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write_verilog: dump zero width sigspecs correctly. 

Before this commit, zero width sigspecs were dumped as "" (empty
string). Unfortunately, 1364-2005 5.2.3.3 indicates that an empty
string is equivalent to "\0", and is 8 bits wide, so that's wrong.

After this commit, a replication operation with a count of zero is
used instead, which is explicitly permitted per 1364-2005 5.1.14,
and is defined to have size zero. (Its operand has to have a non-zero
size for it to be legal, though.)

PR #1203 has addressed this issue before, but in an incomplete way.
This commit is contained in:
whitequark 2021-12-11 12:01:52 +00:00
parent 8e91857fab
commit 86f2804dc3
1 changed files with 2 additions and 1 deletions
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3
backends/verilog/verilog_backend.cc
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@ -358,7 +358,8 @@ void dump_sigchunk(std::ostream &f, const RTLIL::SigChunk &chunk, bool no_decima
void dump_sigspec(std::ostream &f, const RTLIL::SigSpec &sig)
{
if (GetSize(sig) == 0) {
f << "\"\"";
// See IEEE 1364-2005 Clause 5.1.14.
f << "{0{1'b0}}";
return;
}
if (sig.is_chunk()) {