From 4cd2e04da41fd4e53c17c0b695f1d61060e19856 Mon Sep 17 00:00:00 2001
From: Philippe Sauter <phsauter@iis.ee.ethz.ch>
Date: Thu, 19 Sep 2024 18:06:42 +0200
Subject: [PATCH] rtlil: add Const::compress helper function

Compresses the current bits to the minimum
width representation by removing leading bits.
---
 kernel/rtlil.cc | 24 ++++++++++++++++++++++++
 kernel/rtlil.h  |  3 +++
 2 files changed, 27 insertions(+)

diff --git a/kernel/rtlil.cc b/kernel/rtlil.cc
index 2d3135378..0a3d2082d 100644
--- a/kernel/rtlil.cc
+++ b/kernel/rtlil.cc
@@ -280,6 +280,30 @@ int RTLIL::Const::as_int(bool is_signed) const
 	return ret;
 }
 
+void RTLIL::Const::compress(bool is_signed)
+{
+	if (bits.empty()) return;
+
+	// back to front (MSB to LSB)
+	RTLIL::State leading_bit;
+	if(is_signed)
+		leading_bit = (bits.back() == RTLIL::State::Sx) ? RTLIL::State::S0 : bits.back();
+	else
+		leading_bit = RTLIL::State::S0;
+
+    size_t idx = bits.size();
+    while (idx > 0 && bits[idx -1] == leading_bit) {
+        --idx;
+    }
+
+	// signed needs one leading bit
+	if (is_signed && idx < bits.size()) {
+        ++idx;
+    }
+
+	bits.erase(bits.begin() + idx, bits.end());
+}
+
 std::string RTLIL::Const::as_string() const
 {
 	std::string ret;
diff --git a/kernel/rtlil.h b/kernel/rtlil.h
index c49734cd0..7f47bf288 100644
--- a/kernel/rtlil.h
+++ b/kernel/rtlil.h
@@ -703,6 +703,9 @@ struct RTLIL::Const
 		return ret;
 	}
 
+	// compress representation to the minimum required bits
+	void compress(bool is_signed = false);
+
 	void extu(int width) {
 		bits.resize(width, RTLIL::State::S0);
 	}