rtlil: add Const:: as_int_compressed function

kernel/rtlil.cc

@@ -28,6 +28,7 @@
 
 #include <string.h>
 #include <algorithm>
+#include <optional>
 
 YOSYS_NAMESPACE_BEGIN
 
@@ -280,9 +281,9 @@ int RTLIL::Const::as_int(bool is_signed) const
 	return ret;
 }
 
-void RTLIL::Const::compress(bool is_signed)
+size_t RTLIL::Const::get_min_size(bool is_signed) const
 {
-	if (bits.empty()) return;
+	if (bits.empty()) return 0;
 
 	// back to front (MSB to LSB)
 	RTLIL::State leading_bit;
@@ -301,11 +302,31 @@ void RTLIL::Const::compress(bool is_signed)
 		idx++;
 	}
 	// must be at least one bit
-	idx = (idx == 0) ? 1 : idx;
+	return (idx == 0) ? 1 : idx;
+}
 
+void RTLIL::Const::compress(bool is_signed)
+{
+	size_t idx = get_min_size(is_signed);
 	bits.erase(bits.begin() + idx, bits.end());
 }
 
+std::optional<int> RTLIL::Const::as_int_compress(bool is_signed) const
+{
+	size_t size = get_min_size(is_signed);
+	if(size == 0 || size > 32)
+		return std::nullopt;
+
+	int32_t ret = 0;
+	for (size_t i = 0; i < size && i < 32; i++)
+		if (bits[i] == State::S1)
+			ret |= 1 << i;
+	if (is_signed && bits[size-1] == State::S1)
+		for (size_t i = size; i < 32; i++)
+			ret |= 1 << i;
+	return ret;
+}
+
 std::string RTLIL::Const::as_string() const
 {
 	std::string ret;

kernel/rtlil.h

@@ -703,9 +703,14 @@ struct RTLIL::Const
 		return ret;
 	}
 
+	// find the MSB without redundant leading bits
+	size_t get_min_size(bool is_signed) const;
+
 	// compress representation to the minimum required bits
 	void compress(bool is_signed = false);
 
+	std::optional<int> as_int_compress(bool is_signed) const;
+
 	void extu(int width) {
 		bits.resize(width, RTLIL::State::S0);
 	}