llvm-6502/lib/Support/StringRef.cpp
Douglas Gregor 7e54d5b156 Document the edit-distance algorithm used in StringRef, switch it over
to SmallVector, and add a unit test.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@92340 91177308-0d34-0410-b5e6-96231b3b80d8
2009-12-31 04:24:34 +00:00

264 lines
7.6 KiB
C++

//===-- StringRef.cpp - Lightweight String References ---------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#include "llvm/ADT/StringRef.h"
#include "llvm/ADT/SmallVector.h"
using namespace llvm;
// MSVC emits references to this into the translation units which reference it.
#ifndef _MSC_VER
const size_t StringRef::npos;
#endif
static char ascii_tolower(char x) {
if (x >= 'A' && x <= 'Z')
return x - 'A' + 'a';
return x;
}
/// compare_lower - Compare strings, ignoring case.
int StringRef::compare_lower(StringRef RHS) const {
for (size_t I = 0, E = min(Length, RHS.Length); I != E; ++I) {
char LHC = ascii_tolower(Data[I]);
char RHC = ascii_tolower(RHS.Data[I]);
if (LHC != RHC)
return LHC < RHC ? -1 : 1;
}
if (Length == RHS.Length)
return 0;
return Length < RHS.Length ? -1 : 1;
}
// Compute the edit distance between the two given strings.
unsigned StringRef::edit_distance(llvm::StringRef Other,
bool AllowReplacements) {
// The algorithm implemented below is the "classic"
// dynamic-programming algorithm for computing the Levenshtein
// distance, which is described here:
//
// http://en.wikipedia.org/wiki/Levenshtein_distance
//
// Although the algorithm is typically described using an m x n
// array, only two rows are used at a time, so this implemenation
// just keeps two separate vectors for those two rows.
size_type m = size();
size_type n = Other.size();
SmallVector<unsigned, 32> previous(n+1, 0);
for (SmallVector<unsigned, 32>::size_type i = 0; i <= n; ++i)
previous[i] = i;
SmallVector<unsigned, 32> current(n+1, 0);
for (size_type y = 1; y <= m; ++y) {
current.assign(n+1, 0);
current[0] = y;
for (size_type x = 1; x <= n; ++x) {
if (AllowReplacements) {
current[x] = min(previous[x-1] + ((*this)[y-1] == Other[x-1]? 0u:1u),
min(current[x-1], previous[x])+1);
}
else {
if ((*this)[y-1] == Other[x-1]) current[x] = previous[x-1];
else current[x] = min(current[x-1], previous[x]) + 1;
}
}
current.swap(previous);
}
return previous[n];
}
//===----------------------------------------------------------------------===//
// String Searching
//===----------------------------------------------------------------------===//
/// find - Search for the first string \arg Str in the string.
///
/// \return - The index of the first occurence of \arg Str, or npos if not
/// found.
size_t StringRef::find(StringRef Str, size_t From) const {
size_t N = Str.size();
if (N > Length)
return npos;
for (size_t e = Length - N + 1, i = min(From, e); i != e; ++i)
if (substr(i, N).equals(Str))
return i;
return npos;
}
/// rfind - Search for the last string \arg Str in the string.
///
/// \return - The index of the last occurence of \arg Str, or npos if not
/// found.
size_t StringRef::rfind(StringRef Str) const {
size_t N = Str.size();
if (N > Length)
return npos;
for (size_t i = Length - N + 1, e = 0; i != e;) {
--i;
if (substr(i, N).equals(Str))
return i;
}
return npos;
}
/// find_first_of - Find the first character in the string that is in \arg
/// Chars, or npos if not found.
///
/// Note: O(size() * Chars.size())
StringRef::size_type StringRef::find_first_of(StringRef Chars,
size_t From) const {
for (size_type i = min(From, Length), e = Length; i != e; ++i)
if (Chars.find(Data[i]) != npos)
return i;
return npos;
}
/// find_first_not_of - Find the first character in the string that is not
/// \arg C or npos if not found.
StringRef::size_type StringRef::find_first_not_of(char C, size_t From) const {
for (size_type i = min(From, Length), e = Length; i != e; ++i)
if (Data[i] != C)
return i;
return npos;
}
/// find_first_not_of - Find the first character in the string that is not
/// in the string \arg Chars, or npos if not found.
///
/// Note: O(size() * Chars.size())
StringRef::size_type StringRef::find_first_not_of(StringRef Chars,
size_t From) const {
for (size_type i = min(From, Length), e = Length; i != e; ++i)
if (Chars.find(Data[i]) == npos)
return i;
return npos;
}
//===----------------------------------------------------------------------===//
// Helpful Algorithms
//===----------------------------------------------------------------------===//
/// count - Return the number of non-overlapped occurrences of \arg Str in
/// the string.
size_t StringRef::count(StringRef Str) const {
size_t Count = 0;
size_t N = Str.size();
if (N > Length)
return 0;
for (size_t i = 0, e = Length - N + 1; i != e; ++i)
if (substr(i, N).equals(Str))
++Count;
return Count;
}
/// GetAsUnsignedInteger - Workhorse method that converts a integer character
/// sequence of radix up to 36 to an unsigned long long value.
static bool GetAsUnsignedInteger(StringRef Str, unsigned Radix,
unsigned long long &Result) {
// Autosense radix if not specified.
if (Radix == 0) {
if (Str.startswith("0x")) {
Str = Str.substr(2);
Radix = 16;
} else if (Str.startswith("0b")) {
Str = Str.substr(2);
Radix = 2;
} else if (Str.startswith("0"))
Radix = 8;
else
Radix = 10;
}
// Empty strings (after the radix autosense) are invalid.
if (Str.empty()) return true;
// Parse all the bytes of the string given this radix. Watch for overflow.
Result = 0;
while (!Str.empty()) {
unsigned CharVal;
if (Str[0] >= '0' && Str[0] <= '9')
CharVal = Str[0]-'0';
else if (Str[0] >= 'a' && Str[0] <= 'z')
CharVal = Str[0]-'a'+10;
else if (Str[0] >= 'A' && Str[0] <= 'Z')
CharVal = Str[0]-'A'+10;
else
return true;
// If the parsed value is larger than the integer radix, the string is
// invalid.
if (CharVal >= Radix)
return true;
// Add in this character.
unsigned long long PrevResult = Result;
Result = Result*Radix+CharVal;
// Check for overflow.
if (Result < PrevResult)
return true;
Str = Str.substr(1);
}
return false;
}
bool StringRef::getAsInteger(unsigned Radix, unsigned long long &Result) const {
return GetAsUnsignedInteger(*this, Radix, Result);
}
bool StringRef::getAsInteger(unsigned Radix, long long &Result) const {
unsigned long long ULLVal;
// Handle positive strings first.
if (empty() || front() != '-') {
if (GetAsUnsignedInteger(*this, Radix, ULLVal) ||
// Check for value so large it overflows a signed value.
(long long)ULLVal < 0)
return true;
Result = ULLVal;
return false;
}
// Get the positive part of the value.
if (GetAsUnsignedInteger(substr(1), Radix, ULLVal) ||
// Reject values so large they'd overflow as negative signed, but allow
// "-0". This negates the unsigned so that the negative isn't undefined
// on signed overflow.
(long long)-ULLVal > 0)
return true;
Result = -ULLVal;
return false;
}
bool StringRef::getAsInteger(unsigned Radix, int &Result) const {
long long Val;
if (getAsInteger(Radix, Val) ||
(int)Val != Val)
return true;
Result = Val;
return false;
}
bool StringRef::getAsInteger(unsigned Radix, unsigned &Result) const {
unsigned long long Val;
if (getAsInteger(Radix, Val) ||
(unsigned)Val != Val)
return true;
Result = Val;
return false;
}