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Optimize DIV for some common divisors #2327

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Sep 27, 2016
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Optimize DIV for some common divisors #2327

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25 changes: 24 additions & 1 deletion ethcore/src/evm/interpreter/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -53,6 +53,17 @@ fn color(instruction: Instruction, name: &'static str) -> String {
type CodePosition = usize;
type ProgramCounter = usize;

const ONE: U256 = U256([1, 0, 0, 0]);
const TWO: U256 = U256([2, 0, 0, 0]);
const TWO_POW_5: U256 = U256([0x20, 0, 0, 0]);
const TWO_POW_8: U256 = U256([0x100, 0, 0, 0]);
const TWO_POW_16: U256 = U256([0x10000, 0, 0, 0]);
const TWO_POW_24: U256 = U256([0x1000000, 0, 0, 0]);
const TWO_POW_64: U256 = U256([0, 0x1, 0, 0]); // 0x1 00000000 00000000
const TWO_POW_96: U256 = U256([0, 0x100000000, 0, 0]); //0x1 00000000 00000000 00000000
const TWO_POW_224: U256 = U256([0, 0, 0, 0x100000000]); //0x1 00000000 00000000 00000000 00000000 00000000 00000000 00000000
const TWO_POW_248: U256 = U256([0, 0, 0, 0x100000000000000]); //0x1 00000000 00000000 00000000 00000000 00000000 00000000 00000000 000000

/// Abstraction over raw vector of Bytes. Easier state management of PC.
struct CodeReader<'a> {
position: ProgramCounter,
Expand Down Expand Up @@ -599,7 +610,19 @@ impl<Cost: CostType> Interpreter<Cost> {
let a = stack.pop_back();
let b = stack.pop_back();
stack.push(if !self.is_zero(&b) {
a.overflowing_div(b).0
match b {
ONE => a,
TWO => a >> 1,
TWO_POW_5 => a >> 5,
TWO_POW_8 => a >> 8,
TWO_POW_16 => a >> 16,
TWO_POW_24 => a >> 24,
TWO_POW_64 => a >> 64,
TWO_POW_96 => a >> 96,
TWO_POW_224 => a >> 224,
TWO_POW_248 => a >> 248,
_ => a.overflowing_div(b).0,
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couldn't these be put into the implementation of div itself for U256?

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I think it's better here - it's for evm's specific use cases. Uint is supposed to be general purpose library I don't think it suits well there. Probably would be better to use a different division algorithm there in additon.

}
} else {
U256::zero()
});
Expand Down