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Clarify packed encoding.

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chriseth 2018-08-08 21:47:40 +02:00 committed by GitHub
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docs/abi-spec.rst
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@ -565,14 +565,13 @@ Non-standard Packed Mode
Through ``abi.encodePacked()``, Solidity supports a non-standard packed mode where:
- no :ref:`function selector <abi_function_selector>` is encoded,
- types shorter than 32 bytes are neither zero padded nor sign extended and
- dynamic types are encoded in-place and without the length.
As an example encoding ``int1, bytes1, uint16, string`` with values ``-1, 0x42, 0x2424, "Hello, world!"`` results in ::
As an example encoding ``int8, bytes1, uint16, string`` with values ``-1, 0x42, 0x2424, "Hello, world!"`` results in ::
0xff42242448656c6c6f2c20776f726c6421
^^ int1(-1)
^^ int8(-1)
^^ bytes1(0x42)
^^^^ uint16(0x2424)
^^^^^^^^^^^^^^^^^^^^^^^^^^ string("Hello, world!") without a length field
@ -582,8 +581,7 @@ and dynamically-sized types like ``string``, ``bytes`` or ``uint[]`` are encoded
their length field. This means that the encoding is ambiguous as soon as there are two
dynamically-sized elements.
Note that constants will be packed using the minimum number of bytes required to store them.
This means that, for example, ``abi.encodePacked(0) == abi.encodePacked(uint8(0)) == hex"00"`` and
``abi.encodePacked(0x12345678) == abi.encodePacked(uint32(0x12345678)) == hex"12345678"``.
If padding is needed, explicit type conversions can be used: ``abi.encodePacked(uint16(0x12)) == hex"0012"``.
Since packed encoding is not used when calling functions, there is no special support
for prepending a function selector.