From e206b059f6f675e578b913b8d57155d345a51239 Mon Sep 17 00:00:00 2001
From: Robert O'Callahan <rocallahan@google.com>
Date: Fri, 29 Aug 2025 03:08:31 +0000
Subject: [PATCH] Make Const::Const(long long) constructor use packed bits
 internally if possible

---
 kernel/rtlil.cc                | 25 +++++++++++++++++++++++++
 kernel/rtlil.h                 |  3 ++-
 tests/unit/kernel/rtlilTest.cc | 25 +++++++++++++++++++++++++
 3 files changed, 52 insertions(+), 1 deletion(-)

diff --git a/kernel/rtlil.cc b/kernel/rtlil.cc
index cbb349a11..243098d54 100644
--- a/kernel/rtlil.cc
+++ b/kernel/rtlil.cc
@@ -221,9 +221,34 @@ RTLIL::Const::Const(const std::string &str)
 	tag = backing_tag::string;
 }
 
+RTLIL::Const::Const(long long val) // default width 32
+{
+	flags = RTLIL::CONST_FLAG_NONE;
+	char bytes[] = {
+		(char)(val >> 24), (char)(val >> 16), (char)(val >> 8), (char)val
+	};
+	new ((void*)&str_) std::string(bytes, 4);
+	tag = backing_tag::string;
+}
+
 RTLIL::Const::Const(long long val, int width)
 {
 	flags = RTLIL::CONST_FLAG_NONE;
+	if ((width & 7) == 0) {
+		new ((void*)&str_) std::string();
+		tag = backing_tag::string;
+		std::string& str = get_str();
+		int bytes = width >> 3;
+		signed char sign_byte = val < 0 ? -1 : 0;
+		str.resize(bytes, sign_byte);
+		bytes = std::min<int>(bytes, sizeof(val));
+		for (int i = 0; i < bytes; i++) {
+			str[str.size() - 1 - i] = val;
+			val = val >> 8;
+		}
+		return;
+	}
+
 	new ((void*)&bits_) bitvectype();
 	tag = backing_tag::bits;
 	bitvectype& bv = get_bits();
diff --git a/kernel/rtlil.h b/kernel/rtlil.h
index c1890452c..db407939e 100644
--- a/kernel/rtlil.h
+++ b/kernel/rtlil.h
@@ -744,7 +744,8 @@ private:
 public:
 	Const() : flags(RTLIL::CONST_FLAG_NONE), tag(backing_tag::bits), bits_(std::vector<RTLIL::State>()) {}
 	Const(const std::string &str);
-	Const(long long val, int width = 32);
+	Const(long long val); // default width is 32
+	Const(long long val, int width);
 	Const(RTLIL::State bit, int width = 1);
 	Const(std::vector<RTLIL::State> bits) : flags(RTLIL::CONST_FLAG_NONE), tag(backing_tag::bits), bits_(std::move(bits)) {}
 	Const(const std::vector<bool> &bits);
diff --git a/tests/unit/kernel/rtlilTest.cc b/tests/unit/kernel/rtlilTest.cc
index a9b7c3ada..0b7fbfd37 100644
--- a/tests/unit/kernel/rtlilTest.cc
+++ b/tests/unit/kernel/rtlilTest.cc
@@ -88,6 +88,31 @@ namespace RTLIL {
 			EXPECT_TRUE(cs1.is_bits());
 		}
 
+		{
+			Const c(0x12345678);
+			EXPECT_TRUE(c.is_str());
+			EXPECT_EQ(c.as_int(), 0x12345678);
+		}
+
+		{
+			Const c(0xab, 8);
+			EXPECT_TRUE(c.is_str());
+			EXPECT_EQ(c.as_int(), 0xab);
+		}
+
+		{
+			Const c(0x12345678, 80);
+			EXPECT_TRUE(c.is_str());
+			EXPECT_EQ(c.as_int(), 0x12345678);
+			EXPECT_EQ(c[79], S0);
+		}
+
+		{
+			Const c(-1, 80);
+			EXPECT_TRUE(c.is_str());
+			EXPECT_EQ(c.as_int(), -1);
+			EXPECT_EQ(c[79], S1);
+		}
 	}
 
 	TEST_F(KernelRtlilTest, ConstConstIteratorWorks) {