cadd 0.1.1

Painless checked arithmetics and conversions
Documentation 
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use core::num::NonZero;

macro_rules! impl_nonzero_int_cfrom_nonzero_int {
    ($source:ty => $($target:ty),+) => {
        super::impl_cfrom!(
            $((NonZero<$source>, NonZero<$target>),)*
        );
    };
}

// unsigned non-zero integer -> unsigned non-zero integer
impl_nonzero_int_cfrom_nonzero_int!(u16 => u8);
impl_nonzero_int_cfrom_nonzero_int!(u32 => u8, u16, usize);
impl_nonzero_int_cfrom_nonzero_int!(u64 => u8, u16, u32, usize);
impl_nonzero_int_cfrom_nonzero_int!(u128 => u8, u16, u32, u64, usize);
impl_nonzero_int_cfrom_nonzero_int!(usize => u8, u16, u32, u64, u128);

// signed non-zero integer -> signed non-zero integer
impl_nonzero_int_cfrom_nonzero_int!(i16 => i8);
impl_nonzero_int_cfrom_nonzero_int!(i32 => i8, i16, isize);
impl_nonzero_int_cfrom_nonzero_int!(i64 => i8, i16, i32, isize);
impl_nonzero_int_cfrom_nonzero_int!(i128 => i8, i16, i32, i64, isize);
impl_nonzero_int_cfrom_nonzero_int!(isize => i8, i16, i32, i64, i128);

// unsigned non-zero integer -> signed non-zero integer
impl_nonzero_int_cfrom_nonzero_int!(u8 => i8);
impl_nonzero_int_cfrom_nonzero_int!(u16 => i8, i16, isize);
impl_nonzero_int_cfrom_nonzero_int!(u32 => i8, i16, i32, isize);
impl_nonzero_int_cfrom_nonzero_int!(u64 => i8, i16, i32, i64, isize);
impl_nonzero_int_cfrom_nonzero_int!(u128 => i8, i16, i32, i64, i128, isize);
impl_nonzero_int_cfrom_nonzero_int!(usize => i8, i16, i32, i64, i128, isize);

// signed non-zero integer -> unsigned non-zero integer
impl_nonzero_int_cfrom_nonzero_int!(i8 => u8, u16, u32, u64, u128, usize);
impl_nonzero_int_cfrom_nonzero_int!(i16 => u8, u16, u32, u64, u128, usize);
impl_nonzero_int_cfrom_nonzero_int!(i32 => u8, u16, u32, u64, u128, usize);
impl_nonzero_int_cfrom_nonzero_int!(i64 => u8, u16, u32, u64, u128, usize);
impl_nonzero_int_cfrom_nonzero_int!(i128 => u8, u16, u32, u64, u128, usize);
impl_nonzero_int_cfrom_nonzero_int!(isize => u8, u16, u32, u64, u128, usize);

// The macros and invokations below are modelled after `std::convert::num`.

// no possible bounds violation
macro_rules! impl_cfrom_unbounded {
    ($source:ty => $($target:ty),+) => {$(
        impl $crate::convert::Cfrom<$source> for $target {
            type Error = $crate::Error;
            #[inline]
            fn cfrom(u: $source) -> $crate::Result<Self> {
                Ok(u as Self)
            }
        }

        impl $crate::convert::SaturatingFrom<$source> for $target {
            #[inline]
            fn saturating_from(u: $source) -> Self {
                u as Self
            }
        }
    )*}
}

// only negative bounds
macro_rules! impl_cfrom_lower_bounded {
    ($source:ty => $($target:ty),+) => {$(
        impl $crate::convert::Cfrom<$source> for $target {
            type Error = $crate::Error;
            #[inline]
            fn cfrom(u: $source) -> $crate::Result<Self> {
                if u >= 0 {
                    Ok(u as Self)
                } else {
                    Err($crate::Error::new(
                        ::alloc::format!(
                            "cannot convert value {:?} from {} to {}: value is out of bounds",
                            u,
                            ::core::any::type_name::<$source>(),
                            ::core::any::type_name::<$target>(),
                        )
                    ))
                }
            }
        }

        impl $crate::convert::SaturatingFrom<$source> for $target {
            #[inline]
            fn saturating_from(u: $source) -> Self {
                if u >= 0 {
                    u as Self
                } else {
                    0
                }
            }
        }
    )*}
}

// unsigned to signed (only positive bound)
macro_rules! impl_cfrom_upper_bounded {
    ($source:ty => $($target:ty),+) => {$(
        impl $crate::convert::Cfrom<$source> for $target {
            type Error = $crate::Error;
            #[inline]
            fn cfrom(u: $source) -> $crate::Result<Self> {
                if u > (Self::MAX as $source) {
                    Err($crate::Error::new(
                        ::alloc::format!(
                            "cannot convert value {:?} from {} to {}: value is out of bounds",
                            u,
                            ::core::any::type_name::<$source>(),
                            ::core::any::type_name::<$target>(),
                        )
                    ))
                } else {
                    Ok(u as Self)
                }
            }
        }

        impl $crate::convert::SaturatingFrom<$source> for $target {
            #[inline]
            fn saturating_from(u: $source) -> Self {
                if u > (Self::MAX as $source) {
                    Self::MAX
                } else {
                    u as Self
                }
            }
        }
    )*}
}

// all other cases
macro_rules! impl_cfrom_both_bounded {
    ($source:ty => $($target:ty),+) => {$(
        impl $crate::convert::Cfrom<$source> for $target {
            type Error = $crate::Error;
            #[inline]
            fn cfrom(u: $source) -> $crate::Result<Self> {
                let min = Self::MIN as $source;
                let max = Self::MAX as $source;
                if u < min || u > max {
                    Err($crate::Error::new(
                        ::alloc::format!(
                            "cannot convert value {:?} from {} to {}: value is out of bounds",
                            u,
                            ::core::any::type_name::<$source>(),
                            ::core::any::type_name::<$target>(),
                        )
                    ))
                } else {
                    Ok(u as Self)
                }
            }
        }

        impl $crate::convert::SaturatingFrom<$source> for $target {
            #[inline]
            fn saturating_from(u: $source) -> Self {
                let min = Self::MIN as $source;
                let max = Self::MAX as $source;
                if u < min {
                    Self::MIN
                } else if u > max {
                    Self::MAX
                } else {
                    u as Self
                }
            }
        }
    )*}
}

macro_rules! rev {
    ($mac:ident, $source:ty => $($target:ty),+) => {$(
        $mac!($target => $source);
    )*}
}

// unsigned integer -> unsigned integer
impl_cfrom_upper_bounded!(u16 => u8);
impl_cfrom_upper_bounded!(u32 => u8, u16);
impl_cfrom_upper_bounded!(u64 => u8, u16, u32);
impl_cfrom_upper_bounded!(u128 => u8, u16, u32, u64);

// signed integer -> signed integer
impl_cfrom_both_bounded!(i16 => i8);
impl_cfrom_both_bounded!(i32 => i8, i16);
impl_cfrom_both_bounded!(i64 => i8, i16, i32);
impl_cfrom_both_bounded!(i128 => i8, i16, i32, i64);

// unsigned integer -> signed integer
impl_cfrom_upper_bounded!(u8 => i8);
impl_cfrom_upper_bounded!(u16 => i8, i16);
impl_cfrom_upper_bounded!(u32 => i8, i16, i32);
impl_cfrom_upper_bounded!(u64 => i8, i16, i32, i64);
impl_cfrom_upper_bounded!(u128 => i8, i16, i32, i64, i128);

// signed integer -> unsigned integer
impl_cfrom_lower_bounded!(i8 => u8, u16, u32, u64, u128);
impl_cfrom_both_bounded!(i16 => u8);
impl_cfrom_lower_bounded!(i16 => u16, u32, u64, u128);
impl_cfrom_both_bounded!(i32 => u8, u16);
impl_cfrom_lower_bounded!(i32 => u32, u64, u128);
impl_cfrom_both_bounded!(i64 => u8, u16, u32);
impl_cfrom_lower_bounded!(i64 => u64, u128);
impl_cfrom_both_bounded!(i128 => u8, u16, u32, u64);
impl_cfrom_lower_bounded!(i128 => u128);

// usize/isize
impl_cfrom_upper_bounded!(usize => isize);
impl_cfrom_lower_bounded!(isize => usize);

#[cfg(target_pointer_width = "16")]
mod ptr_try_from_impls {
    impl_cfrom_upper_bounded!(usize => u8);
    impl_cfrom_unbounded!(usize => u16, u32, u64, u128);
    impl_cfrom_upper_bounded!(usize => i8, i16);
    impl_cfrom_unbounded!(usize => i32, i64, i128);

    impl_cfrom_both_bounded!(isize => u8);
    impl_cfrom_lower_bounded!(isize => u16, u32, u64, u128);
    impl_cfrom_both_bounded!(isize => i8);
    impl_cfrom_unbounded!(isize => i16, i32, i64, i128);

    rev!(impl_cfrom_upper_bounded, usize => u32, u64, u128);
    rev!(impl_cfrom_lower_bounded, usize => i8, i16);
    rev!(impl_cfrom_both_bounded, usize => i32, i64, i128);

    rev!(impl_cfrom_upper_bounded, isize => u16, u32, u64, u128);
    rev!(impl_cfrom_both_bounded, isize => i32, i64, i128);
}

#[cfg(target_pointer_width = "32")]
mod ptr_try_from_impls {
    impl_cfrom_upper_bounded!(usize => u8, u16);
    impl_cfrom_unbounded!(usize => u32, u64, u128);
    impl_cfrom_upper_bounded!(usize => i8, i16, i32);
    impl_cfrom_unbounded!(usize => i64, i128);

    impl_cfrom_both_bounded!(isize => u8, u16);
    impl_cfrom_lower_bounded!(isize => u32, u64, u128);
    impl_cfrom_both_bounded!(isize => i8, i16);
    impl_cfrom_unbounded!(isize => i32, i64, i128);

    rev!(impl_cfrom_unbounded, usize => u32);
    rev!(impl_cfrom_upper_bounded, usize => u64, u128);
    rev!(impl_cfrom_lower_bounded, usize => i8, i16, i32);
    rev!(impl_cfrom_both_bounded, usize => i64, i128);

    rev!(impl_cfrom_unbounded, isize => u16);
    rev!(impl_cfrom_upper_bounded, isize => u32, u64, u128);
    rev!(impl_cfrom_unbounded, isize => i32);
    rev!(impl_cfrom_both_bounded, isize => i64, i128);
}

#[cfg(target_pointer_width = "64")]
mod ptr_try_from_impls {
    impl_cfrom_upper_bounded!(usize => u8, u16, u32);
    impl_cfrom_unbounded!(usize => u64, u128);
    impl_cfrom_upper_bounded!(usize => i8, i16, i32, i64);
    impl_cfrom_unbounded!(usize => i128);

    impl_cfrom_both_bounded!(isize => u8, u16, u32);
    impl_cfrom_lower_bounded!(isize => u64, u128);
    impl_cfrom_both_bounded!(isize => i8, i16, i32);
    impl_cfrom_unbounded!(isize => i64, i128);

    rev!(impl_cfrom_unbounded, usize => u32, u64);
    rev!(impl_cfrom_upper_bounded, usize => u128);
    rev!(impl_cfrom_lower_bounded, usize => i8, i16, i32, i64);
    rev!(impl_cfrom_both_bounded, usize => i128);

    rev!(impl_cfrom_unbounded, isize => u16, u32);
    rev!(impl_cfrom_upper_bounded, isize => u64, u128);
    rev!(impl_cfrom_unbounded, isize => i32, i64);
    rev!(impl_cfrom_both_bounded, isize => i128);
}