From b36e07962d0b29053c3701e256cd889c3c6e233c Mon Sep 17 00:00:00 2001
From: whitequark <cz@m-labs.hk>
Date: Sat, 28 Sep 2019 19:33:24 +0000
Subject: [PATCH] hdl.ast: actually implement the // operator.

---
 nmigen/back/pysim.py        |  4 ++++
 nmigen/back/rtlil.py        |  2 +-
 nmigen/hdl/ast.py           | 11 +++++++----
 nmigen/test/test_hdl_ast.py | 11 +++++++++++
 nmigen/test/test_sim.py     |  6 ++++++
 5 files changed, 29 insertions(+), 5 deletions(-)

diff --git a/nmigen/back/pysim.py b/nmigen/back/pysim.py
index 0f7e8c0..472cc57 100644
--- a/nmigen/back/pysim.py
+++ b/nmigen/back/pysim.py
@@ -146,6 +146,10 @@ class _RHSValueCompiler(_ValueCompiler):
                 return lambda state: normalize(lhs(state) -  rhs(state), shape)
             if value.op == "*":
                 return lambda state: normalize(lhs(state) *  rhs(state), shape)
+            if value.op == "//":
+                def floordiv(lhs, rhs):
+                    return 0 if rhs == 0 else lhs // rhs
+                return lambda state: normalize(floordiv(lhs(state), rhs(state)), shape)
             if value.op == "&":
                 return lambda state: normalize(lhs(state) &  rhs(state), shape)
             if value.op == "|":
diff --git a/nmigen/back/rtlil.py b/nmigen/back/rtlil.py
index 11823d4..e7ec34c 100644
--- a/nmigen/back/rtlil.py
+++ b/nmigen/back/rtlil.py
@@ -388,7 +388,7 @@ class _RHSValueCompiler(_ValueCompiler):
         (2, "+"):    "$add",
         (2, "-"):    "$sub",
         (2, "*"):    "$mul",
-        (2, "/"):    "$div",
+        (2, "//"):   "$div",
         (2, "%"):    "$mod",
         (2, "**"):   "$pow",
         (2, "<<"):   "$sshl",
diff --git a/nmigen/hdl/ast.py b/nmigen/hdl/ast.py
index 2dee3ff..6a68a67 100644
--- a/nmigen/hdl/ast.py
+++ b/nmigen/hdl/ast.py
@@ -87,10 +87,10 @@ class Value(metaclass=ABCMeta):
         return Operator("%", [self, other])
     def __rmod__(self, other):
         return Operator("%", [other, self])
-    def __div__(self, other):
-        return Operator("/", [self, other])
-    def __rdiv__(self, other):
-        return Operator("/", [other, self])
+    def __floordiv__(self, other):
+        return Operator("//", [self, other])
+    def __rfloordiv__(self, other):
+        return Operator("//", [other, self])
     def __lshift__(self, other):
         return Operator("<<", [self, other])
     def __rlshift__(self, other):
@@ -475,6 +475,9 @@ class Operator(Value):
                 return width + 1, signed
             if self.op == "*":
                 return a_width + b_width, a_signed or b_signed
+            if self.op == "//":
+                # division by -1 can overflow
+                return a_width + b_signed, a_signed or b_signed
             if self.op == "%":
                 return a_width, a_signed
             if self.op in ("<", "<=", "==", "!=", ">", ">="):
diff --git a/nmigen/test/test_hdl_ast.py b/nmigen/test/test_hdl_ast.py
index 143de35..0c4914b 100644
--- a/nmigen/test/test_hdl_ast.py
+++ b/nmigen/test/test_hdl_ast.py
@@ -181,6 +181,17 @@ class OperatorTestCase(FHDLTestCase):
         v5 = 10 * Const(0, 4)
         self.assertEqual(v5.shape(), (8, False))
 
+    def test_floordiv(self):
+        v1 = Const(0, (4, False)) // Const(0, (6, False))
+        self.assertEqual(repr(v1), "(// (const 4'd0) (const 6'd0))")
+        self.assertEqual(v1.shape(), (4, False))
+        v2 = Const(0, (4, True)) // Const(0, (6, True))
+        self.assertEqual(v2.shape(), (5, True))
+        v3 = Const(0, (4, True)) // Const(0, (4, False))
+        self.assertEqual(v3.shape(), (4, True))
+        v5 = 10 // Const(0, 4)
+        self.assertEqual(v5.shape(), (4, False))
+
     def test_and(self):
         v1 = Const(0, (4, False)) & Const(0, (6, False))
         self.assertEqual(repr(v1), "(& (const 4'd0) (const 6'd0))")
diff --git a/nmigen/test/test_sim.py b/nmigen/test/test_sim.py
index adfad0e..8126f1b 100644
--- a/nmigen/test/test_sim.py
+++ b/nmigen/test/test_sim.py
@@ -95,6 +95,12 @@ class SimulatorUnitTestCase(FHDLTestCase):
         self.assertStatement(stmt, [C(2,  4), C(2,  4)], C(4,   8))
         self.assertStatement(stmt, [C(7,  4), C(7,  4)], C(49,  8))
 
+    def test_floordiv(self):
+        stmt = lambda y, a, b: y.eq(a // b)
+        self.assertStatement(stmt, [C(2,  4), C(1,  4)], C(2,   8))
+        self.assertStatement(stmt, [C(2,  4), C(2,  4)], C(1,   8))
+        self.assertStatement(stmt, [C(7,  4), C(2,  4)], C(3,   8))
+
     def test_and(self):
         stmt = lambda y, a, b: y.eq(a & b)
         self.assertStatement(stmt, [C(0b1100, 4), C(0b1010, 4)], C(0b1000, 4))
-- 
2.30.2