hdl.ast: add Signal.range(...), to replace Signal(min=..., max=...).

Fixes #196.

nmigen/hdl/ast.py

@@ -1,6 +1,7 @@
 from abc import ABCMeta, abstractmethod
 import builtins
 import traceback
+import warnings
 from collections import OrderedDict
 from collections.abc import Iterable, MutableMapping, MutableSet, MutableSequence
 from enum import Enum
@@ -627,6 +628,13 @@ class Signal(Value, DUID):
                  attrs=None, decoder=None, src_loc_at=0):
         super().__init__(src_loc_at=src_loc_at)
 
+        # TODO(nmigen-0.2): move this to nmigen.compat and make it a deprecated extension
+        if min is not None or max is not None:
+            warnings.warn("instead of `Signal(min={min}, max={max})`, "
+                          "use `Signal.range({min}, {max})`"
+                          .format(min=min or 0, max=max or 2),
+                          DeprecationWarning, stacklevel=2 + src_loc_at)
+
         if name is not None and not isinstance(name, str):
             raise TypeError("Name must be a string, not '{!r}'".format(name))
         self.name = name or tracer.get_var_name(depth=2 + src_loc_at, default="$signal")
@@ -671,6 +679,23 @@ class Signal(Value, DUID):
         else:
             self.decoder = decoder
 
+    @classmethod
+    def range(cls, *args, src_loc_at=0, **kwargs):
+        """Create Signal that can represent a given range.
+
+        The parameters to ``Signal.range`` are the same as for the built-in ``range`` function.
+        That is, for any given ``range(*args)``, ``Signal.range(*args)`` can represent any
+        ``x for x in range(*args)``.
+        """
+        value_range = range(*args)
+        if len(value_range) > 0:
+            signed = value_range.start < 0 or (value_range.stop - value_range.step) < 0
+        else:
+            signed = value_range.start < 0
+        nbits  = max(bits_for(value_range.start, signed),
+                     bits_for(value_range.stop - value_range.step, signed))
+        return cls((nbits, signed), src_loc_at=1 + src_loc_at, **kwargs)
+
     @classmethod
     def like(cls, other, *, name=None, name_suffix=None, src_loc_at=0, **kwargs):
         """Create Signal based on another.

nmigen/test/test_hdl_ast.py

@@ -1,3 +1,4 @@
+import warnings
 from enum import Enum
 
 from ..hdl.ast import *
@@ -297,7 +298,7 @@ class SliceTestCase(FHDLTestCase):
 class BitSelectTestCase(FHDLTestCase):
     def setUp(self):
         self.c = Const(0, 8)
-        self.s = Signal(max=self.c.nbits)
+        self.s = Signal.range(self.c.nbits)
 
     def test_shape(self):
         s1 = self.c.bit_select(self.s, 2)
@@ -321,7 +322,7 @@ class BitSelectTestCase(FHDLTestCase):
 class WordSelectTestCase(FHDLTestCase):
     def setUp(self):
         self.c = Const(0, 8)
-        self.s = Signal(max=self.c.nbits)
+        self.s = Signal.range(self.c.nbits)
 
     def test_shape(self):
         s1 = self.c.word_select(self.s, 2)
@@ -390,8 +391,8 @@ class ArrayTestCase(FHDLTestCase):
 
     def test_becomes_immutable(self):
         a = Array([1,2,3])
-        s1 = Signal(max=len(a))
+        s1 = Signal.range(len(a))
-        s2 = Signal(max=len(a))
+        s2 = Signal.range(len(a))
         v1 = a[s1]
         v2 = a[s2]
         with self.assertRaisesRegex(ValueError,
@@ -407,7 +408,7 @@ class ArrayTestCase(FHDLTestCase):
     def test_repr(self):
         a = Array([1,2,3])
         self.assertEqual(repr(a), "(array mutable [1, 2, 3])")
-        s = Signal(max=len(a))
+        s = Signal.range(len(a))
         v = a[s]
         self.assertEqual(repr(a), "(array [1, 2, 3])")
 
@@ -415,8 +416,8 @@ class ArrayTestCase(FHDLTestCase):
 class ArrayProxyTestCase(FHDLTestCase):
     def test_index_shape(self):
         m = Array(Array(x * y for y in range(1, 4)) for x in range(1, 4))
-        a = Signal(max=3)
+        a = Signal.range(3)
-        b = Signal(max=3)
+        b = Signal.range(3)
         v = m[a][b]
         self.assertEqual(v.shape(), (4, False))
 
@@ -424,14 +425,14 @@ class ArrayProxyTestCase(FHDLTestCase):
         from collections import namedtuple
         pair = namedtuple("pair", ("p", "n"))
         a = Array(pair(i, -i) for i in range(10))
-        s = Signal(max=len(a))
+        s = Signal.range(len(a))
         v = a[s]
         self.assertEqual(v.p.shape(), (4, False))
         self.assertEqual(v.n.shape(), (6, True))
 
     def test_repr(self):
         a = Array([1, 2, 3])
-        s = Signal(max=3)
+        s = Signal.range(3)
         v = a[s]
         self.assertEqual(repr(v), "(proxy (array [1, 2, 3]) (sig s))")
 
@@ -446,30 +447,52 @@ class SignalTestCase(FHDLTestCase):
         self.assertEqual(s3.shape(), (2, False))
         s4 = Signal((2, True))
         self.assertEqual(s4.shape(), (2, True))
-        s5 = Signal(max=16)
+        s5 = Signal(0)
-        self.assertEqual(s5.shape(), (4, False))
+        self.assertEqual(s5.shape(), (0, False))
-        s6 = Signal(min=4, max=16)
+        s6 = Signal.range(16)
         self.assertEqual(s6.shape(), (4, False))
-        s7 = Signal(min=-4, max=16)
+        s7 = Signal.range(4, 16)
-        self.assertEqual(s7.shape(), (5, True))
+        self.assertEqual(s7.shape(), (4, False))
-        s8 = Signal(min=-20, max=16)
+        s8 = Signal.range(-4, 16)
-        self.assertEqual(s8.shape(), (6, True))
+        self.assertEqual(s8.shape(), (5, True))
-        s9 = Signal(0)
+        s9 = Signal.range(-20, 16)
-        self.assertEqual(s9.shape(), (0, False))
+        self.assertEqual(s9.shape(), (6, True))
-        s10 = Signal(max=1)
+        s10 = Signal.range(0)
-        self.assertEqual(s10.shape(), (0, False))
+        self.assertEqual(s10.shape(), (1, False))
+        s11 = Signal.range(1)
+        self.assertEqual(s11.shape(), (1, False))
+        # deprecated
+        with warnings.catch_warnings():
+            warnings.filterwarnings(action="ignore", category=DeprecationWarning)
+            d6 = Signal(max=16)
+            self.assertEqual(d6.shape(), (4, False))
+            d7 = Signal(min=4, max=16)
+            self.assertEqual(d7.shape(), (4, False))
+            d8 = Signal(min=-4, max=16)
+            self.assertEqual(d8.shape(), (5, True))
+            d9 = Signal(min=-20, max=16)
+            self.assertEqual(d9.shape(), (6, True))
+            d10 = Signal(max=1)
+            self.assertEqual(d10.shape(), (0, False))
 
     def test_shape_bad(self):
-        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,
-                msg="Only one of bits/signedness or bounds may be specified"):
-            Signal(2, min=10)
         with self.assertRaises(TypeError,
                 msg="Width must be a non-negative integer, not '-10'"):
             Signal(-10)
 
+    def test_min_max_deprecated(self):
+        with self.assertWarns(DeprecationWarning,
+                msg="instead of `Signal(min=0, max=10)`, use `Signal.range(0, 10)`"):
+            Signal(max=10)
+        with warnings.catch_warnings():
+            warnings.filterwarnings(action="ignore", category=DeprecationWarning)
+            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,
+                    msg="Only one of bits/signedness or bounds may be specified"):
+                Signal(2, min=10)
+
     def test_name(self):
         s1 = Signal()
         self.assertEqual(s1.name, "s1")
@@ -500,7 +523,7 @@ class SignalTestCase(FHDLTestCase):
     def test_like(self):
         s1 = Signal.like(Signal(4))
         self.assertEqual(s1.shape(), (4, False))
-        s2 = Signal.like(Signal(min=-15))
+        s2 = Signal.like(Signal.range(-15, 1))
         self.assertEqual(s2.shape(), (5, True))
         s3 = Signal.like(Signal(4, reset=0b111, reset_less=True))
         self.assertEqual(s3.reset, 0b111)