Tinkered with SIMD operations in Swift

Working on PRs [string] SIMD-izes internal func in StringCreate.swift and on SIMD variant of PR [stdlib] Add to Unsafe[Mutable]RawBufferPointer implementation of _custom[Last]IndexOfEquatableElement explained in post I have found that Swift’s implementation of SIMD misses operations for checking if SIMD vector includes particular scalar. At the same time, simd implementation in Objective-C has simd_any and simd_all. These is poor documented in Apple documentation. These operations allow check not only presence of some scalar but allow use conditions like

if (simd_any(x < 0)) {
    // executed if any lane of x
    // contains a negative value.
}

if (simd_all(x == 0)) {
    // executed if every lane of x
    // contains zero.
 }

Implementing these operations in Swift would become reasonable Swift proposal extending proposal SIMD Vectors which introduced SIMD.

Proposal makes possible above mentioned operations only on two steps:

if (SIMD4<Int>(1,2,-3,4) .< 0) != SIMDMask<SIMD4<Int>>(repeating: false) {
    // executed if any lane of vector
    // contains a negative value.
    print("There's a lane with negative value.")
} else {
    print("All lanes have non-negative values.")
}

if (SIMD4<Int>(-1,-2,-3,-4) .< 0) == SIMDMask<SIMD4<Int>>(repeating: true) {
    // executed if every lane of vector
    // contains a negative value.
    print("All lanes have negative values.")
} else {
    print("There's a lane with non-negative value.")
}

May be it does make sense defining operations like ∀< for all and ∃< for any. Math symbol ∀ means ‘all’, and ∃ - ‘there exists’. These operations could be defined like:

infix operator ∀<: ComparisonPrecedence // all
infix operator ∃<: ComparisonPrecedence // any

extension SIMD where Scalar: Comparable {
    /// Returns a boolean if all lane contains value less then provided scalar.
    public static func ∀<(vector: Self, scalar: Scalar) -> Bool {
        for index in vector.indices where !(vector[index] < scalar) {
            return false
        }
        return true

        /// Alternative implementation in terms of vector operations
        return (vector .< scalar) == SIMDMask(repeating: true)
    }

    /// Returns a boolean if any lane contains value less then provided scalar.
    public static func ∃<(vector: Self, scalar: Scalar) -> Bool {
        for index in vector.indices where vector[index] < scalar {
            return true
        }
        return false

        /// Alternative implementation in terms of vector operations
        return (vector .< scalar) != SIMDMask(repeating: false)
    }
}

With such operations comparisons from snippets above become one step and much more readable:

if SIMD4<Int>(1,2,-3,4) ∃< 0 {
    // executed if any lane of vector
    // contains a negative value.
    print("There's a lane with negative value.")
} else {
    print("All lanes have non-negative values.")
}

if SIMD4<Int>(-1,-2,-3,-4) ∀< 0 {
    // executed if every lane of vector
    // contains a negative value.
    print("All lanes have negative values.")
} else {
    print("There's a lane with non-negative value.")
}

Fuuuuuuuuuck. SIMDVector.swift defines global functions any and all on SIMDMask argument which make possible what is needed. Why SIMD neither SIMD proposal nor any post/article I have read mentions these important functions!?

if all(SIMD4<Int>(-1,-2,-3,-4) .< 0) {
    // executed if any lane of vector
    // contains a negative value.
    print("There's a lane with negative value.")
}

if any(SIMD4<Int>(1,2,-3,4) .< 0) {
    // executed if any lane of vector
    // contains a negative value.
    print("There's a lane with negative value.")
}