Re: Enhancement: Dynamic Values on attributes.

From: Steven Sharp (sharp@cadence.com)
Date: Tue Nov 04 2003 - 13:11:04 PST

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    >$itos and $stoi would be very useful.
    >We have often had need for such.

    I assume that most of the need for $itos and $stoi can be met by the
    Verilog-2001 system tasks $swrite and $sscanf with %d formats, though
    they may not be as convenient as function versions in some situations.

    I don't know if you were reading the details of the earlier discussion,
    but there are some issues with function versions. All operands in
    Verilog expressions must have known widths at compile time, including
    system functions. This width can depend on things known at compile
    time (such as the width of the arguments), but not on things that are
    not known at compile time (such as the values of variables). So if you
    want $itos to accept variable arguments and be able to produce the
    correct string for the maximum possible value of the arguments, the
    result must be as wide as that maximum possible value needs. And that
    means that it will be that wide even for smaller values.

    For example, a 32-bit signed integer requires 10 decimal digits to
    represent the maximum value, 11 if you allow for a negative sign. That
    means an 80 or 88 bit wide vector result. Even if the argument turns out
    to be 1, the result would still be 88 bits wide. The lowest byte would
    presumably be the ASCII character "1", but what should be used for the
    upper bytes? The obvious candidates are:

    - zero-extend the value with zero bits (creating NUL bytes). This is
      what you would get if you assigned the shorter string "1" to the larger
      80 or 88 bit wide vector.

    - zero-pad the numeric field with "0" characters (e.g. "00000000001"
      or maybe " 00000000001" or "+00000000001" if we had to leave space for
      a negative sign). The first is how binary or hex values get printed
      by $display. There is no example of the signed situations since binary
      and hex formats print as unsigned and decimal format can print a sign
      but doesn't print leading zeros. Some version of this might work for
      Krishna's back-end tools, since they may be able to parse numbers with
      leading zeros.
      
    - pad with spaces (e.g. " 1"). This is how decimal values are
      printed by $display.

    Steven Sharp
    sharp@cadence.com

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