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Re: Exposing subsecond precision in current-seconds

From: Lassi Kortela
Subject: Re: Exposing subsecond precision in current-seconds
Date: Mon, 27 Apr 2020 21:57:18 +0300
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Sorry, I meant to write microseconds.

No problem. In that case, please take a look at Gambit's time API: <>. It uses a float for the internal representation of time objects. `time->seconds` extracts it an ordinary float out of it. Perhaps the same interface could be used in Chicken.

For nanoseconds precision you'd need to
use `clock_gettime` which is harder to emulate on Windows than `gettimeofday`.

The main point of nanosecond precision in Scheme is to preserve bit-for-bit precise timestamps from Unix file system APIs (in case you copy the timestamp elsewhere and somebody later compares it for exact equality with the original). NTFS timestamps have 100-nsec precision, so a (seconds nanoseconds) pair is good for them as well.

It's unlikely that useful ns-level accuracy for the current time is obtainable in any Scheme program (or any program generally). System call overhead is measured in microseconds. I guess CPU cycle counters in theory have nanosecond accuracy, but those are useful mainly in computing the time elapsed between two counters, not in reference to exact moments on a standard timescale like UTC.

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