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Merge pull request #4200 from biboran/3961

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#3961 - added an example of two-dimensional array encoding
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chriseth 2018-06-21 14:09:53 +02:00 committed by GitHub
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@ -277,6 +277,106 @@ All together, the encoding is (newline after function selector and each 32-bytes
000000000000000000000000000000000000000000000000000000000000000d
48656c6c6f2c20776f726c642100000000000000000000000000000000000000
Let us apply the same principle to encode the data for a function with a signature ``g(uint[][],string[])`` with values ``([[1, 2], [3]], ["one", "two", "three"])`` but start from the most atomic parts of the encoding:
First we encode the length and data of the first embeded dynamic array ``[1, 2]`` of the first root array ``[[1, 2], [3]]``:
- ``0x0000000000000000000000000000000000000000000000000000000000000002`` (number of elements in the first array, 2; the elements themselves are ``1`` and ``2``)
- ``0x0000000000000000000000000000000000000000000000000000000000000001`` (first element)
- ``0x0000000000000000000000000000000000000000000000000000000000000002`` (second element)
Then we encode the length and data of the second embeded dynamic array ``[3]`` of the first root array ``[[1, 2], [3]]``:
- ``0x0000000000000000000000000000000000000000000000000000000000000001`` (number of elements in the second array, 1; the element is ``3``)
- ``0x0000000000000000000000000000000000000000000000000000000000000003`` (first element)
Then we need to find the offsets ``a`` and ``b`` for their respective dynamic arrays ``[1, 2]`` and ``[3]``. To calculate the offsets we can take a look at the encoded data of the first root array ``[[1, 2], [3]]`` enumerating each line in the encoding:
::
0 - a - offset of [1, 2]
1 - b - offset of [3]
2 - 0000000000000000000000000000000000000000000000000000000000000002 - count for [1, 2]
3 - 0000000000000000000000000000000000000000000000000000000000000001 - encoding of 1
4 - 0000000000000000000000000000000000000000000000000000000000000002 - encoding of 2
5 - 0000000000000000000000000000000000000000000000000000000000000001 - count for [3]
6 - 0000000000000000000000000000000000000000000000000000000000000003 - encoding of 3
Offset ``a`` points to the start of the content of the array ``[1, 2]`` which is line 2 (64 bytes); thus ``a = 0x0000000000000000000000000000000000000000000000000000000000000040``.
Offset ``b`` points to the start of the content of the array ``[3]`` which is line 5 (160 bytes); thus ``b = 0x00000000000000000000000000000000000000000000000000000000000000a0``.
Then we encode the embeded strings of the second root array:
- ``0x0000000000000000000000000000000000000000000000000000000000000003`` (number of characters in word ``"one"``)
- ``0x6f6e650000000000000000000000000000000000000000000000000000000000`` (utf8 representation of word ``"one"``)
- ``0x0000000000000000000000000000000000000000000000000000000000000003`` (number of characters in word ``"two"``)
- ``0x74776f0000000000000000000000000000000000000000000000000000000000`` (utf8 representation of word ``"two"``)
- ``0x0000000000000000000000000000000000000000000000000000000000000005`` (number of characters in word ``"three"``)
- ``0x7468726565000000000000000000000000000000000000000000000000000000`` (utf8 representation of word ``"three"``)
In parallel to the first root array, since strings are dynamic elements we need to find their offsets ``c``, ``d`` and ``e``:
::
0 - c - offset for "one"
1 - d - offset for "two"
2 - e - offset for "three"
3 - 0000000000000000000000000000000000000000000000000000000000000003 - count for "one"
4 - 6f6e650000000000000000000000000000000000000000000000000000000000 - encoding of "one"
5 - 0000000000000000000000000000000000000000000000000000000000000003 - count for "two"
6 - 74776f0000000000000000000000000000000000000000000000000000000000 - encoding of "two"
7 - 0000000000000000000000000000000000000000000000000000000000000005 - count for "three"
8 - 7468726565000000000000000000000000000000000000000000000000000000 - encoding of "three"
Offset ``c`` points to the start of the content of the string ``"one"`` which is line 3 (96 bytes); thus ``c = 0x0000000000000000000000000000000000000000000000000000000000000060``.
Offset ``d`` points to the start of the content of the string ``"two"`` which is line 5 (160 bytes); thus ``d = 0x00000000000000000000000000000000000000000000000000000000000000a0``.
Offset ``e`` points to the start of the content of the string ``"three"`` which is line 7 (224 bytes); thus ``e = 0x00000000000000000000000000000000000000000000000000000000000000e0``.
Note that the encodings of the embeded elements of the root arrays are not dependent on each other and have the same encodings for a fuction with a signature ``g(string[],uint[][])``.
Then we encode the length of the first root array:
- ``0x0000000000000000000000000000000000000000000000000000000000000002`` (number of elements in the first root array, 2; the elements themselves are ``[1, 2]`` and ``[3]``)
Then we encode the length of the second root array:
- ``0x0000000000000000000000000000000000000000000000000000000000000003`` (number of strings in the second root array, 3; the strings themselves are ``"one"``, ``"two"`` and ``"three"``)
Finally we find the offsets ``f`` and ``g`` for their respective root dynamic arrays ``[[1, 2], [3]]`` and ``["one", "two", "three"]``, and assemble parts in the correct order:
::
0x2289b18c - function signature
0 - f - offset of [[1, 2], [3]]
1 - g - offset of ["one", "two", "three"]
2 - 0000000000000000000000000000000000000000000000000000000000000002 - count for [[1, 2], [3]]
3 - 0000000000000000000000000000000000000000000000000000000000000040 - offset of [1, 2]
4 - 00000000000000000000000000000000000000000000000000000000000000a0 - offset of [3]
5 - 0000000000000000000000000000000000000000000000000000000000000002 - count for [1, 2]
6 - 0000000000000000000000000000000000000000000000000000000000000001 - encoding of 1
7 - 0000000000000000000000000000000000000000000000000000000000000002 - encoding of 2
8 - 0000000000000000000000000000000000000000000000000000000000000001 - count for [3]
9 - 0000000000000000000000000000000000000000000000000000000000000003 - encoding of 3
10 - 0000000000000000000000000000000000000000000000000000000000000003 - count for ["one", "two", "three"]
11 - 0000000000000000000000000000000000000000000000000000000000000060 - offset for "one"
12 - 00000000000000000000000000000000000000000000000000000000000000a0 - offset for "two"
13 - 00000000000000000000000000000000000000000000000000000000000000e0 - offset for "three"
14 - 0000000000000000000000000000000000000000000000000000000000000003 - count for "one"
15 - 6f6e650000000000000000000000000000000000000000000000000000000000 - encoding of "one"
16 - 0000000000000000000000000000000000000000000000000000000000000003 - count for "two"
17 - 74776f0000000000000000000000000000000000000000000000000000000000 - encoding of "two"
18 - 0000000000000000000000000000000000000000000000000000000000000005 - count for "three"
19 - 7468726565000000000000000000000000000000000000000000000000000000 - encoding of "three"
Offset ``f`` points to the start of the content of the array ``[[1, 2], [3]]`` which is line 2 (64 bytes); thus ``f = 0x0000000000000000000000000000000000000000000000000000000000000040``.
Offset ``g`` points to the start of the content of the array ``["one", "two", "three"]`` which is line 10 (320 bytes); thus ``g = 0x0000000000000000000000000000000000000000000000000000000000000140``.
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