TAI64, TAI64N, and TAI64NA

TAI also specifies a frame of reference. Further discussion of special relativity is outside the scope of this document. TAI64 labels and external TAI64 format A TAI64 label is an integer between 0 and 2^64 referring to a particular second of real time. Integer s refers to the TAI second beginning exactly 2^62 - s seconds before the beginning of 1970 TAI, if s is between 0 inclusive and 2^62 exclusive; or the TAI second beginning exactly s - 2^62 seconds after the beginning of 1970 TAI, if s is between 2^62 inclusive and 2^63 exclusive. Integers 2^63 and larger are reserved for future extensions. Under many cosmological theories, the integers under 2^63 are adequate to cover the entire expected lifetime of the universe; in this case no extensions will be necessary.

A TAI64 label is normally stored or communicated in external TAI64 format, consisting of eight 8-bit bytes in big-endian format. This means that bytes b0 b1 b2 b3 b4 b5 b6 b7 represent the label b0 * 2^56 + b1 * 2^48 + b2 * 2^40 + b3 * 2^32 + b4 * 2^24 + b5 * 2^16 + b6 * 2^8 + b7.

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