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use bigint::{Gas, U256};
use std::rc::Rc;
use evm::errors::{NotSupportedError, OnChainError, RuntimeError};
use evm::Precompiled;
pub static MODEXP_PRECOMPILED: ModexpPrecompiled = ModexpPrecompiled;
pub struct ModexpPrecompiled;
impl Precompiled for ModexpPrecompiled {
fn gas_and_step(&self, data: &[u8], gas_limit: Gas) -> Result<(Gas, Rc<Vec<u8>>), RuntimeError> {
use num_bigint::BigUint;
use std::cmp;
fn adjusted_exponent_length(exponent_length: U256, base_length: U256, data: &[u8]) -> U256 {
let mut exp32_arr = Vec::new();
for i in 0..32 {
if U256::from(96) + base_length + U256::from(i) >= U256::from(data.len()) {
exp32_arr.push(0u8);
} else {
let base_length_usize: usize = base_length.as_usize();
let data_i: usize = 96 + base_length_usize + i;
exp32_arr.push(data[data_i]);
}
}
let exp32 = U256::from(exp32_arr.as_slice());
if exponent_length <= U256::from(32) && exp32 == U256::zero() {
U256::zero()
} else if exponent_length <= U256::from(32) {
U256::from(exp32.bits())
} else {
U256::from(8) * (exponent_length - U256::from(32)) + U256::from(exp32.bits())
}
}
fn mult_complexity(x: U256) -> Result<U256, RuntimeError> {
if x <= U256::from(64) {
Ok(x * x)
} else if x <= U256::from(1024) {
Ok(x * x / U256::from(4) + U256::from(96) * x - U256::from(3072))
} else {
let (sqr, o) = x.overflowing_mul(x);
if o {
Err(RuntimeError::OnChain(OnChainError::EmptyGas))
} else {
Ok(sqr / U256::from(16) + U256::from(480) * x - U256::from(199680))
}
}
}
let mut data: Vec<u8> = data.into();
while data.len() < 32 * 3 {
data.push(0);
}
let base_length = U256::from(&data[0..32]);
let exponent_length = U256::from(&data[32..64]);
let modulus_length = U256::from(&data[64..96]);
let op1 = mult_complexity(cmp::max(modulus_length, base_length))?;
let ael = adjusted_exponent_length(exponent_length, base_length, &data);
let op2 = cmp::max(ael, U256::from(1)) / U256::from(20);
let (r, o) = op1.overflowing_mul(op2);
if o {
return Err(RuntimeError::OnChain(OnChainError::EmptyGas));
}
let gas: Gas = r.into();
if gas > gas_limit {
return Err(RuntimeError::OnChain(OnChainError::EmptyGas));
}
if base_length > U256::from(usize::max_value())
|| exponent_length > U256::from(usize::max_value())
|| modulus_length > U256::from(usize::max_value())
{
return Err(RuntimeError::NotSupported(NotSupportedError::MemoryIndexNotSupported));
}
let base_length: usize = base_length.as_usize();
let exponent_length: usize = exponent_length.as_usize();
let modulus_length: usize = modulus_length.as_usize();
let mut base_arr = Vec::new();
let mut exponent_arr = Vec::new();
let mut modulus_arr = Vec::new();
for i in 0..base_length {
if 96 + i >= data.len() {
base_arr.push(0u8);
} else {
base_arr.push(data[96 + i]);
}
}
for i in 0..exponent_length {
if 96 + base_length + i >= data.len() {
exponent_arr.push(0u8);
} else {
exponent_arr.push(data[96 + base_length + i]);
}
}
for i in 0..modulus_length {
if 96 + base_length + exponent_length + i >= data.len() {
modulus_arr.push(0u8);
} else {
modulus_arr.push(data[96 + base_length + exponent_length + i]);
}
}
let base = BigUint::from_bytes_be(&base_arr);
let exponent = BigUint::from_bytes_be(&exponent_arr);
let modulus = BigUint::from_bytes_be(&modulus_arr);
let mut result = base.modpow(&exponent, &modulus).to_bytes_be();
assert!(result.len() <= modulus_length);
while result.len() < modulus_length {
result.insert(0, 0u8);
}
Ok((gas, Rc::new(result)))
}
}
#[cfg(test)]
mod tests {
use crate::*;
use hexutil::*;
#[test]
fn spec_test1() {
let input = read_hex("00000000000000000000000000000000000000000000000000000000000000010000000000000000000000000000000000000000000000000000000000000020000000000000000000000000000000000000000000000000000000000000002003fffffffffffffffffffffffffffffffffffffffffffffffffffffffefffffc2efffffffffffffffffffffffffffffffffffffffffffffffffffffffefffffc2f").unwrap();
let (_, output) = MODEXP_PRECOMPILED
.gas_and_step(&input, Gas::from(10000000usize))
.unwrap();
let expected = read_hex("0000000000000000000000000000000000000000000000000000000000000001").unwrap();
assert_eq!(expected, Rc::try_unwrap(output).unwrap());
}
#[test]
fn spec_test2() {
let input = read_hex("000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000200000000000000000000000000000000000000000000000000000000000000020fffffffffffffffffffffffffffffffffffffffffffffffffffffffefffffc2efffffffffffffffffffffffffffffffffffffffffffffffffffffffefffffc2f").unwrap();
let (_, output) = MODEXP_PRECOMPILED
.gas_and_step(&input, Gas::from(10000000usize))
.unwrap();
let expected = read_hex("0000000000000000000000000000000000000000000000000000000000000000").unwrap();
assert_eq!(expected, Rc::try_unwrap(output).unwrap());
}
#[test]
fn spec_test3() {
let input = read_hex("00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000020fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffefffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffd").unwrap();
match MODEXP_PRECOMPILED.gas_and_step(&input, Gas::from(10000000usize)) {
Ok(_) => panic!(),
Err(_) => (),
}
}
#[test]
fn spec_test4() {
let input = read_hex("00000000000000000000000000000000000000000000000000000000000000010000000000000000000000000000000000000000000000000000000000000002000000000000000000000000000000000000000000000000000000000000002003ffff800000000000000000000000000000000000000000000000000000000000000007").unwrap();
let (_, output) = MODEXP_PRECOMPILED
.gas_and_step(&input, Gas::from(10000000usize))
.unwrap();
let expected = read_hex("3b01b01ac41f2d6e917c6d6a221ce793802469026d9ab7578fa2e79e4da6aaab").unwrap();
assert_eq!(expected, Rc::try_unwrap(output).unwrap());
}
#[test]
fn sepc_test5() {
let input = read_hex("00000000000000000000000000000000000000000000000000000000000000010000000000000000000000000000000000000000000000000000000000000002000000000000000000000000000000000000000000000000000000000000002003ffff80").unwrap();
let (_, output) = MODEXP_PRECOMPILED
.gas_and_step(&input, Gas::from(10000000usize))
.unwrap();
let expected = read_hex("3b01b01ac41f2d6e917c6d6a221ce793802469026d9ab7578fa2e79e4da6aaab").unwrap();
assert_eq!(expected, Rc::try_unwrap(output).unwrap());
}
}