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TimeCowan

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== Time ==

`(current-posix-millisecond)`

Returns a rational number representing the current millisecond of the Posix epoch, which began on 00:00:00 on 1 January 1970, Coordinated Universal Time but excludes all leap seconds.  Implementations SHOULD return a value that is:

 * As accurate as reasonably achievable.
 * Provides at least 1-second precision.
 * Provides a range of at least 2^31^ seconds before and after the epoch.
.
Implementations MAY return exact or inexact values, and SHOULD return inexact values unless:

 * The value is an integer.
 * The range of most-efficiently-implemented exact integers in the implementation exceeds the integer range of inexact rationals.

In practice this means that implementations with fixnums greater than 2^53^ should return fixnums unless they have time-of-day clocks that provide more than 1 ms precision, and all other implementations should return IEEE 64-bit floats.

If the implementation cannot provide the time when `current-posix-milliseconds` is called (either temporarily or permanently), it MUST return `#f`.

Note that there is about a 1 in 10^-8^ probability that a computation of elapsed
time made by calling this procedure twice will be off by 1 second, given the number of leap seconds between 1972 and 2011.

== Date and Time Arithmetic (WG2) ==

See TimeAdvancedCowan.

== Time Durations and Periods (WG2) ==

See TimePeriodsCowan.

== Time formatting (WG2) ==

See TimeFormattingCowan.

time

2010-11-27 09:46:16