SigSpec::extract to allow negative length

diff --git a/kernel/rtlil.cc b/kernel/rtlil.cc
index ebb6f5bf63be8b832bf336dbfc18c331d5f415c5..6f50821383ec19a060e348f2acddf14d36d15d1e 100644 (file)
--- a/kernel/rtlil.cc
+++ b/kernel/rtlil.cc
@@ -3353,7 +3353,7 @@ RTLIL::SigSpec RTLIL::SigSpec::extract(int offset, int length) const
 {
        unpack();
        cover("kernel.rtlil.sigspec.extract_pos");
-       return std::vector<RTLIL::SigBit>(bits_.begin() + offset, bits_.begin() + offset + length);
+       return std::vector<RTLIL::SigBit>(bits_.begin() + offset, length >= 0 ? bits_.begin() + offset + length : bits_.end() + length + 1);
 }
 
 void RTLIL::SigSpec::append(const RTLIL::SigSpec &signal)