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Changed Boyer-Moore's bad-char table code:

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- Reduce it to half size if the pattern is ASCII, saving on initialization
- If pattern is ASCII and subject is not, any non-ASCII char can cause a
  full pattern-length shift, even if we haven't indexed the entire pattern.
- Use memset to initialize buffer in the common case where the pattern is
  shorter than the max significant suffix limit.


git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@519 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
This commit is contained in:
lrn@chromium.org 2008-10-17 11:15:54 +00:00
parent ebd11b7382
commit dc87d51f70
1 changed files with 27 additions and 8 deletions
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35
src/runtime.cc
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@ -965,7 +965,7 @@ static const int kBMMinPatternLength = 5;
// Holds the two buffers used by Boyer-Moore string search's Good Suffix
// shift. Only allows the last kBMMaxShift characters of the needle
// to be indexed.
class BMGoodSuffixBuffers: public AllStatic {
class BMGoodSuffixBuffers {
public:
BMGoodSuffixBuffers() {}
inline void init(int needle_length) {
@ -1005,12 +1005,18 @@ static void BoyerMoorePopulateBadCharTable(Vector<const pchar> pattern,
// Run forwards to populate bad_char_table, so that *last* instance
// of character equivalence class is the one registered.
// Notice: Doesn't include the last character.
for (int i = 0; i < kBMAlphabetSize; i++) {
bad_char_occurence[i] = start - 1;
int table_size = (sizeof(pchar) == 1) ? String::kMaxAsciiCharCode + 1
: kBMAlphabetSize;
if (start == 0) { // All patterns less than kBMMaxShift in length.
memset(bad_char_occurence, -1, table_size * sizeof(*bad_char_occurence));
} else {
for (int i = 0; i < table_size; i++) {
bad_char_occurence[i] = start - 1;
}
}
for (int i = start; i < pattern.length() - 1; i++) {
pchar c = pattern[i];
int bucket = c % kBMAlphabetSize;
int bucket = (sizeof(pchar) ==1) ? c : c % kBMAlphabetSize;
bad_char_occurence[bucket] = i;
}
}
@ -1065,6 +1071,19 @@ static void BoyerMoorePopulateGoodSuffixTable(Vector<const pchar> pattern,
}
}
template <typename schar, typename pchar>
static inline int CharOccurence(int char_code) {
if (sizeof(schar) == 1) {
return bad_char_occurence[char_code];
}
if (sizeof(pchar) == 1) {
if (char_code > String::kMaxAsciiCharCode) {
return -1;
}
return bad_char_occurence[char_code];
}
return bad_char_occurence[char_code % kBMAlphabetSize];
}
// Restricted simplified Boyer-Moore string matching. Restricts tables to a
// suffix of long pattern strings and handles only equivalence classes
@ -1090,7 +1109,7 @@ static int BoyerMooreSimplified(Vector<const schar> subject,
int j = m - 1;
int c;
while (last_char != (c = subject[idx + j])) {
int bc_occ = bad_char_occurence[c % kBMAlphabetSize];
int bc_occ = CharOccurence<schar, pchar>(c);
int shift = j - bc_occ;
idx += shift;
badness += 1 - shift; // at most zero, so badness cannot increase.
@ -1105,7 +1124,7 @@ static int BoyerMooreSimplified(Vector<const schar> subject,
complete = true;
return idx;
} else {
int bc_occ = bad_char_occurence[c % kBMAlphabetSize];
int bc_occ = CharOccurence<schar, pchar>(c);
int shift = bc_occ < j ? j - bc_occ : 1;
idx += shift;
// Badness increases by the number of characters we have
@ -1141,7 +1160,7 @@ static int BoyerMooreIndexOf(Vector<const schar> subject,
int j = m - 1;
schar c;
while (last_char != (c = subject[idx + j])) {
int shift = j - bad_char_occurence[c % kBMAlphabetSize];
int shift = j - CharOccurence<schar, pchar>(c);
idx += shift;
if (idx > n - m) {
return -1;
@ -1155,7 +1174,7 @@ static int BoyerMooreIndexOf(Vector<const schar> subject,
idx += 1;
} else {
int gs_shift = bmgs_buffers.shift(j + 1); // Good suffix shift.
int bc_occ = bad_char_occurence[c % kBMAlphabetSize];
int bc_occ = CharOccurence<schar, pchar>(c);
int shift = j - bc_occ; // Bad-char shift.
shift = (gs_shift > shift) ? gs_shift : shift;
idx += shift;