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hdl.ast: warn on fencepost error in Signal(range(x), reset=x).

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Also, relax the language reference inset from "warning" to "note"
since this is no longer something developers have to keep in mind
explicitly.
This commit is contained in:
Catherine 2023-03-13 20:27:13 +00:00
parent 32eabd9372
commit 80343d1c4c
3 changed files with 33 additions and 4 deletions
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docs/lang.rst
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@ -163,7 +163,7 @@ Specifying a shape with a range is convenient for counters, indexes, and all oth
.. _lang-exclrange:
.. warning::
.. note::
Python ranges are *exclusive* or *half-open*, meaning they do not contain their ``.stop`` element. Because of this, values with shapes cast from a ``range(stop)`` where ``stop`` is a power of 2 are not wide enough to represent ``stop`` itself:
@ -175,7 +175,7 @@ Specifying a shape with a range is convenient for counters, indexes, and all oth
>>> fencepost.value
0
Be mindful of this edge case!
Amaranth detects uses of :class:`Const` and :class:`Signal` that invoke such an off-by-one error, and emits a diagnostic message.
.. _lang-shapeenum: