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"use strict";
// This files implements the calculation of the offset between the global monotonic clock and UNIX time. This value is
// known as |t1| in the calculation of "time origin timestamp" in the spec. This value needs to be calculated once and
// can be used in all subsequent Performance instances.
//
// However, if the clock is not fast enough, the export is undefined to signify that we should use Date.now() to get the
// time origin timestamp with millisecond accuracy, per spec.
const { getGlobalMonotonicClockMS } = require("./global-monotonic-clock");
const clockIsAccurate = require("./clock-is-accurate");
// This function assumes the clock is accurate.
function calculateClockOffset() {
const start = Date.now();
let cur = start;
// Limit the iterations, just in case we're running in an environment where Date.now() has been mocked and is
// constant.
for (let i = 0; i < 1e6 && cur === start; i++) {
cur = Date.now();
}
// At this point |cur| "just" became equal to the next millisecond -- the unseen digits after |cur| are approximately
// all 0, and |cur| is the closest to the actual value of the UNIX time. Now, get the current global monotonic clock
// value and do the remaining calculations.
return cur - getGlobalMonotonicClockMS();
}
if (clockIsAccurate) {
// Warm up the function.
calculateClockOffset();
calculateClockOffset();
calculateClockOffset();
module.exports = calculateClockOffset;
} else {
module.exports = undefined;
}
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