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Ropsten transactions are confirmed by miners on that POW network.
Rinkeby transactions are confirmed by specific authorized nodes run by the the Geth team. The Ethereum Foundation, Infura, AKASHA and others might also be involved.
Non-validator nodes are run by others in the ethereum space such as PegaSys, Funfair, etc. You can see the list of Rinkeby ...
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Tested the following code:
pragma solidity ^0.5.0;
contract Test {
function iadd(int a, int b) public pure returns (int) {return a + b;}
function uadd(uint a, uint b) public pure returns (uint) {return a + b;}
}
Using solc 0.5.13:
solc --bin --abi --asm --output-dir=binaries Test.sol ...
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They are approximately the same.
Your fixed-size array lays out a very large address space where every possible address equivalent has a slot. That's logically equivalent to what mapping does, although laid out differently (See Ismael's comment below) and slight different in gas cost as a result.
I would incline to the mapping for readability. Solidity ...
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UPDATE:
The answer below refers to the difference between:
a mapping(address => uint)
an array of struct {address key; uint value;} elements
Which is not what's being asked here.
I'm leaving it here because I feel that it still contributes something in the context of this question...
I hope that this table answers your question:
|----------------|---...
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Ok, add(_bytes, 0xc) adds 12 (0x0c) to the address of _bytes.
add(add(_bytes, 0xc), _start) adds 12 and _start to the address of _bytes.
mload(add(add(_bytes, 0xc), _start)) loads onto the stack 32 bytes starting from the address of _bytes increased by 12 and _start. In other words, it loads bytes at offsets (12 + _start) ... (43 + _start) counting from ...
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