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write_verilog: dump zero width constants correctly. 

Before this commit, zero width constants 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.)

Fixes #948 (again).
This commit is contained in:
whitequark 2019-07-16 20:57:05 +00:00
parent f8e470c1d1
commit 4ff44d85a5
1 changed files with 2 additions and 1 deletions
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3
backends/verilog/verilog_backend.cc
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@ -189,7 +189,8 @@ void dump_const(std::ostream &f, const RTLIL::Const &data, int width = -1, int o
if (width < 0)
width = data.bits.size() - offset;
if (width == 0) {
f << "\"\"";
// See IEEE 1364-2005 Clause 5.1.14.
f << "{0{1'b0}}";
return;
}
if (nostr)