From f24f1b02e871d8c7af9ead26c615645ccfcb0016 Mon Sep 17 00:00:00 2001 From: whitequark Date: Thu, 2 Jul 2020 23:11:35 +0000 Subject: [PATCH] docs/lang: document constshifts. --- docs/lang.rst | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) diff --git a/docs/lang.rst b/docs/lang.rst index 47475b7..dc6a287 100644 --- a/docs/lang.rst +++ b/docs/lang.rst @@ -484,26 +484,27 @@ Operation Description Notes ``a << b`` left shift by variable amount [#opB2]_ ``a.rotate_left(i)`` left rotate by constant amount [#opB3]_ ``a.rotate_right(i)`` right rotate by constant amount [#opB3]_ +``a.shift_left(i)`` left shift by constant amount [#opB3]_ +``a.shift_right(i)`` right shift by constant amount [#opB3]_ ===================== ========================================== ====== .. _IMPLY: https://en.wikipedia.org/wiki/IMPLY_gate .. [#opB1] Logical and arithmetic right shift of an unsigned value are equivalent. Logical right shift of a signed value can be expressed by :ref:`converting it to unsigned ` first. .. [#opB2] Shift amount must be unsigned; integer shifts in Python require the amount to be positive. -.. [#opB3] Rotate amount can be negative, in which case the direction is reversed. -.. TODO: add constshifts https://github.com/nmigen/nmigen/issues/378 +.. [#opB3] Shift and rotate amounts can be negative, in which case the direction is reversed. .. _lang-hugeshift: .. note:: - Because nMigen ensures that the width of a left shift expression is wide enough to represent any possible result, left shift by a wide amount produces exponentially wider intermediate values, stressing the synthesis tools: + Because nMigen ensures that the width of a variable left shift expression is wide enough to represent any possible result, variable left shift by a wide amount produces exponentially wider intermediate values, stressing the synthesis tools: .. doctest:: >>> (1 << C(0, 32)).shape() unsigned(4294967296) - Although nMigen will detect and reject expressions wide enough to break other tools, it is a good practice to explicitly limit the width of a non-constant shift amount in a left shift. + Although nMigen will detect and reject expressions wide enough to break other tools, it is a good practice to explicitly limit the width of a shift amount in a variable left shift. .. _lang-reduceops: -- 2.30.2