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

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And produce a 0-bit signal.

Fixes #58.
This commit is contained in:
whitequark 2019-04-21 07:16:59 +00:00
parent 083016d747
commit 33f9bd2a1d
2 changed files with 16 additions and 7 deletions
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12
nmigen/hdl/ast.py
View file

@ -593,11 +593,15 @@ class Signal(Value, DUID):
if max is None: if max is None:
max = 2 max = 2
max -= 1 # make both bounds inclusive max -= 1 # make both bounds inclusive
if not min < max: if min > max:
raise ValueError("Lower bound {} should be less than higher bound {}" raise ValueError("Lower bound {} should be less or equal to higher bound {}"
.format(min, max)) .format(min, max + 1))
self.signed = min < 0 or max < 0 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: else:
if not (min is None and max is None): if not (min is None and max is None):

11
nmigen/test/test_hdl_ast.py
View file

@ -414,13 +414,18 @@ class SignalTestCase(FHDLTestCase):
self.assertEqual(s8.shape(), (6, True)) self.assertEqual(s8.shape(), (6, True))
s9 = Signal(0) s9 = Signal(0)
self.assertEqual(s9.shape(), (0, False)) self.assertEqual(s9.shape(), (0, False))
s10 = Signal(max=1)
self.assertEqual(s10.shape(), (0, False))
def test_shape_bad(self): 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) 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) Signal(2, min=10)
with self.assertRaises(TypeError): with self.assertRaises(TypeError,
msg="Width must be a non-negative integer, not '-10'"):
Signal(-10) Signal(-10)
def test_name(self): def test_name(self):