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nit: move div by zero check from smod to i256_mod (bluealloy#1248)
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@jtraglia
jtraglia authored Mar 30, 2024
1 parent a201a2d commit 57825ff
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Showing 2 changed files with 106 additions and 38 deletions.
4 changes: 1 addition & 3 deletions crates/interpreter/src/instructions/arithmetic.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -48,9 +48,7 @@ pub fn rem<H: Host>(interpreter: &mut Interpreter, _host: &mut H) {
pub fn smod<H: Host>(interpreter: &mut Interpreter, _host: &mut H) {
gas!(interpreter, gas::LOW);
pop_top!(interpreter, op1, op2);
if *op2 != U256::ZERO {
*op2 = i256_mod(op1, *op2)
}
*op2 = i256_mod(op1, *op2)
}

pub fn addmod<H: Host>(interpreter: &mut Interpreter, _host: &mut H) {
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140 changes: 105 additions & 35 deletions crates/interpreter/src/instructions/i256.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -77,7 +77,7 @@ pub fn i256_div(mut first: U256, mut second: U256) -> U256 {
}

let first_sign = i256_sign_compl(&mut first);
if first_sign == Sign::Minus && first == MIN_NEGATIVE_VALUE && second == U256::from(1) {
if first == MIN_NEGATIVE_VALUE && second == U256::from(1) {
return two_compl(MIN_NEGATIVE_VALUE);
}

Expand Down Expand Up @@ -105,9 +105,11 @@ pub fn i256_mod(mut first: U256, mut second: U256) -> U256 {
return U256::ZERO;
}

let _ = i256_sign_compl(&mut second);
let second_sign = i256_sign_compl(&mut second);
if second_sign == Sign::Zero {
return U256::ZERO;
}

// necessary overflow checks are done above, perform the operation
let mut r = first % second;

// set sign bit to zero
Expand All @@ -125,6 +127,58 @@ mod tests {
use super::*;
use core::num::Wrapping;

const ZERO: U256 = U256::ZERO;
const ONE: U256 = U256::from_limbs([
0x0000000000000001,
0x0000000000000000,
0x0000000000000000,
0x0000000000000000,
]);
const TWO: U256 = U256::from_limbs([
0x0000000000000002,
0x0000000000000000,
0x0000000000000000,
0x0000000000000000,
]);
const THREE: U256 = U256::from_limbs([
0x0000000000000003,
0x0000000000000000,
0x0000000000000000,
0x0000000000000000,
]);
const FOUR: U256 = U256::from_limbs([
0x0000000000000004,
0x0000000000000000,
0x0000000000000000,
0x0000000000000000,
]);

const NEG_ONE: U256 = U256::from_limbs([
0xffffffffffffffff,
0xffffffffffffffff,
0xffffffffffffffff,
0xffffffffffffffff,
]);
const NEG_TWO: U256 = U256::from_limbs([
0xfffffffffffffffe,
0xffffffffffffffff,
0xffffffffffffffff,
0xffffffffffffffff,
]);
const NEG_THREE: U256 = U256::from_limbs([
0xfffffffffffffffd,
0xffffffffffffffff,
0xffffffffffffffff,
0xffffffffffffffff,
]);

const I256_MAX: U256 = U256::from_limbs([
0xffffffffffffffff,
0xffffffffffffffff,
0xffffffffffffffff,
0x7fffffffffffffff,
]);

#[test]
fn div_i256() {
// Sanity checks based on i8. Notice that we need to use `Wrapping` here because
Expand All @@ -133,70 +187,86 @@ mod tests {
assert_eq!(i8::MAX / -1, -i8::MAX);

// Now the same calculations based on i256
let one = U256::from(1);
let one_hundred = U256::from(100);
let fifty = U256::from(50);
let two = U256::from(2);
let neg_one_hundred = U256::from(100);
let minus_one = U256::from(1);
let max_value = U256::from(2).pow(U256::from(255)) - U256::from(1);
let neg_max_value = U256::from(2).pow(U256::from(255)) - U256::from(1);

assert_eq!(i256_div(MIN_NEGATIVE_VALUE, minus_one), MIN_NEGATIVE_VALUE);
assert_eq!(i256_div(MIN_NEGATIVE_VALUE, one), MIN_NEGATIVE_VALUE);
assert_eq!(i256_div(max_value, one), max_value);
assert_eq!(i256_div(max_value, minus_one), neg_max_value);
assert_eq!(i256_div(one_hundred, minus_one), neg_one_hundred);
assert_eq!(i256_div(one_hundred, two), fifty);
let one_hundred = U256::from(100);

assert_eq!(i256_div(MIN_NEGATIVE_VALUE, NEG_ONE), MIN_NEGATIVE_VALUE);
assert_eq!(i256_div(MIN_NEGATIVE_VALUE, ONE), MIN_NEGATIVE_VALUE);
assert_eq!(i256_div(I256_MAX, ONE), I256_MAX);
assert_eq!(i256_div(I256_MAX, NEG_ONE), NEG_ONE * I256_MAX);
assert_eq!(i256_div(one_hundred, NEG_ONE), NEG_ONE * one_hundred);
assert_eq!(i256_div(one_hundred, TWO), fifty);
}
#[test]
fn test_i256_sign() {
assert_eq!(i256_sign(&U256::ZERO), Sign::Zero);
assert_eq!(i256_sign(&U256::from(1)), Sign::Plus);
assert_eq!(i256_sign(&ZERO), Sign::Zero);
assert_eq!(i256_sign(&ONE), Sign::Plus);
assert_eq!(i256_sign(&MIN_NEGATIVE_VALUE), Sign::Minus);
}

#[test]
fn test_i256_sign_compl() {
let mut positive = U256::from(1);
let mut zero = ZERO;
let mut positive = ONE;
let mut negative = MIN_NEGATIVE_VALUE;
assert_eq!(i256_sign_compl(&mut zero), Sign::Zero);
assert_eq!(i256_sign_compl(&mut positive), Sign::Plus);
assert_eq!(i256_sign_compl(&mut negative), Sign::Minus);
}

#[test]
fn test_two_compl() {
let value = U256::from(1);
assert_eq!(two_compl(value), U256::MAX);
assert_eq!(two_compl(ZERO), ZERO);
assert_eq!(two_compl(ONE), NEG_ONE);
assert_eq!(two_compl(NEG_ONE), ONE);
assert_eq!(two_compl(TWO), NEG_TWO);
assert_eq!(two_compl(NEG_TWO), TWO);

// Two's complement of the min value is itself.
assert_eq!(two_compl(MIN_NEGATIVE_VALUE), MIN_NEGATIVE_VALUE);
}

#[test]
fn test_two_compl_mut() {
let mut value = U256::from(1);
let mut value = ONE;
two_compl_mut(&mut value);
assert_eq!(value, U256::MAX);
assert_eq!(value, NEG_ONE);
}

#[test]
fn test_i256_cmp() {
assert_eq!(i256_cmp(&U256::from(1), &U256::from(2)), Ordering::Less);
assert_eq!(i256_cmp(&U256::from(2), &U256::from(2)), Ordering::Equal);
assert_eq!(i256_cmp(&U256::from(3), &U256::from(2)), Ordering::Greater);
assert_eq!(i256_cmp(&ONE, &TWO), Ordering::Less);
assert_eq!(i256_cmp(&TWO, &TWO), Ordering::Equal);
assert_eq!(i256_cmp(&THREE, &TWO), Ordering::Greater);
assert_eq!(i256_cmp(&NEG_ONE, &NEG_ONE), Ordering::Equal);
assert_eq!(i256_cmp(&NEG_ONE, &NEG_TWO), Ordering::Greater);
assert_eq!(i256_cmp(&NEG_ONE, &ZERO), Ordering::Less);
assert_eq!(i256_cmp(&NEG_TWO, &TWO), Ordering::Less);
}

#[test]
fn test_i256_div() {
let one = U256::from(1);
let two = U256::from(2);
assert_eq!(i256_div(MIN_NEGATIVE_VALUE, one), MIN_NEGATIVE_VALUE);
assert_eq!(i256_div(U256::from(4), two), U256::from(2));
assert_eq!(i256_div(ONE, ZERO), ZERO);
assert_eq!(i256_div(ZERO, ONE), ZERO);
assert_eq!(i256_div(ZERO, NEG_ONE), ZERO);
assert_eq!(i256_div(MIN_NEGATIVE_VALUE, ONE), MIN_NEGATIVE_VALUE);
assert_eq!(i256_div(FOUR, TWO), TWO);
assert_eq!(i256_div(MIN_NEGATIVE_VALUE, MIN_NEGATIVE_VALUE), ONE);
assert_eq!(i256_div(TWO, NEG_ONE), NEG_TWO);
assert_eq!(i256_div(NEG_TWO, NEG_ONE), TWO);
}

#[test]
fn test_i256_mod() {
let one = U256::from(1);
let two = U256::from(2);
assert_eq!(i256_mod(U256::from(4), two), U256::ZERO);
assert_eq!(i256_mod(U256::from(3), two), one);
assert_eq!(i256_mod(ZERO, ONE), ZERO);
assert_eq!(i256_mod(ONE, ZERO), ZERO);
assert_eq!(i256_mod(FOUR, TWO), ZERO);
assert_eq!(i256_mod(THREE, TWO), ONE);
assert_eq!(i256_mod(MIN_NEGATIVE_VALUE, ONE), ZERO);
assert_eq!(i256_mod(TWO, TWO), ZERO);
assert_eq!(i256_mod(TWO, THREE), TWO);
assert_eq!(i256_mod(NEG_TWO, THREE), NEG_TWO);
assert_eq!(i256_mod(TWO, NEG_THREE), TWO);
assert_eq!(i256_mod(NEG_TWO, NEG_THREE), NEG_TWO);
}
}

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