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WIP: optimisation of byte opcode #1303

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allnil wants to merge 2 commits into from
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WIP: optimisation of byte opcode #1303

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edd1201
feat: play with byte opcode
allnil Apr 12, 2024
4abf946
chore: make it clean in bytes (almost)
allnil Apr 12, 2024
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20 changes: 17 additions & 3 deletions crates/interpreter/src/instructions/bitwise.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -71,10 +71,24 @@ pub fn byte<H: Host + ?Sized>(interpreter: &mut Interpreter, _host: &mut H) {
gas!(interpreter, gas::VERYLOW);
pop_top!(interpreter, op1, op2);

let o1 = as_usize_saturated!(op1);
let o1 = as_u64_saturated!(op1);
//const MAX_BYTE: u64 = 31;

*op2 = if o1 < 32 {
// `31 - o1` because `byte` returns LE, while we want BE
U256::from(op2.byte(31 - o1))
/*
number := z[4-1-number/8]
offset := (n[0] & 0x7) << 3 // 8*(n.d % 8)
z[0] = (number & (0xff00000000000000 >> offset)) >> (56 - offset)
z[3], z[2], z[1] = 0, 0, 0
return z
*/
// Calculate which byte to extract
// Calculate bit position for the byte extraction
let byte_index = (o1 * 8) as u64;
let shift_amount = 248 - byte_index;

// Shift the value down to the least significant byte and mask off the rest
(*op2 >> shift_amount) & U256::from(0xFF)
} else {
U256::ZERO
};
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