use int::{Int, LargeInt};

trait Ashl: Int + LargeInt {
    /// Returns `a << b`, requires `b < Self::BITS`
    fn ashl(self, offset: u32) -> Self
    where
        Self: LargeInt<HighHalf = <Self as LargeInt>::LowHalf>,
    {
        let half_bits = Self::BITS / 2;
        if offset & half_bits != 0 {
            Self::from_parts(Int::ZERO, self.low() << (offset - half_bits))
        } else if offset == 0 {
            self
        } else {
            Self::from_parts(
                self.low() << offset,
                (self.high() << offset) | (self.low() >> (half_bits - offset)),
            )
        }
    }
}

impl Ashl for u64 {}
impl Ashl for u128 {}

trait Ashr: Int + LargeInt {
    /// Returns arithmetic `a >> b`, requires `b < Self::BITS`
    fn ashr(self, offset: u32) -> Self
    where
        Self: LargeInt<LowHalf = <<Self as LargeInt>::HighHalf as Int>::UnsignedInt>,
    {
        let half_bits = Self::BITS / 2;
        if offset & half_bits != 0 {
            Self::from_parts(
                (self.high() >> (offset - half_bits)).unsigned(),
                self.high() >> (half_bits - 1),
            )
        } else if offset == 0 {
            self
        } else {
            let high_unsigned = self.high().unsigned();
            Self::from_parts(
                (high_unsigned << (half_bits - offset)) | (self.low() >> offset),
                self.high() >> offset,
            )
        }
    }
}

impl Ashr for i64 {}
impl Ashr for i128 {}

trait Lshr: Int + LargeInt {
    /// Returns logical `a >> b`, requires `b < Self::BITS`
    fn lshr(self, offset: u32) -> Self
    where
        Self: LargeInt<HighHalf = <Self as LargeInt>::LowHalf>,
    {
        let half_bits = Self::BITS / 2;
        if offset & half_bits != 0 {
            Self::from_parts(self.high() >> (offset - half_bits), Int::ZERO)
        } else if offset == 0 {
            self
        } else {
            Self::from_parts(
                (self.high() << (half_bits - offset)) | (self.low() >> offset),
                self.high() >> offset,
            )
        }
    }
}

impl Lshr for u64 {}
impl Lshr for u128 {}

intrinsics! {
    #[maybe_use_optimized_c_shim]
    #[arm_aeabi_alias = __aeabi_llsl]
    pub extern "C" fn __ashldi3(a: u64, b: u32) -> u64 {
        a.ashl(b)
    }

    pub extern "C" fn __ashlti3(a: u128, b: u32) -> u128 {
        a.ashl(b)
    }

    #[maybe_use_optimized_c_shim]
    #[arm_aeabi_alias = __aeabi_lasr]
    pub extern "C" fn __ashrdi3(a: i64, b: u32) -> i64 {
        a.ashr(b)
    }

    pub extern "C" fn __ashrti3(a: i128, b: u32) -> i128 {
        a.ashr(b)
    }

    #[maybe_use_optimized_c_shim]
    #[arm_aeabi_alias = __aeabi_llsr]
    pub extern "C" fn __lshrdi3(a: u64, b: u32) -> u64 {
        a.lshr(b)
    }

    pub extern "C" fn __lshrti3(a: u128, b: u32) -> u128 {
        a.lshr(b)
    }
}

u128_lang_items! {
    #[lang = "i128_shl"]
    pub fn rust_i128_shl(a: i128, b: u32) -> i128 {
        __ashlti3(a as _, b) as _
    }
    #[lang = "i128_shlo"]
    pub fn rust_i128_shlo(a: i128, b: u128) -> (i128, bool) {
        (rust_i128_shl(a, b as _), b >= 128)
    }
    #[lang = "u128_shl"]
    pub fn rust_u128_shl(a: u128, b: u32) -> u128 {
        __ashlti3(a, b)
    }
    #[lang = "u128_shlo"]
    pub fn rust_u128_shlo(a: u128, b: u128) -> (u128, bool) {
        (rust_u128_shl(a, b as _), b >= 128)
    }

    #[lang = "i128_shr"]
    pub fn rust_i128_shr(a: i128, b: u32) -> i128 {
        __ashrti3(a, b)
    }
    #[lang = "i128_shro"]
    pub fn rust_i128_shro(a: i128, b: u128) -> (i128, bool) {
        (rust_i128_shr(a, b as _), b >= 128)
    }
    #[lang = "u128_shr"]
    pub fn rust_u128_shr(a: u128, b: u32) -> u128 {
        __lshrti3(a, b)
    }
    #[lang = "u128_shro"]
    pub fn rust_u128_shro(a: u128, b: u128) -> (u128, bool) {
        (rust_u128_shr(a, b as _), b >= 128)
    }
}