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std.time: Make Instant.since() work on UEFI

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Linus Groh 2025-03-02 22:31:47 +00:00
parent 1a03b8c899
commit 3bea47883a
1 changed files with 31 additions and 29 deletions
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60
lib/std/time.zig
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@ -135,7 +135,7 @@ pub const Instant = struct {
const clock_id = switch (builtin.os.tag) {
.windows => {
// QPC on windows doesn't fail on >= XP/2000 and includes time suspended.
return Instant{ .timestamp = windows.QueryPerformanceCounter() };
return .{ .timestamp = windows.QueryPerformanceCounter() };
},
.wasi => {
var ns: std.os.wasi.timestamp_t = undefined;
@ -147,7 +147,7 @@ pub const Instant = struct {
var value: std.os.uefi.Time = undefined;
const status = std.os.uefi.system_table.runtime_services.getTime(&value, null);
if (status != .success) return error.Unsupported;
return Instant{ .timestamp = value.toEpoch() };
return .{ .timestamp = value.toEpoch() };
},
// On darwin, use UPTIME_RAW instead of MONOTONIC as it ticks while
// suspended.
@ -185,36 +185,38 @@ pub const Instant = struct {
/// This assumes that the `earlier` Instant represents a moment in time before or equal to `self`.
/// This also assumes that the time that has passed between both Instants fits inside a u64 (~585 yrs).
pub fn since(self: Instant, earlier: Instant) u64 {
if (builtin.os.tag == .windows) {
// We don't need to cache QPF as it's internally just a memory read to KUSER_SHARED_DATA
// (a read-only page of info updated and mapped by the kernel to all processes):
// https://docs.microsoft.com/en-us/windows-hardware/drivers/ddi/ntddk/ns-ntddk-kuser_shared_data
// https://www.geoffchappell.com/studies/windows/km/ntoskrnl/inc/api/ntexapi_x/kuser_shared_data/index.htm
const qpc = self.timestamp - earlier.timestamp;
const qpf = windows.QueryPerformanceFrequency();
switch (builtin.os.tag) {
.windows => {
// We don't need to cache QPF as it's internally just a memory read to KUSER_SHARED_DATA
// (a read-only page of info updated and mapped by the kernel to all processes):
// https://docs.microsoft.com/en-us/windows-hardware/drivers/ddi/ntddk/ns-ntddk-kuser_shared_data
// https://www.geoffchappell.com/studies/windows/km/ntoskrnl/inc/api/ntexapi_x/kuser_shared_data/index.htm
const qpc = self.timestamp - earlier.timestamp;
const qpf = windows.QueryPerformanceFrequency();
// 10Mhz (1 qpc tick every 100ns) is a common enough QPF value that we can optimize on it.
// https://github.com/microsoft/STL/blob/785143a0c73f030238ef618890fd4d6ae2b3a3a0/stl/inc/chrono#L694-L701
const common_qpf = 10_000_000;
if (qpf == common_qpf) {
return qpc * (ns_per_s / common_qpf);
}
// 10Mhz (1 qpc tick every 100ns) is a common enough QPF value that we can optimize on it.
// https://github.com/microsoft/STL/blob/785143a0c73f030238ef618890fd4d6ae2b3a3a0/stl/inc/chrono#L694-L701
const common_qpf = 10_000_000;
if (qpf == common_qpf) {
return qpc * (ns_per_s / common_qpf);
}
// Convert to ns using fixed point.
const scale = @as(u64, std.time.ns_per_s << 32) / @as(u32, @intCast(qpf));
const result = (@as(u96, qpc) * scale) >> 32;
return @as(u64, @truncate(result));
// Convert to ns using fixed point.
const scale = @as(u64, std.time.ns_per_s << 32) / @as(u32, @intCast(qpf));
const result = (@as(u96, qpc) * scale) >> 32;
return @as(u64, @truncate(result));
},
.uefi, .wasi => {
// UEFI and WASI timestamps are directly in nanoseconds
return self.timestamp - earlier.timestamp;
},
else => {
// Convert timespec diff to ns
const seconds = @as(u64, @intCast(self.timestamp.sec - earlier.timestamp.sec));
const elapsed = (seconds * ns_per_s) + @as(u32, @intCast(self.timestamp.nsec));
return elapsed - @as(u32, @intCast(earlier.timestamp.nsec));
},
}
// WASI timestamps are directly in nanoseconds
if (builtin.os.tag == .wasi) {
return self.timestamp - earlier.timestamp;
}
// Convert timespec diff to ns
const seconds = @as(u64, @intCast(self.timestamp.sec - earlier.timestamp.sec));
const elapsed = (seconds * ns_per_s) + @as(u32, @intCast(self.timestamp.nsec));
return elapsed - @as(u32, @intCast(earlier.timestamp.nsec));
}
};