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Merge pull request #3231 from ethereum/chriseth-patch-2

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More explanation about the packed encoding.
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Alex Beregszaszi 2017-11-22 12:30:04 +00:00 committed by GitHub
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docs/abi-spec.rst
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@ -451,13 +451,18 @@ Non-standard Packed Mode
Solidity supports a non-standard packed mode where: Solidity supports a non-standard packed mode where:
- no :ref:`function selector <abi_function_selector>` is encoded, - no :ref:`function selector <abi_function_selector>` is encoded,
- short types are not zero padded and - types shorter than 32 bytes are neither zero padded nor sign extended and
- dynamic types are encoded in-place and without the length. - dynamic types are encoded in-place and without the length.
As an example encoding ``uint1, bytes1, uint8, string`` with values ``1, 0x42, 0x2424, "Hello, world!"`` results in :: As an example encoding ``int1, bytes1, uint16, string`` with values ``-1, 0x42, 0x2424, "Hello, world!"`` results in ::
0x0142242448656c6c6f2c20776f726c6421 0xff42242448656c6c6f2c20776f726c6421
^^ uint1(1) ^^ int1(-1)
^^ bytes1(0x42) ^^ bytes1(0x42)
^^^^ uint8(0x2424) ^^^^ uint16(0x2424)
^^^^^^^^^^^^^^^^^^^^^^^^^^ string("Hello, world!") without a length field ^^^^^^^^^^^^^^^^^^^^^^^^^^ string("Hello, world!") without a length field
More specifically, each statically-sized type takes as many bytes as its range has
and dynamically-sized types like ``string``, ``bytes`` or ``uint[]`` are encoded without
their length field. This means that the encoding is ambiguous as soon as there are two
dynamically-sized elements.