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LibJS: Add a non-BigInt overload of GetNamedTimeZoneOffsetNanoseconds

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In some cases, we have a timestamp as a double in milliseconds. We then
would convert it to nanoseconds as a BigInt, just to bring it back to a
double for TZDB lookups. Add an overload to avoid this needless round
trip.
This commit is contained in:
Timothy Flynn 2024-09-03 10:26:03 -04:00 committed by Andreas Kling
parent 5ee92af1d9
commit 6becd13a83
Notes: github-actions[bot] 2024-09-03 17:27:01 +00:00 
Author: https://github.com/trflynn89
Commit: https://github.com/LadybirdBrowser/ladybird/commit/6becd13a83a
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/1266
3 changed files with 32 additions and 4 deletions
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32
Userland/Libraries/LibJS/Runtime/Date.cpp
View file

@ -382,6 +382,22 @@ static i64 clip_bigint_to_sane_time(Crypto::SignedBigInteger const& value)
return value.to_base_deprecated(10).to_number<i64>().value();
}
static i64 clip_double_to_sane_time(double value)
{
static constexpr auto min_double = static_cast<double>(NumericLimits<i64>::min());
static constexpr auto max_double = static_cast<double>(NumericLimits<i64>::max());
// The provided epoch millseconds value is potentially out of range for AK::Duration and subsequently
// get_time_zone_offset(). We can safely assume that the TZDB has no useful information that far
// into the past and future anyway, so clamp it to the i64 range.
if (value < min_double)
return NumericLimits<i64>::min();
if (value > max_double)
return NumericLimits<i64>::max();
return static_cast<i64>(value);
}
// 21.4.1.20 GetNamedTimeZoneEpochNanoseconds ( timeZoneIdentifier, year, month, day, hour, minute, second, millisecond, microsecond, nanosecond ), https://tc39.es/ecma262/#sec-getnamedtimezoneepochnanoseconds
Vector<Crypto::SignedBigInteger> get_named_time_zone_epoch_nanoseconds(StringView time_zone_identifier, i32 year, u8 month, u8 day, u8 hour, u8 minute, u8 second, u16 millisecond, u16 microsecond, u16 nanosecond)
{
@ -411,6 +427,19 @@ Unicode::TimeZoneOffset get_named_time_zone_offset_nanoseconds(StringView time_z
return offset.release_value();
}
// 21.4.1.21 GetNamedTimeZoneOffsetNanoseconds ( timeZoneIdentifier, epochNanoseconds ), https://tc39.es/ecma262/#sec-getnamedtimezoneoffsetnanoseconds
// OPTIMIZATION: This overload is provided to allow callers to avoid BigInt construction if they do not need infinitely precise nanosecond resolution.
Unicode::TimeZoneOffset get_named_time_zone_offset_milliseconds(StringView time_zone_identifier, double epoch_milliseconds)
{
auto seconds = epoch_milliseconds / 1000.0;
auto time = UnixDateTime::from_seconds_since_epoch(clip_double_to_sane_time(seconds));
auto offset = Unicode::time_zone_offset(time_zone_identifier, time);
VERIFY(offset.has_value());
return offset.release_value();
}
static Optional<String> cached_system_time_zone_identifier;
// 21.4.1.24 SystemTimeZoneIdentifier ( ), https://tc39.es/ecma262/#sec-systemtimezoneidentifier
@ -460,8 +489,7 @@ double local_time(double time)
// 3. Else,
else {
// a. Let offsetNs be GetNamedTimeZoneOffsetNanoseconds(systemTimeZoneIdentifier, ℤ(ℝ(t) × 10^6)).
auto time_bigint = Crypto::SignedBigInteger { time }.multiplied_by(s_one_million_bigint);
auto offset = get_named_time_zone_offset_nanoseconds(system_time_zone_identifier, time_bigint);
auto offset = get_named_time_zone_offset_milliseconds(system_time_zone_identifier, time);
offset_nanoseconds = static_cast<double>(offset.offset.to_nanoseconds());
}

1
Userland/Libraries/LibJS/Runtime/Date.h
View file

@ -76,6 +76,7 @@ u16 ms_from_time(double);
Crypto::SignedBigInteger get_utc_epoch_nanoseconds(i32 year, u8 month, u8 day, u8 hour, u8 minute, u8 second, u16 millisecond, u16 microsecond, u16 nanosecond);
Vector<Crypto::SignedBigInteger> get_named_time_zone_epoch_nanoseconds(StringView time_zone_identifier, i32 year, u8 month, u8 day, u8 hour, u8 minute, u8 second, u16 millisecond, u16 microsecond, u16 nanosecond);
Unicode::TimeZoneOffset get_named_time_zone_offset_nanoseconds(StringView time_zone_identifier, Crypto::SignedBigInteger const& epoch_nanoseconds);
Unicode::TimeZoneOffset get_named_time_zone_offset_milliseconds(StringView time_zone_identifier, double epoch_milliseconds);
String system_time_zone_identifier();
void clear_system_time_zone_cache();
double local_time(double time);

3
Userland/Libraries/LibJS/Runtime/DatePrototype.cpp
View file

@ -1123,8 +1123,7 @@ ByteString time_zone_string(double time)
// 3. Else,
else {
// a. Let offsetNs be GetNamedTimeZoneOffsetNanoseconds(systemTimeZoneIdentifier, ℤ(ℝ(tv) × 10^6)).
auto time_bigint = Crypto::SignedBigInteger { time }.multiplied_by(Crypto::UnsignedBigInteger { 1'000'000 });
auto offset = get_named_time_zone_offset_nanoseconds(system_time_zone_identifier, time_bigint);
auto offset = get_named_time_zone_offset_milliseconds(system_time_zone_identifier, time);
offset_nanoseconds = static_cast<double>(offset.offset.to_nanoseconds());
in_dst = offset.in_dst;