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