From: whitequark <whitequark@whitequark.org>
Date: Sun, 21 Apr 2019 07:16:59 +0000 (+0000)
Subject: hdl.ast: accept Signals with identical min/max bounds.
X-Git-Tag: working~9
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=33f9bd2a1d2c92c7c1c9d9d60151b93c554016b1;p=nmigen.git

hdl.ast: accept Signals with identical min/max bounds.

And produce a 0-bit signal.

Fixes #58.
---

diff --git a/nmigen/hdl/ast.py b/nmigen/hdl/ast.py
index 3a42220..37816ce 100644
--- a/nmigen/hdl/ast.py
+++ b/nmigen/hdl/ast.py
@@ -593,11 +593,15 @@ class Signal(Value, DUID):
             if max is None:
                 max = 2
             max -= 1  # make both bounds inclusive
-            if not min < max:
-                raise ValueError("Lower bound {} should be less than higher bound {}"
-                                 .format(min, max))
+            if min > max:
+                raise ValueError("Lower bound {} should be less or equal to higher bound {}"
+                                 .format(min, max + 1))
             self.signed = min < 0 or max < 0
-            self.nbits  = builtins.max(bits_for(min, self.signed), bits_for(max, self.signed))
+            if min == max:
+                self.nbits = 0
+            else:
+                self.nbits = builtins.max(bits_for(min, self.signed),
+                                          bits_for(max, self.signed))
 
         else:
             if not (min is None and max is None):
diff --git a/nmigen/test/test_hdl_ast.py b/nmigen/test/test_hdl_ast.py
index 608870f..d2cc4cd 100644
--- a/nmigen/test/test_hdl_ast.py
+++ b/nmigen/test/test_hdl_ast.py
@@ -414,13 +414,18 @@ class SignalTestCase(FHDLTestCase):
         self.assertEqual(s8.shape(), (6, True))
         s9 = Signal(0)
         self.assertEqual(s9.shape(), (0, False))
+        s10 = Signal(max=1)
+        self.assertEqual(s10.shape(), (0, False))
 
     def test_shape_bad(self):
-        with self.assertRaises(ValueError):
+        with self.assertRaises(ValueError,
+                msg="Lower bound 10 should be less or equal to higher bound 4"):
             Signal(min=10, max=4)
-        with self.assertRaises(ValueError):
+        with self.assertRaises(ValueError,
+                msg="Only one of bits/signedness or bounds may be specified"):
             Signal(2, min=10)
-        with self.assertRaises(TypeError):
+        with self.assertRaises(TypeError,
+                msg="Width must be a non-negative integer, not '-10'"):
             Signal(-10)
 
     def test_name(self):