From 261166d92b06a96b473b4434a68f7dc6cde77b7e Mon Sep 17 00:00:00 2001
From: Sebastien Bourdeauducq <sebastien@milkymist.org>
Date: Thu, 29 Nov 2012 22:59:54 +0100
Subject: [PATCH] fhdl/verilog: make signal behave as integers in arithmetic
 (MyHDL style)

See http://jandecaluwe.com/hdldesign/counting.html
---
 migen/fhdl/verilog.py | 56 +++++++++++++++++++++++++++----------------
 1 file changed, 36 insertions(+), 20 deletions(-)

diff --git a/migen/fhdl/verilog.py b/migen/fhdl/verilog.py
index b33476293..49c31e9eb 100644
--- a/migen/fhdl/verilog.py
+++ b/migen/fhdl/verilog.py
@@ -20,14 +20,14 @@ def _printsig(ns, s):
 def _printintbool(node):
 	if isinstance(node, bool):
 		if node:
-			return "1'd1"
+			return "1'd1", False
 		else:
-			return "1'd0"
+			return "1'd0", False
 	elif isinstance(node, int):
 		if node >= 0:
-			return str(bits_for(node)) + "'d" + str(node)
+			return str(bits_for(node)) + "'d" + str(node), False
 		else:
-			return "-" + str(bits_for(node)) + "'sd" + str(-node)
+			return "-" + str(bits_for(node)) + "'sd" + str(-node), True
 	else:
 		raise TypeError
 
@@ -35,16 +35,32 @@ def _printexpr(ns, node):
 	if isinstance(node, (int, bool)):
 		return _printintbool(node)
 	elif isinstance(node, Signal):
-		return ns.get_name(node)
+		return ns.get_name(node), node.signed
 	elif isinstance(node, _Operator):
 		arity = len(node.operands)
+		r1, s1 = _printexpr(ns, node.operands[0])
 		if arity == 1:
-			r = node.op + _printexpr(ns, node.operands[0])
+			if node.op == "-":
+				if s1:
+					r = node.op + r1
+				else:
+					r = "-$signed({1'd0, " + r1 + "})"
+				s = True
+			else:
+				r = node.op + r1
+				s = s1
 		elif arity == 2:
-			r = _printexpr(ns, node.operands[0]) + " " + node.op + " " + _printexpr(ns, node.operands[1])
+			r2, s2 = _printexpr(ns, node.operands[1])
+			if node.op in ["+", "-", "*", "&", "^", "|"]:
+				if s2 and not s1:
+					r1 = "$signed({1'd0, " + r1 + "})"
+				if s1 and not s2:
+					r2 = "$signed({1'd0, " + r2 + "})"
+			r = r1 + " " + node.op + " " + r2
+			s = s1 or s2
 		else:
 			raise TypeError
-		return "(" + r + ")"
+		return "(" + r + ")", s
 	elif isinstance(node, _Slice):
 		# Verilog does not like us slicing non-array signals...
 		if isinstance(node.value, Signal) \
@@ -56,13 +72,13 @@ def _printexpr(ns, node):
 			sr = "[" + str(node.start) + "]"
 		else:
 			sr = "[" + str(node.stop-1) + ":" + str(node.start) + "]"
-		return _printexpr(ns, node.value) + sr
+		r, s = _printexpr(ns, node.value)
+		return r + sr, s
 	elif isinstance(node, Cat):
-		l = list(map(partial(_printexpr, ns), node.l))
-		l.reverse()
-		return "{" + ", ".join(l) + "}"
+		l = [_printexpr(ns, v)[0] for v in reversed(node.l)]
+		return "{" + ", ".join(l) + "}", False
 	elif isinstance(node, Replicate):
-		return "{" + str(node.n) + "{" + _printexpr(ns, node.v) + "}}"
+		return "{" + str(node.n) + "{" + _printexpr(ns, node.v) + "}}", False
 	else:
 		raise TypeError
 
@@ -80,11 +96,11 @@ def _printnode(ns, at, level, node):
 			assignment = " = "
 		else:
 			assignment = " <= "
-		return "\t"*level + _printexpr(ns, node.l) + assignment + _printexpr(ns, node.r) + ";\n"
+		return "\t"*level + _printexpr(ns, node.l)[0] + assignment + _printexpr(ns, node.r)[0] + ";\n"
 	elif isinstance(node, list):
 		return "".join(list(map(partial(_printnode, ns, at, level), node)))
 	elif isinstance(node, If):
-		r = "\t"*level + "if (" + _printexpr(ns, node.cond) + ") begin\n"
+		r = "\t"*level + "if (" + _printexpr(ns, node.cond)[0] + ") begin\n"
 		r += _printnode(ns, at, level + 1, node.t)
 		if node.f:
 			r += "\t"*level + "end else begin\n"
@@ -93,10 +109,10 @@ def _printnode(ns, at, level, node):
 		return r
 	elif isinstance(node, Case):
 		if node.cases:
-			r = "\t"*level + "case (" + _printexpr(ns, node.test) + ")\n"
+			r = "\t"*level + "case (" + _printexpr(ns, node.test)[0] + ")\n"
 			css = sorted([(k, v) for (k, v) in node.cases.items() if k != "default"], key=itemgetter(0))
 			for choice, statements in css:
-				r += "\t"*(level + 1) + _printexpr(ns, choice) + ": begin\n"
+				r += "\t"*(level + 1) + _printexpr(ns, choice)[0] + ": begin\n"
 				r += _printnode(ns, at, level + 2, statements)
 				r += "\t"*(level + 1) + "end\n"
 			if "default" in node.cases:
@@ -176,7 +192,7 @@ def _printcomb(f, ns, display_run):
 				if display_run:
 					r += "\t$display(\"Running comb block #" + str(n) + "\");\n"
 				for t in g[0]:
-					r += "\t" + ns.get_name(t) + " <= " + _printexpr(ns, t.reset) + ";\n"
+					r += "\t" + ns.get_name(t) + " <= " + _printexpr(ns, t.reset)[0] + ";\n"
 				r += _printnode(ns, _AT_NONBLOCKING, 1, g[1])
 				r += syn_off
 				r += "\t" + ns.get_name(dummy_d) + " <= " + ns.get_name(dummy_s) + ";\n"
@@ -223,7 +239,7 @@ def _printinstances(f, ns, clock_domains):
 		for p in x.items:
 			if isinstance(p, Instance._IO):
 				name_inst = p.name
-				name_design = _printexpr(ns, p.expr)
+				name_design = _printexpr(ns, p.expr)[0]
 			elif isinstance(p, Instance.ClockPort):
 				name_inst = p.name_inst
 				name_design = ns.get_name(clock_domains[p.domain].clk)
@@ -259,7 +275,7 @@ def _printinit(f, ios, ns):
 	if signals:
 		r += "initial begin\n"
 		for s in sorted(signals, key=lambda x: x.huid):
-			r += "\t" + ns.get_name(s) + " <= " + _printexpr(ns, s.reset) + ";\n"
+			r += "\t" + ns.get_name(s) + " <= " + _printexpr(ns, s.reset)[0] + ";\n"
 		r += "end\n\n"
 	return r