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.. _module-pw_varint:
---------
pw_varint
---------
The ``pw_varint`` module provides functions for encoding and decoding variable
length integers, or varints. For smaller values, varints require less memory
than a fixed-size encoding. For example, a 32-bit (4-byte) integer requires 1--5
bytes when varint-encoded.
`Protocol Buffers <https://developers.google.com/protocol-buffers/docs/encoding#varints>`_
use a variable-length encoding for integers.
Compatibility
=============
* C
* C++14 (with :doc:`../pw_polyfill/docs`)
API
===
.. cpp:function:: size_t EncodedSize(uint64_t integer)
Returns the size of an integer when encoded as a varint. Works on both signed
and unsigned integers.
.. cpp:function:: size_t ZigZagEncodedSize(int64_t integer)
Returns the size of a signed integer when ZigZag encoded as a varint.
.. cpp:function:: uint64_t MaxValueInBytes(size_t bytes)
Returns the maximum integer value that can be encoded as a varint into the
specified number of bytes.
Stream API
----------
.. cpp:function:: StatusWithSize Read(stream::Reader& reader, int64_t* output)
.. cpp:function:: StatusWithSize Read(stream::Reader& reader, uint64_t* output)
Decoders a varint from the current position of a stream. If reading into a
signed integer, the value is ZigZag decoded.
Returns the number of bytes read from the stream, places the value in `output`,
if successful. Returns `OutOfRange` if the varint does not fit in to the type,
or if the input is exhausted before the number terminates.
Reads a maximum of 10 bytes.
Dependencies
============
* ``pw_span``
Zephyr
======
To enable ``pw_varint`` for Zephyr add ``CONFIG_PIGWEED_VARINT=y`` to the
project's configuration.
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