From 17163cf43a6b6eec9aac44f6a4463dda54b8ed68 Mon Sep 17 00:00:00 2001
From: Xiretza <xiretza@xiretza.xyz>
Date: Wed, 8 Apr 2020 19:30:47 +0200
Subject: Add flooring modulo operator

The $div and $mod cells use truncating division semantics (rounding
towards 0), as defined by e.g. Verilog. Another rounding mode, flooring
(rounding towards negative infinity), can be used in e.g. VHDL. The
new $modfloor cell provides this flooring modulo (also known as "remainder"
in several languages, but this name is ambiguous).

This commit also fixes the handling of $mod in opt_expr, which was
previously optimized as if it was $modfloor.
---
 backends/smv/smv.cc        | 5 +++--
 backends/smv/test_cells.sh | 4 ++--
 2 files changed, 5 insertions(+), 4 deletions(-)

(limited to 'backends/smv')

diff --git a/backends/smv/smv.cc b/backends/smv/smv.cc
index 7113ebc97..2fc7099f4 100644
--- a/backends/smv/smv.cc
+++ b/backends/smv/smv.cc
@@ -358,7 +358,8 @@ struct SmvWorker
 				continue;
 			}
 
-			if (cell->type.in(ID($div), ID($mod)))
+			// SMV has a "mod" operator, but its semantics don't seem to be well-defined - to be safe, don't generate it at all
+			if (cell->type.in(ID($div)/*, ID($mod), ID($modfloor)*/))
 			{
 				int width_y = GetSize(cell->getPort(ID::Y));
 				int width = max(width_y, GetSize(cell->getPort(ID::A)));
@@ -366,7 +367,7 @@ struct SmvWorker
 				string expr_a, expr_b, op;
 
 				if (cell->type == ID($div))  op = "/";
-				if (cell->type == ID($mod))  op = "mod";
+				//if (cell->type == ID($mod))  op = "mod";
 
 				if (cell->getParam(ID::A_SIGNED).as_bool())
 				{
diff --git a/backends/smv/test_cells.sh b/backends/smv/test_cells.sh
index 63de465c0..ae832ce00 100644
--- a/backends/smv/test_cells.sh
+++ b/backends/smv/test_cells.sh
@@ -7,8 +7,8 @@ mkdir -p test_cells.tmp
 cd test_cells.tmp
 
 # don't test $mul to reduce runtime
-# don't test $div and $mod to reduce runtime and avoid "div by zero" message
-../../../yosys -p 'test_cell -n 5 -w test all /$alu /$fa /$lcu /$lut /$macc /$mul /$div /$mod'
+# don't test $div/$mod/$modfloor to reduce runtime and avoid "div by zero" message
+../../../yosys -p 'test_cell -n 5 -w test all /$alu /$fa /$lcu /$lut /$macc /$mul /$div /$mod /$modfloor'
 
 cat > template.txt << "EOT"
 %module main
-- 
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