
565 if (IsPowerOf2Radix) {
566 Result <<= Log2Radix;
567 Result |= CharVal;
568 } else {
569 Result *= RadixAP;
570 CharAP = CharVal;
571 Result += CharAP;
572 }
573
574 Str = Str.substr(1);
575 }
576
577 return false;
578}
579
580bool StringRef::getAsDouble(double &Result, bool AllowInexact) const {
581 APFloat F(0.0);
582 auto StatusOrErr = F.convertFromString(*this, APFloat::rmNearestTiesToEven);
583 if (errorToBool(StatusOrErr.takeError()))
584 return true;
585
586 APFloat::opStatus Status = *StatusOrErr;
587 if (Status != APFloat::opOK) {
588 if (!AllowInexact || !(Status & APFloat::opInexact))
589 return true;
590 }
591
592 Result = F.convertToDouble();
593 return false;
594}
595
596// Implementation of StringRef hashing.
597hash_code llvm::hash_value(StringRef S) {
598 return hash_combine_range(S.begin(), S.end());
599}

/build/llvm-toolchain-snapshot-14~++20210926122410+d23fd8ae8906/llvm/include/llvm/ADT/edit_distance.h

1//===-- llvm/ADT/edit_distance.h - Array edit distance function --- C++ -*-===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This file defines a Levenshtein distance function that works for any two
10// sequences, with each element of each sequence being analogous to a character
11// in a string.
12//
13//===----------------------------------------------------------------------===//
14
15#ifndef LLVM_ADT_EDIT_DISTANCE_H
16#define LLVM_ADT_EDIT_DISTANCE_H
17
18#include "llvm/ADT/ArrayRef.h"
19#include <algorithm>
20#include <memory>
21
22namespace llvm {
23
24/// Determine the edit distance between two sequences.
25///
26/// \param FromArray the first sequence to compare.
27///
28/// \param ToArray the second sequence to compare.
29///
30/// \param AllowReplacements whether to allow element replacements (change one
31/// element into another) as a single operation, rather than as two operations
32/// (an insertion and a removal).
33///
34/// \param MaxEditDistance If non-zero, the maximum edit distance that this
35/// routine is allowed to compute. If the edit distance will exceed that
36/// maximum, returns \c MaxEditDistance+1.
37///
38/// \returns the minimum number of element insertions, removals, or (if
39/// \p AllowReplacements is \c true) replacements needed to transform one of
40/// the given sequences into the other. If zero, the sequences are identical.
41template<typename T>
42unsigned ComputeEditDistance(ArrayRef<T> FromArray, ArrayRef<T> ToArray,
43 bool AllowReplacements = true,
44 unsigned MaxEditDistance = 0) {
45 // The algorithm implemented below is the "classic"
46 // dynamic-programming algorithm for computing the Levenshtein
47 // distance, which is described here:
48 //
49 // http://en.wikipedia.org/wiki/Levenshtein_distance
50 //
51 // Although the algorithm is typically described using an m x n
52 // array, only one row plus one element are used at a time, so this
53 // implementation just keeps one vector for the row. To update one entry,
54 // only the entries to the left, top, and top-left are needed. The left
55 // entry is in Row[x-1], the top entry is what's in Row[x] from the last
56 // iteration, and the top-left entry is stored in Previous.
57 typename ArrayRef<T>::size_type m = FromArray.size();
58 typename ArrayRef<T>::size_type n = ToArray.size();
2
'n' initialized here
59
60 const unsigned SmallBufferSize = 64;
61 unsigned SmallBuffer[SmallBufferSize];
62 std::unique_ptr<unsigned[]> Allocated;
63 unsigned *Row = SmallBuffer;
64 if (n + 1 > SmallBufferSize) {
3
Assuming the condition is false
4
Taking false branch
65 Row = new unsigned[n + 1];
66 Allocated.reset(Row);
67 }
68
69 for (unsigned i = 1; i <= n; ++i)
5
Assuming 'i' is > 'n'
6
Loop condition is false. Execution continues on line 72
70 Row[i] = i;
71
72 for (typename ArrayRef<T>::size_type y = 1; y <= m; ++y) {
7
Assuming 'y' is > 'm'
8
Loop condition is false. Execution continues on line 96
73 Row[0] = y;
74 unsigned BestThisRow = Row[0];
75
76 unsigned Previous = y - 1;
77 for (typename ArrayRef<T>::size_type x = 1; x <= n; ++x) {
78 int OldRow = Row[x];
79 if (AllowReplacements) {
80 Row[x] = std::min(
81 Previous + (FromArray[y-1] == ToArray[x-1] ? 0u : 1u),
82 std::min(Row[x-1], Row[x])+1);
83 }
84 else {
85 if (FromArray[y-1] == ToArray[x-1]) Row[x] = Previous;
86 else Row[x] = std::min(Row[x-1], Row[x]) + 1;
87 }
88 Previous = OldRow;
89 BestThisRow = std::min(BestThisRow, Row[x]);
90 }
91
92 if (MaxEditDistance && BestThisRow > MaxEditDistance)
93 return MaxEditDistance + 1;
94 }
95
96 unsigned Result = Row[n];
9
Assigned value is garbage or undefined
97 return Result;
98}
99
100} // End llvm namespace
101
102#endif