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Merge pull request #2871 from ethereum/fixedpointdocs

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Explain fixed point types in docs
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chriseth 2017-09-04 19:04:12 +02:00 committed by GitHub
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2 changed files with 24 additions and 14 deletions
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5
docs/frequently-asked-questions.rst
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@ -103,11 +103,6 @@ This is a limitation of the EVM and will be solved with the next protocol update
Returning variably-sized data as part of an external transaction or call is fine. Returning variably-sized data as part of an external transaction or call is fine.
How do you represent ``double``/``float`` in Solidity?
======================================================
This is not yet possible.
Is it possible to in-line initialize an array like so: ``string[] myarray = ["a", "b"];`` Is it possible to in-line initialize an array like so: ``string[] myarray = ["a", "b"];``
========================================================================================= =========================================================================================

33
docs/types.rst
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@ -70,6 +70,30 @@ sign extends. Shifting by a negative amount throws a runtime exception.
are going to be rounded towards zero (truncated). In other programming languages the shift right of 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). works like division with rounding down (towards negative infinity).
.. index:: ! ufixed, ! fixed, ! fixed point number
Fixed Point Numbers
-------------------
.. warning::
Fixed point numbers are not fully supported by Solidity yet. They can be declared, but
cannot be assigned to or from.
``fixed`` / ``ufixed``: Signed and unsigned fixed point number of various sizes. Keywords ``ufixedMxN`` and ``fixedMxN``, where ``M`` represent the number of bits taken by
the type and ``N`` represent how many decimal points are available. ``M`` must be divisible by 8 and goes from 8 to 256 bits. ``N`` must be between 0 and 80, inclusive.
``ufixed`` and ``fixed`` are aliases for ``ufixed128x19`` and ``fixed128x19``, respectively.
Operators:
* Comparisons: ``<=``, ``<``, ``==``, ``!=``, ``>=``, ``>`` (evaluate to ``bool``)
* Arithmetic operators: ``+``, ``-``, unary ``-``, unary ``+``, ``*``, ``/``, ``%`` (remainder)
.. note::
The main difference between floating point (``float`` and ``double`` in many languages, more precisely IEEE 754 numbers) and fixed point numbers is
that the number of bits used for the integer and the fractional part (the part after the decimal dot) is flexible in the former, while it is strictly
defined in the latter. Generally, in floating point almost the entire space is used to represent the number, while only a small number of bits define
where the decimal point is.
.. index:: address, balance, send, call, callcode, delegatecall, transfer .. index:: address, balance, send, call, callcode, delegatecall, transfer
.. _address: .. _address:
@ -203,15 +227,6 @@ As a rule of thumb, use ``bytes`` for arbitrary-length raw byte data and ``strin
for arbitrary-length string (UTF-8) data. If you can limit the length to a certain for arbitrary-length string (UTF-8) data. If you can limit the length to a certain
number of bytes, always use one of ``bytes1`` to ``bytes32`` because they are much cheaper. number of bytes, always use one of ``bytes1`` to ``bytes32`` because they are much cheaper.
.. index:: ! ufixed, ! fixed, ! fixed point number
Fixed Point Numbers
-------------------
.. warning::
Fixed point numbers are not fully supported by Solidity yet. They can be declared, but
cannot be assigned to or from.
.. index:: address, literal;address .. index:: address, literal;address
.. _address_literals: .. _address_literals: