`tval.tv_usec` is a (signed) `long` and `ssPrec->m_offset` is an
`unsigned int`. Clang warns upon realizing that we are attempting to
divide a signed `long` with an `unsigned int`.
Casting the `long` to `unsigned long` makes both operands `unsigned` and
allows for auto conversion to `size_t`.
The `size_t` cast is to make it apparent that the cast is correct.
Vasily
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