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Document constant behaviour for hashes

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Denton Liu 2016-08-29 15:12:35 -04:00
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docs/units-and-global-variables.rst
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@ -109,6 +109,10 @@ This means that the following are all identical::
If padding is needed, explicit type conversions can be used: ``sha3("\x00\x12")`` is the If padding is needed, explicit type conversions can be used: ``sha3("\x00\x12")`` is the
same as ``sha3(uint16(0x12))``. same as ``sha3(uint16(0x12))``.
Note that constants will packed using the minimum number of bytes required to store them.
This means that, for example, ``sha3(0) == sha3(uint8(0))`` and
``sha3(0x12345678) == sha3(uint32(0x12345678))``.
It might be that you run into Out-of-Gas for ``sha256``, ``ripemd160`` or ``ecrecover`` on a *private blockchain*. The reason for this is that those are implemented as so-called precompiled contracts and these contracts only really exist after they received the first message (although their contract code is hardcoded). Messages to non-existing contracts are more expensive and thus the execution runs into an Out-of-Gas error. A workaround for this problem is to first send e.g. 1 Wei to each of the contracts before you use them in your actual contracts. This is not an issue on the official or test net. It might be that you run into Out-of-Gas for ``sha256``, ``ripemd160`` or ``ecrecover`` on a *private blockchain*. The reason for this is that those are implemented as so-called precompiled contracts and these contracts only really exist after they received the first message (although their contract code is hardcoded). Messages to non-existing contracts are more expensive and thus the execution runs into an Out-of-Gas error. A workaround for this problem is to first send e.g. 1 Wei to each of the contracts before you use them in your actual contracts. This is not an issue on the official or test net.
.. _address_related: .. _address_related: