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closes #425: faster ToLowerCase() with ideas from M1383647

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This commit is contained in:
Cameron Kaiser 2017-12-14 09:42:58 -08:00
parent 71abc4edc1
commit bfaa83964f
1 changed files with 64 additions and 6 deletions
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70
js/src/jsstr.cpp
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@ -606,6 +606,64 @@ js::SubstringKernel(JSContext* cx, HandleString str, int32_t beginInt, int32_t l
return NewDependentString(cx, str, begin, len);
}
// Adapted from bug 1383647
static inline bool
FastLatin1LowerCase(Latin1Char ch)
{
if (MOZ_LIKELY(ch < 128))
return ch >= 'A' && ch <= 'Z';
// U+00C0 to U+00DE, except U+00D7, have a lowercase form.
bool canLower = ((ch & ~0x1F) == /* LATIN_CAPITAL_LETTER_A_WITH_GRAVE */ 0xc0) &&
((ch & /* MULTIPLICATION_SIGN */ 0xd7) != 0xd7);
MOZ_ASSERT(canLower == CanLowerCase(char16_t(ch)));
return canLower;
}
static JSString*
ToLowerCaseLatin1(JSContext* cx, JSLinearString* str)
{
// Unlike toUpperCase, toLowerCase has the nice invariant that if the input
// is a Latin1 string, the output is also a Latin1 string.
UniquePtr<Latin1Char[], JS::FreePolicy> newChars;
size_t length = str->length();
{
AutoCheckCannotGC nogc;
const Latin1Char* chars = str->chars<Latin1Char>(nogc);
// Look for the first upper case character.
size_t i = 0;
for (; i < length; i++) {
if (FastLatin1LowerCase(chars[i]))
break;
}
// If all characters are lower case, return the input string.
if (i == length)
return str;
newChars = cx->make_pod_array<Latin1Char>(length + 1);
if (MOZ_UNLIKELY(!newChars))
return nullptr;
PodCopy(newChars.get(), chars, i);
for (; i < length; i++) {
char16_t c = unicode::ToLowerCase(chars[i]);
MOZ_ASSERT_IF((IsSame<Latin1Char, Latin1Char>::value), c <= JSString::MAX_LATIN1_CHAR);
newChars[i] = c;
}
newChars[length] = 0;
}
JSString* res = NewStringDontDeflate<CanGC>(cx, newChars.get(), length);
if (MOZ_UNLIKELY(!res))
return nullptr;
newChars.release();
return res;
}
template <typename CharT>
static JSString*
ToLowerCase(JSContext* cx, JSLinearString* str)
@ -631,7 +689,7 @@ ToLowerCase(JSContext* cx, JSLinearString* str)
return str;
newChars = cx->make_pod_array<CharT>(length + 1);
if (!newChars)
if (MOZ_UNLIKELY(!newChars))
return nullptr;
PodCopy(newChars.get(), chars, i);
@ -646,7 +704,7 @@ ToLowerCase(JSContext* cx, JSLinearString* str)
}
JSString* res = NewStringDontDeflate<CanGC>(cx, newChars.get(), length);
if (!res)
if (MOZ_UNLIKELY(!res))
return nullptr;
newChars.release();
@ -657,18 +715,18 @@ static inline bool
ToLowerCaseHelper(JSContext* cx, CallReceiver call)
{
RootedString str(cx, ThisToStringForStringProto(cx, call));
if (!str)
if (MOZ_UNLIKELY(!str))
return false;
JSLinearString* linear = str->ensureLinear(cx);
if (!linear)
if (MOZ_UNLIKELY(!linear))
return false;
if (linear->hasLatin1Chars())
str = ToLowerCase<Latin1Char>(cx, linear);
str = ToLowerCaseLatin1(cx, linear);
else
str = ToLowerCase<char16_t>(cx, linear);
if (!str)
if (MOZ_UNLIKELY(!str))
return false;
call.rval().setString(str);