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improve the TryFrom implementations
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This removes the need for a 128 bit storage by making use of the fact that
there can be either no over/underflow, either one or both, and each time
the target type suffices to hold the limit for comparison.

The downside is that the code looks a bit more complex.

This test code included in this commit is from @oyvindln 's PR. They also
greatly helped fixing a number of errors I made along the way. Thanks a lot!
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@llogiq
llogiq committed Jul 24, 2017
1 parent b4502f7 commit 72ef15e
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Showing 2 changed files with 391 additions and 38 deletions.
215 changes: 177 additions & 38 deletions src/libcore/num/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2504,76 +2504,209 @@ impl fmt::Display for TryFromIntError {
}
}

macro_rules! same_sign_try_from_int_impl {
($storage:ty, $target:ty, $($source:ty),*) => {$(
// no possible bounds violation
macro_rules! try_from_unbounded {
($source:ty, $($target:ty),*) => {$(
#[unstable(feature = "try_from", issue = "33417")]
impl TryFrom<$source> for $target {
type Error = TryFromIntError;

#[inline]
fn try_from(u: $source) -> Result<$target, TryFromIntError> {
let min = <$target as FromStrRadixHelper>::min_value() as $storage;
let max = <$target as FromStrRadixHelper>::max_value() as $storage;
if u as $storage < min || u as $storage > max {
Err(TryFromIntError(()))
} else {
Ok(u as $target)
}
}
)*}
}

// only negative bounds
macro_rules! try_from_lower_bounded {
($source:ty, $($target:ty),*) => {$(
#[unstable(feature = "try_from", issue = "33417")]
impl TryFrom<$source> for $target {
type Error = TryFromIntError;

#[inline]
fn try_from(u: $source) -> Result<$target, TryFromIntError> {
if u >= 0 {
Ok(u as $target)
} else {
Err(TryFromIntError(()))
}
}
}
)*}
}

same_sign_try_from_int_impl!(u128, u8, u8, u16, u32, u64, u128, usize);
same_sign_try_from_int_impl!(i128, i8, i8, i16, i32, i64, i128, isize);
same_sign_try_from_int_impl!(u128, u16, u8, u16, u32, u64, u128, usize);
same_sign_try_from_int_impl!(i128, i16, i8, i16, i32, i64, i128, isize);
same_sign_try_from_int_impl!(u128, u32, u8, u16, u32, u64, u128, usize);
same_sign_try_from_int_impl!(i128, i32, i8, i16, i32, i64, i128, isize);
same_sign_try_from_int_impl!(u128, u64, u8, u16, u32, u64, u128, usize);
same_sign_try_from_int_impl!(i128, i64, i8, i16, i32, i64, i128, isize);
same_sign_try_from_int_impl!(u128, u128, u8, u16, u32, u64, u128, usize);
same_sign_try_from_int_impl!(i128, i128, i8, i16, i32, i64, i128, isize);
same_sign_try_from_int_impl!(u128, usize, u8, u16, u32, u64, u128, usize);
same_sign_try_from_int_impl!(i128, isize, i8, i16, i32, i64, i128, isize);

macro_rules! cross_sign_from_int_impl {
($unsigned:ty, $($signed:ty),*) => {$(
// unsigned to signed (only positive bound)
macro_rules! try_from_upper_bounded {
($source:ty, $($target:ty),*) => {$(
#[unstable(feature = "try_from", issue = "33417")]
impl TryFrom<$unsigned> for $signed {
impl TryFrom<$source> for $target {
type Error = TryFromIntError;

fn try_from(u: $unsigned) -> Result<$signed, TryFromIntError> {
let max = <$signed as FromStrRadixHelper>::max_value() as u128;
if u as u128 > max {
#[inline]
fn try_from(u: $source) -> Result<$target, TryFromIntError> {
if u > (<$target>::max_value() as $source) {
Err(TryFromIntError(()))
} else {
Ok(u as $signed)
Ok(u as $target)
}
}
}
)*}
}

// all other cases
macro_rules! try_from_both_bounded {
($source:ty, $($target:ty),*) => {$(
#[unstable(feature = "try_from", issue = "33417")]
impl TryFrom<$signed> for $unsigned {
impl TryFrom<$source> for $target {
type Error = TryFromIntError;

fn try_from(u: $signed) -> Result<$unsigned, TryFromIntError> {
let max = <$unsigned as FromStrRadixHelper>::max_value() as u128;
if u < 0 || u as u128 > max {
#[inline]
fn try_from(u: $source) -> Result<$target, TryFromIntError> {
let min = <$target>::min_value() as $source;
let max = <$target>::max_value() as $source;
if u < min || u > max {
Err(TryFromIntError(()))
} else {
Ok(u as $unsigned)
Ok(u as $target)
}
}
}
)*}
}

cross_sign_from_int_impl!(u8, i8, i16, i32, i64, i128, isize);
cross_sign_from_int_impl!(u16, i8, i16, i32, i64, i128, isize);
cross_sign_from_int_impl!(u32, i8, i16, i32, i64, i128, isize);
cross_sign_from_int_impl!(u64, i8, i16, i32, i64, i128, isize);
cross_sign_from_int_impl!(u128, i8, i16, i32, i64, i128, isize);
cross_sign_from_int_impl!(usize, i8, i16, i32, i64, i128, isize);
macro_rules! rev {
($mac:ident, $source:ty, $($target:ty),*) => {$(
$mac!($target, $source);
)*}
}

/// intra-sign conversions
try_from_unbounded!(u8, u8, u16, u32, u64, u128);
try_from_unbounded!(u16, u16, u32, u64, u128);
try_from_unbounded!(u32, u32, u64, u128);
try_from_unbounded!(u64, u64, u128);
try_from_unbounded!(u128, u128);
try_from_upper_bounded!(u16, u8);
try_from_upper_bounded!(u32, u16, u8);
try_from_upper_bounded!(u64, u32, u16, u8);
try_from_upper_bounded!(u128, u64, u32, u16, u8);

try_from_unbounded!(i8, i8, i16, i32, i64, i128);
try_from_unbounded!(i16, i16, i32, i64, i128);
try_from_unbounded!(i32, i32, i64, i128);
try_from_unbounded!(i64, i64, i128);
try_from_unbounded!(i128, i128);
try_from_both_bounded!(i16, i8);
try_from_both_bounded!(i32, i16, i8);
try_from_both_bounded!(i64, i32, i16, i8);
try_from_both_bounded!(i128, i64, i32, i16, i8);

// unsigned-to-signed
try_from_unbounded!(u8, i16, i32, i64, i128);
try_from_unbounded!(u16, i32, i64, i128);
try_from_unbounded!(u32, i64, i128);
try_from_unbounded!(u64, i128);
try_from_upper_bounded!(u8, i8);
try_from_upper_bounded!(u16, i8, i16);
try_from_upper_bounded!(u32, i8, i16, i32);
try_from_upper_bounded!(u64, i8, i16, i32, i64);
try_from_upper_bounded!(u128, i8, i16, i32, i64, i128);

// signed-to-unsigned
try_from_lower_bounded!(i8, u8, u16, u32, u64, u128);
try_from_lower_bounded!(i16, u16, u32, u64, u128);
try_from_lower_bounded!(i32, u32, u64, u128);
try_from_lower_bounded!(i64, u64, u128);
try_from_lower_bounded!(i128, u128);
try_from_both_bounded!(i16, u8);
try_from_both_bounded!(i32, u16, u8);
try_from_both_bounded!(i64, u32, u16, u8);
try_from_both_bounded!(i128, u64, u32, u16, u8);

#[unstable(feature = "try_from", issue = "33417")]
pub use self::ptr_try_from_impls::*;

#[cfg(target_pointer_width = "16")]
mod ptr_try_from_impls {
use super::TryFromIntError;
use convert::TryFrom;

try_from_upper_bounded!(usize, u8);
try_from_unbounded!(usize, usize, u16, u32, u64, u128);
try_from_upper_bounded!(usize, i8, i16, isize);
try_from_unbounded!(usize, i32, i64, i128);

try_from_both_bounded!(isize, u8);
try_from_lower_bounded!(isize, usize, u16, u32, u64, u128);
try_from_both_bounded!(isize, i8);
try_from_unbounded!(isize, i16, i32, i64, i128);

rev!(try_from_unbounded, usize, u8, u16);
rev!(try_from_upper_bounded, usize, u32, u64, u128);
rev!(try_from_lower_bounded, usize, i8, i16);
rev!(try_from_both_bounded, usize, i32, i64, i128);

rev!(try_from_unbounded, isize, u8);
rev!(try_from_upper_bounded, isize, u16, u32, u64, u128);
rev!(try_from_unbounded, isize, i8, i16);
rev!(try_from_both_bounded, isize, i32, i64, i128);
}

#[cfg(target_pointer_width = "32")]
mod ptr_try_from_impls {
use super::TryFromIntError;
use convert::TryFrom;

try_from_upper_bounded!(usize, u8, u16);
try_from_unbounded!(usize, usize, u32, u64, u128);
try_from_upper_bounded!(usize, i8, i16, i32, isize);
try_from_unbounded!(usize, i64, i128);

try_from_both_bounded!(isize, u8, u16);
try_from_lower_bounded!(isize, usize, u32, u64, u128);
try_from_both_bounded!(isize, i8, i16);
try_from_unbounded!(isize, i32, i64, i128);

rev!(try_from_unbounded, usize, u8, u16, u32);
rev!(try_from_upper_bounded, usize, u64, u128);
rev!(try_from_lower_bounded, usize, i8, i16, i32);
rev!(try_from_both_bounded, usize, i64, i128);

rev!(try_from_unbounded, isize, u8, u16);
rev!(try_from_upper_bounded, isize, u32, u64, u128);
rev!(try_from_unbounded, isize, i8, i16, i32);
rev!(try_from_both_bounded, isize, i64, i128);
}

#[cfg(target_pointer_width = "64")]
mod ptr_try_from_impls {
use super::TryFromIntError;
use convert::TryFrom;

try_from_upper_bounded!(usize, u8, u16, u32);
try_from_unbounded!(usize, usize, u64, u128);
try_from_upper_bounded!(usize, i8, i16, i32, i64, isize);
try_from_unbounded!(usize, i128);

try_from_both_bounded!(isize, u8, u16, u32);
try_from_lower_bounded!(isize, usize, u64, u128);
try_from_both_bounded!(isize, i8, i16, i32);
try_from_unbounded!(isize, i64, i128);

rev!(try_from_unbounded, usize, u8, u16, u32, u64);
rev!(try_from_upper_bounded, usize, u128);
rev!(try_from_lower_bounded, usize, i8, i16, i32, i64);
rev!(try_from_both_bounded, usize, i128);

rev!(try_from_unbounded, isize, u8, u16, u32);
rev!(try_from_upper_bounded, isize, u64, u128);
rev!(try_from_unbounded, isize, i8, i16, i32, i64);
rev!(try_from_both_bounded, isize, i128);
}

#[doc(hidden)]
trait FromStrRadixHelper: PartialOrd + Copy {
Expand All @@ -2587,15 +2720,21 @@ trait FromStrRadixHelper: PartialOrd + Copy {

macro_rules! doit {
($($t:ty)*) => ($(impl FromStrRadixHelper for $t {
#[inline]
fn min_value() -> Self { Self::min_value() }
#[inline]
fn max_value() -> Self { Self::max_value() }
#[inline]
fn from_u32(u: u32) -> Self { u as Self }
#[inline]
fn checked_mul(&self, other: u32) -> Option<Self> {
Self::checked_mul(*self, other as Self)
}
#[inline]
fn checked_sub(&self, other: u32) -> Option<Self> {
Self::checked_sub(*self, other as Self)
}
#[inline]
fn checked_add(&self, other: u32) -> Option<Self> {
Self::checked_add(*self, other as Self)
}
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