mul_add.rs - source
Description: Source of the Rust file `/Users/erlendbasso/.cargo/registry/src/github.com-1ecc6299db9ec823/num-traits-0.2.15/src/ops/mul_add.rs`.
Keywords: rust, rustlang, rust-lang

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    /// Fused multiply-add. Computes `(self * a) + b` with only one rounding
    /// error, yielding a more accurate result than an unfused multiply-add.
    ///
    /// Using `mul_add` can be more performant than an unfused multiply-add if
    /// the target architecture has a dedicated `fma` CPU instruction.
    ///
    /// Note that `A` and `B` are `Self` by default, but this is not mandatory.
    ///
    /// # Example
    ///
    /// ```
    /// use std::f32;
    ///
    /// let m = 10.0_f32;
    /// let x = 4.0_f32;
    /// let b = 60.0_f32;
    ///
    /// // 100.0
    /// let abs_difference = (m.mul_add(x, b) - (m*x + b)).abs();
    ///
    /// assert!(abs_difference <= 100.0 * f32::EPSILON);
    /// ```
    pub trait MulAdd<A = Self, B = Self> {
        /// The resulting type after applying the fused multiply-add.
        type Output;

        /// Performs the fused multiply-add operation.
        fn mul_add(self, a: A, b: B) -> Self::Output;
    }

    /// The fused multiply-add assignment operation.
    pub trait MulAddAssign<A = Self, B = Self> {
        /// Performs the fused multiply-add operation.
        fn mul_add_assign(&mut self, a: A, b: B);
    }

    #[cfg(any(feature = "std", feature = "libm"))]
    impl MulAdd<f32, f32> for f32 {
        type Output = Self;

        #[inline]
        fn mul_add(self, a: Self, b: Self) -> Self::Output {
            <Self as ::Float>::mul_add(self, a, b)
        }
    }

    #[cfg(any(feature = "std", feature = "libm"))]
    impl MulAdd<f64, f64> for f64 {
        type Output = Self;

        #[inline]
        fn mul_add(self, a: Self, b: Self) -> Self::Output {
            <Self as ::Float>::mul_add(self, a, b)
        }
    }

    macro_rules! mul_add_impl {
        ($trait_name:ident for $($t:ty)*) => {$(
            impl $trait_name for $t {
                type Output = Self;

                #[inline]
                fn mul_add(self, a: Self, b: Self) -> Self::Output {
                    (self * a) + b
                }
            }
        )*}
    }

    mul_add_impl!(MulAdd for isize usize i8 u8 i16 u16 i32 u32 i64 u64);
    #[cfg(has_i128)]
    mul_add_impl!(MulAdd for i128 u128);

    #[cfg(any(feature = "std", feature = "libm"))]
    impl MulAddAssign<f32, f32> for f32 {
        #[inline]
        fn mul_add_assign(&mut self, a: Self, b: Self) {
            *self = <Self as ::Float>::mul_add(*self, a, b)
        }
    }

    #[cfg(any(feature = "std", feature = "libm"))]
    impl MulAddAssign<f64, f64> for f64 {
        #[inline]
        fn mul_add_assign(&mut self, a: Self, b: Self) {
            *self = <Self as ::Float>::mul_add(*self, a, b)
        }
    }

    macro_rules! mul_add_assign_impl {
        ($trait_name:ident for $($t:ty)*) => {$(
            impl $trait_name for $t {
                #[inline]
                fn mul_add_assign(&mut self, a: Self, b: Self) {
                    *self = (*self * a) + b
                }
            }
        )*}
    }

    mul_add_assign_impl!(MulAddAssign for isize usize i8 u8 i16 u16 i32 u32 i64 u64);
    #[cfg(has_i128)]
    mul_add_assign_impl!(MulAddAssign for i128 u128);

    #[cfg(test)]
    mod tests {
        use super::*;

        #[test]
        fn mul_add_integer() {
            macro_rules! test_mul_add {
                ($($t:ident)+) => {
                    $(
                        {
                            let m: $t = 2;
                            let x: $t = 3;
                            let b: $t = 4;

                            assert_eq!(MulAdd::mul_add(m, x, b), (m*x + b));
                        }
                    )+
                };
            }

            test_mul_add!(usize u8 u16 u32 u64 isize i8 i16 i32 i64);
        }

        #[test]
        #[cfg(feature = "std")]
        fn mul_add_float() {
            macro_rules! test_mul_add {
                ($($t:ident)+) => {
                    $(
                        {
                            use core::$t;

                            let m: $t = 12.0;
                            let x: $t = 3.4;
                            let b: $t = 5.6;

                            let abs_difference = (MulAdd::mul_add(m, x, b) - (m*x + b)).abs();

                            assert!(abs_difference <= 46.4 * $t::EPSILON);
                        }
                    )+
                };
            }

            test_mul_add!(f32 f64);
        }
    }