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Shortcut for 2^e #233

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Shortcut for 2^e #233

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f3d38f1
Shortcut for 2^e
AlexeyAkhunov May 5, 2020
cc4262d
Fix linter
AlexeyAkhunov May 6, 2020
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12 changes: 11 additions & 1 deletion lib/evmone/instructions.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -155,7 +155,17 @@ const instruction* op_exp(const instruction* instr, execution_state& state) noex
if ((state.gas_left -= additional_cost) < 0)
return state.exit(EVMC_OUT_OF_GAS);

exponent = intx::exp(base, exponent);
if (base == 2 && exponent < 256)
{
auto exp_bytes = as_bytes(exponent);
uint8_t bit_to_set = exp_bytes[0];
exp_bytes[0] = 0;
exp_bytes[bit_to_set >> 3] = uint8_t(uint8_t(1) << (bit_to_set & 7));
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Why not something like exponent = 2 << exponent; ?

@chfast would either of these solutions have a significant speed difference?

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Looks like at least in my benchmarks the 1 << exponent is the fastest (surprisingly). Full story in chfast/intx#146.

}
else
{
exponent = intx::exp(base, exponent);
}
return ++instr;
}

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