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Use proper SAR for signed right shifts and emulate on pre-constantinople.

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Daniel Kirchner
2018-06-12 09:32:19 +01:00
committed by Alex Beregszaszi
parent 8999a2f375
commit f33dc92cbd
5 changed files with 152 additions and 70 deletions
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docs/types.rst
+6 -7
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@@ -60,15 +60,14 @@ operators are :ref:`literals<rational_literals>` (or literal expressions).
Division by zero and modulus with zero throws a runtime exception.
The result of a shift operation is the type of the left operand. The
expression ``x << y`` is equivalent to ``x * 2**y``, and ``x >> y`` is
equivalent to ``x / 2**y``. This means that shifting negative numbers
sign extends. Shifting by a negative amount throws a runtime exception.
expression ``x << y`` is equivalent to ``x * 2**y``, and, for positive integers,
``x >> y`` is equivalent to ``x / 2**y``. For negative ``x``, ``x >> y``
is equivalent to dividing by a power of ``2`` while rounding down (towards negative infinity).
Shifting by a negative amount throws a runtime exception.
.. warning::
The results produced by shift right of negative values of signed integer types is different from those produced
by other programming languages. In Solidity, shift right maps to division so the shifted negative values
are going to be rounded towards zero (truncated). In other programming languages the shift right of negative values
works like division with rounding down (towards negative infinity).
Before version ``0.5.0`` a right shift ``x >> y`` for negative ``x`` was equivalent to ``x / 2**y``,
i.e. right shifts used rounding towards zero instead of rounding towards negative infinity.
.. index:: ! ufixed, ! fixed, ! fixed point number