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Further optimize performance of terminal output

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Profiling shows that parsing color names still took much longer than it
should.

wcscasecmp is so slow that using it directly causes `try_parse_special`
to consume up to 3% of all of fish's cpu time due to extremely
inefficient invariant case lookups for wide characters (tested: Fedora
Server 32 w/ glibc 2.31 with -O2).
This commit is contained in:
Mahmoud Al-Qudsi 2020-06-22 23:35:23 -05:00
parent c7a8e35bfc
commit 8b910d6de2
1 changed files with 19 additions and 6 deletions
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25
src/color.cpp
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@ -16,12 +16,25 @@
bool rgb_color_t::try_parse_special(const wcstring &special) {
std::memset(&data, 0, sizeof data);
const wchar_t *name = special.c_str();
if (!wcscasecmp(name, L"normal")) {
this->type = type_normal;
} else if (!wcscasecmp(name, L"reset")) {
this->type = type_reset;
} else {
this->type = type_none;
// wcscasecmp is so slow that using it directly causes `try_parse_special` to consume up to
// 3% of all of fish's cpu time due to extremely inefficient invariant case lookups for wide
// characters (tested: Fedora Server 32 w/ glibc 2.31 with -O2). (This function is also called
// virtually non-stop while emitting output to determine colorization.)
// Take advantage of the fact that std::string length is O(1) to speed things up, and perform
// what amounts to a simple memcmp before needing to access the invariant case lookup tables.
static auto normal_len = wcslen(L"normal");
static auto reset_len = wcslen(L"reset");
this->type = type_none;
if (special.size() == normal_len) {
if (!wcscmp(name, L"normal") || !wcscasecmp(name, L"normal")) {
this->type = type_normal;
}
} else if (special.size() == reset_len) {
if (!wcscmp(name, L"reset") || !wcscasecmp(name, L"reset")) {
this->type = type_reset;
}
}
return this->type != type_none;
}