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Example8.yul
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Example8.yul
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object "FunctionSelectorExample" {
code {
// Deploy the contract
// Copy the runtime code to memory starting at position 0
datacopy(0, dataoffset("Runtime"), datasize("Runtime"))
// Return the runtime code to be executed
return(0, datasize("Runtime"))
}
object "Runtime" {
code {
// Function selector logic
switch getSelector()
// Case for function selector of "get()"
case 0x6d4ce63c /* "get()" */ {
// Load the value from storage at position 0 into memory at position 0
mstore(0, sload(0))
// Return the value from memory at position 0 with length 32 bytes
return(0, 32)
}
// Case for function selector of "increment()"
case 0x371303c0 /* "increment()" */ {
// Load the value from storage at position 0, increment it by 1, and store it back
sstore(0, add(sload(0), 1))
// Stop execution
stop()
}
// Case for function selector of "decrement()"
case 0xb3bcfa82 /* "decrement()" */ {
// Load the value from storage at position 0, decrement it by 1, and store it back
sstore(0, sub(sload(0), 1))
// Stop execution
stop()
}
// Default case if no function selector matches
default {
// Revert the transaction with no data
revert(0, 0)
}
// Helper function to get the function selector from the calldata
function getSelector() -> selector {
// Load the first 32 bytes of calldata and right-shift to get the first 4 bytes (function selector)
selector := div(calldataload(0), 0x100000000000000000000000000000000000000000000000000000000)
// Explanation for the div operation (it might look weird since we don't "bit shift" in a more classical sense:
// The division operation div(calldataload(0), 0x100000000000000000000000000000000000000000000000000000000)
// effectively right-shifts the 256-bit value by 224 bits (28 bytes).
// The number 0x100000000000000000000000000000000000000000000000000000000 in hexadecimal is 2^224.
// Dividing by 2^224 discards the rightmost 224 bits, leaving only the leftmost 32 bits (4 bytes),
// which is the function selector.
}
}
}
}