This patch implements the swrite* and sformat system tasks. It also
makes $simtime distinguishable from the other integer time tasks.
This was needed to get the correct time units when $simtime was given
as an argument to $swrite*. The string constant code was also modified
to allow a string to be returned as a vector (0/1 bit pattern).
Here are some more specifics about the swrite* changes.
1. They do not share formatting code with the other display functions,
so they may/will produce different results.
2. All %{alpha} codes allow a width and justification. Others have been
enhanced (%t allows the default width and precision to be overridden,
time functions print with time formatting, better error checking and
messages, etc.).
3. %u and %z formatting codes have been added. It is important to note
that these two formats can produce embedded NULLs, since these
functions are returning a string anything after the first NULL will
not be reachable! memcpy is used instead of regular string processing
where needed so that the original string will contain the total
result. The size returned when the string is created is the true
length. A warning will be printed if a string with embedded NULLs is
produced (strlen() does not match the true length).
4. Real numbers are printed with %g instead of %f.
Once this new formatting code has been evaluated we should incorporate
the changes/fixes into the formatting code for the other functions or
the other functions could be modified to use this new code. The true
string length is available so we should be able to work around the
embedded NULL problem.
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