Use undef (x/z vs. NaN) rules for real values from IEEE Std 1800-2012

2 files changed, 11 insertions, 0 deletions

diff --git a/frontends/ast/ast.cc b/frontends/ast/ast.cc
index 967111d3..3f704bea 100644
--- a/frontends/ast/ast.cc
+++ b/frontends/ast/ast.cc
@@ -783,6 +783,8 @@ double AstNode::asReal(bool is_signed)
 
 		double v = 0;
 		for (size_t i = 0; i < val.bits.size(); i++)
+			// IEEE Std 1800-2012 Par 6.12.2: Individual bits that are x or z in
+			// the net or the variable shall be treated as zero upon conversion.
 			if (val.bits.at(i) == RTLIL::State::S1)
 				v += exp2(i);
 		if (is_negative)
diff --git a/frontends/ast/simplify.cc b/frontends/ast/simplify.cc
index 80fd28d5..3f712510 100644
--- a/frontends/ast/simplify.cc
+++ b/frontends/ast/simplify.cc
@@ -1625,6 +1625,15 @@ skip_dynamic_range_lvalue_expansion:;
 						if (a.bits[i] != b.bits[i])
 							a.bits[i] = RTLIL::State::Sx;
 					newNode = mkconst_bits(a.bits, sign_hint);
+				} else if (children[1]->isConst() && children[2]->isConst()) {
+					newNode = new AstNode(AST_REALVALUE);
+					if (children[1]->asReal(sign_hint) == children[2]->asReal(sign_hint))
+						newNode->realvalue = children[1]->asReal(sign_hint);
+					else
+						// IEEE Std 1800-2012 Sec. 11.4.11 states that the entry in Table 7-1 for
+						// the data type in question should be returned if the ?: is ambiguous. The
+						// value in Table 7-1 for the 'real' type is 0.0.
+						newNode->realvalue = 0.0;
 				}
 			}
 			break;