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3.2 Stamp resolution

Regarding RCS, recorded timestamps come into play in two places:

• The delta production of the file format grammar includes component date (see File format grammar). The recorded information has second (whole number) resolution.
• The metadata of a file on the filesystem usually includes its modification time. The resolution of this information depends on the capabilities of the filesystem; modern ones — e.g., ext4 — tend to support subsecond (fractional) resolution.

Historically, up through version 5.9.4, RCS behaved “agnostically” with respect to the subsecond component of the file modification time, relying on the operating system and filesystem to take care of things at whatever resolution was available at the time, with the single exception of the ‘-T’ option (see Misc common options). In the presence of this option, RCS would:

• (reading) Ignore the subsecond component.
• (writing) Specify 0 as the subsecond component.

For versions after 5.9.4, if the filesystem supports it, RCS reads and writes file modification time with subsecond resolution, given the ‘-T’ option.

It’s important to keep in mind that by design, the delta date component is limited to second resolution, so subsecond resolution is only guaranteed for operations where the file modification time originates from a file actually existing on the filesystem (i.e., via the stat(2) system call).