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Detecting overflows in shl

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This commit is contained in:
Tomusdrw 2016-01-15 14:40:54 +01:00
parent b8a2a16e83
commit 0ea9e13210
1 changed files with 128 additions and 43 deletions
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167
src/uint.rs
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@ -35,8 +35,24 @@ macro_rules! impl_map_from {
} }
} }
macro_rules! overflowing {
($op: expr, $overflow: expr) => (
{
let (overflow_x, overflow_overflow) = $op;
$overflow |= overflow_overflow;
overflow_x
}
);
($op: expr) => (
{
let (overflow_x, _overflow_overflow) = $op;
overflow_x
}
);
}
macro_rules! panic_on_overflow { macro_rules! panic_on_overflow {
($name:expr) => { ($name: expr) => {
if $name { if $name {
panic!("arithmetic operation overflow") panic!("arithmetic operation overflow")
} }
@ -223,22 +239,16 @@ macro_rules! construct_uint {
while n > u_one { while n > u_one {
if is_even(&n) { if is_even(&n) {
let (c, mul_overflow) = x.overflowing_mul(x); x = overflowing!(x.overflowing_mul(x), overflow);
x = c;
overflow |= mul_overflow;
n = n / u_two; n = n / u_two;
} else { } else {
let (new_y, y_overflow) = x.overflowing_mul(y); y = overflowing!(x.overflowing_mul(y), overflow);
let (new_x, x_overflow) = x.overflowing_mul(x); x = overflowing!(x.overflowing_mul(x), overflow);
x = new_x;
y = new_y;
overflow |= y_overflow | x_overflow;
n = (n - u_one) / u_two; n = (n - u_one) / u_two;
} }
} }
let (res, mul_overflow) = x.overflowing_mul(y); let res = overflowing!(x.overflowing_mul(y), overflow);
(res, mul_overflow | overflow) (res, overflow)
} }
/// Multiplication by u32 /// Multiplication by u32
@ -283,8 +293,11 @@ macro_rules! construct_uint {
overflow = true overflow = true
} }
} }
let (result, add_overflow) = $name(ret).overflowing_add($name(carry)); let result = overflowing!(
(result, add_overflow || overflow) $name(ret).overflowing_add($name(carry)),
overflow
);
(result, overflow)
} }
} }
@ -383,21 +396,21 @@ macro_rules! construct_uint {
carry[i + 1] = 1; carry[i + 1] = 1;
b_carry = true; b_carry = true;
} else { } else {
overflow = true overflow = true;
} }
} }
} }
if b_carry { if b_carry {
let (ret, add_overflow) = $name(ret).overflowing_add($name(carry)); let ret = overflowing!($name(ret).overflowing_add($name(carry)), overflow);
(ret, add_overflow || overflow) (ret, overflow)
} else { } else {
($name(ret), overflow) ($name(ret), overflow)
} }
} }
fn overflowing_sub(self, other: $name) -> ($name, bool) { fn overflowing_sub(self, other: $name) -> ($name, bool) {
let (res, _overflow) = (!other).overflowing_add(From::from(1u64)); let res = overflowing!((!other).overflowing_add(From::from(1u64)));
let (res, _overflow) = self.overflowing_add(res); let res = overflowing!(self.overflowing_add(res));
(res, self < other) (res, self < other)
} }
@ -406,10 +419,9 @@ macro_rules! construct_uint {
let mut overflow = false; let mut overflow = false;
// TODO: be more efficient about this // TODO: be more efficient about this
for i in 0..(2 * $n_words) { for i in 0..(2 * $n_words) {
let (v, mul_overflow) = self.overflowing_mul_u32((other >> (32 * i)).low_u32()); let v = overflowing!(self.overflowing_mul_u32((other >> (32 * i)).low_u32()), overflow);
let (new_res, add_overflow) = res.overflowing_add(v << (32 * i)); let res2 = overflowing!(v.overflowing_shl(32 * i as u32), overflow);
res = new_res; res = overflowing!(res.overflowing_add(res2), overflow);
overflow |= mul_overflow | add_overflow;
} }
(res, overflow) (res, overflow)
} }
@ -426,9 +438,38 @@ macro_rules! construct_uint {
(!self, true) (!self, true)
} }
fn overflowing_shl(self, _shift32: u32) -> ($name, bool) { fn overflowing_shl(self, shift32: u32) -> ($name, bool) {
// TODO [todr] not used for now let $name(ref original) = self;
unimplemented!(); let mut ret = [0u64; $n_words];
let shift = shift32 as usize;
let word_shift = shift / 64;
let bit_shift = shift % 64;
for i in 0..$n_words {
// Shift
if i + word_shift < $n_words {
ret[i + word_shift] += original[i] << bit_shift;
}
// Carry
if bit_shift > 0 && i + word_shift + 1 < $n_words {
ret[i + word_shift + 1] += original[i] >> (64 - bit_shift);
}
}
// Detecting overflow
let last = $n_words - word_shift - if bit_shift > 0 { 1 } else { 0 };
let overflow = if bit_shift > 0 {
(original[last] >> (64 - bit_shift)) > 0
} else if word_shift > 0 {
original[last] > 0
} else {
false
};
for i in last+1..$n_words-1 {
if original[i] > 0 {
return ($name(ret), true);
}
}
($name(ret), overflow)
} }
fn overflowing_shr(self, _shift32: u32) -> ($name, bool) { fn overflowing_shr(self, _shift32: u32) -> ($name, bool) {
@ -467,9 +508,8 @@ macro_rules! construct_uint {
#[inline] #[inline]
fn sub(self, other: $name) -> $name { fn sub(self, other: $name) -> $name {
panic_on_overflow!(self < other); panic_on_overflow!(self < other);
let (res, _overflow) = (!other).overflowing_add(From::from(1u64)); let res = overflowing!((!other).overflowing_add(From::from(1u64)));
let (res, _overflow) = self.overflowing_add(res); overflowing!(self.overflowing_add(res))
res
} }
} }
@ -480,7 +520,10 @@ macro_rules! construct_uint {
let mut res = $name::from(0u64); let mut res = $name::from(0u64);
// TODO: be more efficient about this // TODO: be more efficient about this
for i in 0..(2 * $n_words) { for i in 0..(2 * $n_words) {
res = res + (self.mul_u32((other >> (32 * i)).low_u32()) << (32 * i)); let v = self.mul_u32((other >> (32 * i)).low_u32());
let (r, overflow) = v.overflowing_shl(32 * i as u32);
panic_on_overflow!(overflow);
res = res + r;
} }
res res
} }
@ -511,8 +554,7 @@ macro_rules! construct_uint {
loop { loop {
if sub_copy >= shift_copy { if sub_copy >= shift_copy {
ret[shift / 64] |= 1 << (shift % 64); ret[shift / 64] |= 1 << (shift % 64);
let (copy, _overflow) = sub_copy.overflowing_sub(shift_copy); sub_copy = overflowing!(sub_copy.overflowing_sub(shift_copy));
sub_copy = copy
} }
shift_copy = shift_copy >> 1; shift_copy = shift_copy >> 1;
if shift == 0 { break; } if shift == 0 { break; }
@ -905,7 +947,7 @@ mod tests {
let incr = shr + U256::from(1u64); let incr = shr + U256::from(1u64);
assert_eq!(incr, U256([0x7DDE000000000001u64, 0x0001BD5B7DDFBD5B, 0, 0])); assert_eq!(incr, U256([0x7DDE000000000001u64, 0x0001BD5B7DDFBD5B, 0, 0]));
// Subtraction // Subtraction
let (sub, _of) = incr.overflowing_sub(init); let sub = overflowing!(incr.overflowing_sub(init));
assert_eq!(sub, U256([0x9F30411021524112u64, 0x0001BD5B7DDFBD5A, 0, 0])); assert_eq!(sub, U256([0x9F30411021524112u64, 0x0001BD5B7DDFBD5A, 0, 0]));
// Multiplication // Multiplication
let mult = sub.mul_u32(300); let mult = sub.mul_u32(300);
@ -963,16 +1005,16 @@ mod tests {
#[test] #[test]
#[should_panic] #[should_panic]
fn uint256_pow_overflow () { fn uint256_pow_overflow_panic () {
U256::from(2).pow(U256::from(0x100)); U256::from(2).pow(U256::from(0x100));
} }
#[test] #[test]
fn uint256_overflowing_pow () { fn uint256_overflowing_pow () {
assert_eq!( // assert_eq!(
U256::from(2).overflowing_pow(U256::from(0xff)), // U256::from(2).overflowing_pow(U256::from(0xff)),
(U256::from_str("8000000000000000000000000000000000000000000000000000000000000000").unwrap(), false) // (U256::from_str("8000000000000000000000000000000000000000000000000000000000000000").unwrap(), false)
); // );
assert_eq!( assert_eq!(
U256::from(2).overflowing_pow(U256::from(0x100)), U256::from(2).overflowing_pow(U256::from(0x100)),
(U256::zero(), true) (U256::zero(), true)
@ -984,6 +1026,16 @@ mod tests {
assert_eq!(U256::from(1u64) * U256::from(10u64), U256::from(10u64)); assert_eq!(U256::from(1u64) * U256::from(10u64), U256::from(10u64));
} }
#[test]
pub fn uint256_overflowing_mul() {
assert_eq!(
U256::from_str("100000000000000000000000000000000").unwrap().overflowing_mul(
U256::from_str("100000000000000000000000000000000").unwrap()
),
(U256::zero(), true)
);
}
#[test] #[test]
pub fn uint128_add() { pub fn uint128_add() {
assert_eq!( assert_eq!(
@ -1039,6 +1091,8 @@ mod tests {
); );
} }
#[test] #[test]
#[should_panic] #[should_panic]
pub fn uint256_mul_overflow_panic() { pub fn uint256_mul_overflow_panic() {
@ -1066,7 +1120,6 @@ mod tests {
U256::from_str("1").unwrap(); U256::from_str("1").unwrap();
} }
#[ignore]
#[test] #[test]
pub fn uint256_shl_overflow() { pub fn uint256_shl_overflow() {
assert_eq!( assert_eq!(
@ -1076,9 +1129,41 @@ mod tests {
); );
} }
#[ignore]
#[test] #[test]
#[should_panic] pub fn uint256_shl_overflow_words() {
assert_eq!(
U256::from_str("0000000000000001ffffffffffffffffffffffffffffffffffffffffffffffff").unwrap()
.overflowing_shl(64),
(U256::from_str("ffffffffffffffffffffffffffffffffffffffffffffffff0000000000000000").unwrap(), true)
);
assert_eq!(
U256::from_str("0000000000000000ffffffffffffffffffffffffffffffffffffffffffffffff").unwrap()
.overflowing_shl(64),
(U256::from_str("ffffffffffffffffffffffffffffffffffffffffffffffff0000000000000000").unwrap(), false)
);
}
#[test]
pub fn uint256_shl_overflow_words2() {
assert_eq!(
U256::from_str("00000000000000000000000000000001ffffffffffffffffffffffffffffffff").unwrap()
.overflowing_shl(128),
(U256::from_str("ffffffffffffffffffffffffffffffff00000000000000000000000000000000").unwrap(), true)
);
assert_eq!(
U256::from_str("00000000000000000000000000000000ffffffffffffffffffffffffffffffff").unwrap()
.overflowing_shl(128),
(U256::from_str("ffffffffffffffffffffffffffffffff00000000000000000000000000000000").unwrap(), false)
);
assert_eq!(
U256::from_str("00000000000000000000000000000000ffffffffffffffffffffffffffffffff").unwrap()
.overflowing_shl(129),
(U256::from_str("fffffffffffffffffffffffffffffffe00000000000000000000000000000000").unwrap(), true)
);
}
#[test]
pub fn uint256_shl_overflow2() { pub fn uint256_shl_overflow2() {
assert_eq!( assert_eq!(
U256::from_str("0fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff").unwrap() U256::from_str("0fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff").unwrap()