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Saturating math #8323

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5f713da
Add std::num::Saturating
lilyball Aug 6, 2013
3db3ce2
Update Iterator impls to use Saturating
lilyball Aug 6, 2013
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35 changes: 10 additions & 25 deletions src/libstd/iterator.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -18,7 +18,7 @@ implementing the `Iterator` trait.
*/

use cmp;
use num::{Zero, One};
use num::{Zero, One, Saturating};
use option::{Option, Some, None};
use ops::{Add, Mul};
use cmp::Ord;
Expand Down Expand Up @@ -863,15 +863,10 @@ impl<A, T: Iterator<A>, U: Iterator<A>> Iterator<A> for Chain<T, U> {
let (a_lower, a_upper) = self.a.size_hint();
let (b_lower, b_upper) = self.b.size_hint();

let lower = if uint::max_value - a_lower < b_lower {
uint::max_value
} else {
a_lower + b_lower
};
let lower = a_lower.saturating_add(b_lower);

let upper = match (a_upper, b_upper) {
(Some(x), Some(y)) if uint::max_value - x < y => Some(uint::max_value),
(Some(x), Some(y)) => Some(x + y),
(Some(x), Some(y)) => Some(x.saturating_add(y)),
_ => None
};

Expand All @@ -895,12 +890,7 @@ for Chain<T, U> {
#[inline]
fn indexable(&self) -> uint {
let (a, b) = (self.a.indexable(), self.b.indexable());
let total = a + b;
if total < a || total < b {
uint::max_value
} else {
total
}
a.saturating_add(b)
}

#[inline]
Expand Down Expand Up @@ -1252,11 +1242,10 @@ impl<A, T: Iterator<A>> Iterator<A> for Skip<T> {
fn size_hint(&self) -> (uint, Option<uint>) {
let (lower, upper) = self.iter.size_hint();

let lower = if lower >= self.n { lower - self.n } else { 0 };
let lower = lower.saturating_sub(self.n);

let upper = match upper {
Some(x) if x >= self.n => Some(x - self.n),
Some(_) => Some(0),
Some(x) => Some(x.saturating_sub(self.n)),
None => None
};

Expand All @@ -1267,12 +1256,7 @@ impl<A, T: Iterator<A>> Iterator<A> for Skip<T> {
impl<A, T: RandomAccessIterator<A>> RandomAccessIterator<A> for Skip<T> {
#[inline]
fn indexable(&self) -> uint {
let N = self.iter.indexable();
if N < self.n {
0
} else {
N - self.n
}
self.iter.indexable().saturating_sub(self.n)
}

#[inline]
Expand Down Expand Up @@ -1389,9 +1373,10 @@ impl<'self, A, T: Iterator<A>, B, U: Iterator<B>> Iterator<B> for
fn size_hint(&self) -> (uint, Option<uint>) {
let (flo, fhi) = self.frontiter.map_default((0, Some(0)), |it| it.size_hint());
let (blo, bhi) = self.backiter.map_default((0, Some(0)), |it| it.size_hint());
let lo = flo.saturating_add(blo);
match (self.iter.size_hint(), fhi, bhi) {
((0, Some(0)), Some(a), Some(b)) => (flo + blo, Some(a + b)),
_ => (flo + blo, None)
((0, Some(0)), Some(a), Some(b)) => (lo, Some(a.saturating_add(b))),
_ => (lo, None)
}
}
}
Expand Down
217 changes: 157 additions & 60 deletions src/libstd/num/num.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -466,6 +466,56 @@ impl<T: Zero> Zero for ~T {
fn is_zero(&self) -> bool { (**self).is_zero() }
}

/// Saturating math operations
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It seems odd to use static methods here - is there a reason not to use normal methods?

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I didn't like the idea of saying a.saturating_add(b). Just seemed odd to me.

pub trait Saturating: Int {
/// Saturating addition operator.
/// Returns a+b, saturating at the numeric bounds instead of overflowing.
#[inline]
fn saturating_add(self, v: Self) -> Self {
let x = self + v;
if v >= Zero::zero() {
if x < self {
// overflow
Bounded::max_value::<Self>()
} else { x }
} else {
if x > self {
// underflow
Bounded::min_value::<Self>()
} else { x }
}
}

/// Saturating subtraction operator.
/// Returns a-b, saturating at the numeric bounds instead of overflowing.
#[inline]
fn saturating_sub(self, v: Self) -> Self {
let x = self - v;
if v >= Zero::zero() {
if x > self {
// underflow
Bounded::min_value::<Self>()
} else { x }
} else {
if x < self {
// overflow
Bounded::max_value::<Self>()
} else { x }
}
}
}

impl Saturating for int {}
impl Saturating for i8 {}
impl Saturating for i16 {}
impl Saturating for i32 {}
impl Saturating for i64 {}
impl Saturating for uint {}
impl Saturating for u8 {}
impl Saturating for u16 {}
impl Saturating for u32 {}
impl Saturating for u64 {}

/// Helper function for testing numeric operations
#[cfg(test)]
pub fn test_num<T:Num + NumCast>(ten: T, two: T) {
Expand All @@ -482,64 +532,111 @@ pub fn test_num<T:Num + NumCast>(ten: T, two: T) {
assert_eq!(ten.rem(&two), ten % two);
}

macro_rules! test_cast_20(
($_20:expr) => ({
let _20 = $_20;

assert_eq!(20u, _20.to_uint());
assert_eq!(20u8, _20.to_u8());
assert_eq!(20u16, _20.to_u16());
assert_eq!(20u32, _20.to_u32());
assert_eq!(20u64, _20.to_u64());
assert_eq!(20i, _20.to_int());
assert_eq!(20i8, _20.to_i8());
assert_eq!(20i16, _20.to_i16());
assert_eq!(20i32, _20.to_i32());
assert_eq!(20i64, _20.to_i64());
assert_eq!(20f, _20.to_float());
assert_eq!(20f32, _20.to_f32());
assert_eq!(20f64, _20.to_f64());

assert_eq!(_20, NumCast::from(20u));
assert_eq!(_20, NumCast::from(20u8));
assert_eq!(_20, NumCast::from(20u16));
assert_eq!(_20, NumCast::from(20u32));
assert_eq!(_20, NumCast::from(20u64));
assert_eq!(_20, NumCast::from(20i));
assert_eq!(_20, NumCast::from(20i8));
assert_eq!(_20, NumCast::from(20i16));
assert_eq!(_20, NumCast::from(20i32));
assert_eq!(_20, NumCast::from(20i64));
assert_eq!(_20, NumCast::from(20f));
assert_eq!(_20, NumCast::from(20f32));
assert_eq!(_20, NumCast::from(20f64));

assert_eq!(_20, cast(20u));
assert_eq!(_20, cast(20u8));
assert_eq!(_20, cast(20u16));
assert_eq!(_20, cast(20u32));
assert_eq!(_20, cast(20u64));
assert_eq!(_20, cast(20i));
assert_eq!(_20, cast(20i8));
assert_eq!(_20, cast(20i16));
assert_eq!(_20, cast(20i32));
assert_eq!(_20, cast(20i64));
assert_eq!(_20, cast(20f));
assert_eq!(_20, cast(20f32));
assert_eq!(_20, cast(20f64));
})
)
#[cfg(test)]
mod tests {
use super::*;

macro_rules! test_cast_20(
($_20:expr) => ({
let _20 = $_20;

assert_eq!(20u, _20.to_uint());
assert_eq!(20u8, _20.to_u8());
assert_eq!(20u16, _20.to_u16());
assert_eq!(20u32, _20.to_u32());
assert_eq!(20u64, _20.to_u64());
assert_eq!(20i, _20.to_int());
assert_eq!(20i8, _20.to_i8());
assert_eq!(20i16, _20.to_i16());
assert_eq!(20i32, _20.to_i32());
assert_eq!(20i64, _20.to_i64());
assert_eq!(20f, _20.to_float());
assert_eq!(20f32, _20.to_f32());
assert_eq!(20f64, _20.to_f64());

assert_eq!(_20, NumCast::from(20u));
assert_eq!(_20, NumCast::from(20u8));
assert_eq!(_20, NumCast::from(20u16));
assert_eq!(_20, NumCast::from(20u32));
assert_eq!(_20, NumCast::from(20u64));
assert_eq!(_20, NumCast::from(20i));
assert_eq!(_20, NumCast::from(20i8));
assert_eq!(_20, NumCast::from(20i16));
assert_eq!(_20, NumCast::from(20i32));
assert_eq!(_20, NumCast::from(20i64));
assert_eq!(_20, NumCast::from(20f));
assert_eq!(_20, NumCast::from(20f32));
assert_eq!(_20, NumCast::from(20f64));

assert_eq!(_20, cast(20u));
assert_eq!(_20, cast(20u8));
assert_eq!(_20, cast(20u16));
assert_eq!(_20, cast(20u32));
assert_eq!(_20, cast(20u64));
assert_eq!(_20, cast(20i));
assert_eq!(_20, cast(20i8));
assert_eq!(_20, cast(20i16));
assert_eq!(_20, cast(20i32));
assert_eq!(_20, cast(20i64));
assert_eq!(_20, cast(20f));
assert_eq!(_20, cast(20f32));
assert_eq!(_20, cast(20f64));
})
)

#[test] fn test_u8_cast() { test_cast_20!(20u8) }
#[test] fn test_u16_cast() { test_cast_20!(20u16) }
#[test] fn test_u32_cast() { test_cast_20!(20u32) }
#[test] fn test_u64_cast() { test_cast_20!(20u64) }
#[test] fn test_uint_cast() { test_cast_20!(20u) }
#[test] fn test_i8_cast() { test_cast_20!(20i8) }
#[test] fn test_i16_cast() { test_cast_20!(20i16) }
#[test] fn test_i32_cast() { test_cast_20!(20i32) }
#[test] fn test_i64_cast() { test_cast_20!(20i64) }
#[test] fn test_int_cast() { test_cast_20!(20i) }
#[test] fn test_f32_cast() { test_cast_20!(20f32) }
#[test] fn test_f64_cast() { test_cast_20!(20f64) }
#[test] fn test_float_cast() { test_cast_20!(20f) }

#[test]
fn test_saturating_add_uint() {
use uint::max_value;
assert_eq!(3u.saturating_add(5u), 8u);
assert_eq!(3u.saturating_add(max_value-1), max_value);
assert_eq!(max_value.saturating_add(max_value), max_value);
assert_eq!((max_value-2).saturating_add(1), max_value-1);
}

#[test]
fn test_saturating_sub_uint() {
use uint::max_value;
assert_eq!(5u.saturating_sub(3u), 2u);
assert_eq!(3u.saturating_sub(5u), 0u);
assert_eq!(0u.saturating_sub(1u), 0u);
assert_eq!((max_value-1).saturating_sub(max_value), 0);
}

#[test] fn test_u8_cast() { test_cast_20!(20u8) }
#[test] fn test_u16_cast() { test_cast_20!(20u16) }
#[test] fn test_u32_cast() { test_cast_20!(20u32) }
#[test] fn test_u64_cast() { test_cast_20!(20u64) }
#[test] fn test_uint_cast() { test_cast_20!(20u) }
#[test] fn test_i8_cast() { test_cast_20!(20i8) }
#[test] fn test_i16_cast() { test_cast_20!(20i16) }
#[test] fn test_i32_cast() { test_cast_20!(20i32) }
#[test] fn test_i64_cast() { test_cast_20!(20i64) }
#[test] fn test_int_cast() { test_cast_20!(20i) }
#[test] fn test_f32_cast() { test_cast_20!(20f32) }
#[test] fn test_f64_cast() { test_cast_20!(20f64) }
#[test] fn test_float_cast() { test_cast_20!(20f) }
#[test]
fn test_saturating_add_int() {
use int::{min_value,max_value};
assert_eq!(3i.saturating_add(5i), 8i);
assert_eq!(3i.saturating_add(max_value-1), max_value);
assert_eq!(max_value.saturating_add(max_value), max_value);
assert_eq!((max_value-2).saturating_add(1), max_value-1);
assert_eq!(3i.saturating_add(-5i), -2i);
assert_eq!(min_value.saturating_add(-1i), min_value);
assert_eq!((-2i).saturating_add(-max_value), min_value);
}

#[test]
fn test_saturating_sub_int() {
use int::{min_value,max_value};
assert_eq!(3i.saturating_sub(5i), -2i);
assert_eq!(min_value.saturating_sub(1i), min_value);
assert_eq!((-2i).saturating_sub(max_value), min_value);
assert_eq!(3i.saturating_sub(-5i), 8i);
assert_eq!(3i.saturating_sub(-(max_value-1)), max_value);
assert_eq!(max_value.saturating_sub(-max_value), max_value);
assert_eq!((max_value-2).saturating_sub(-1), max_value-1);
}
}