What is functionality of Pointwise Equal, Pointwise less than, and Pointwise greater in Swift?

Question

While reading the Swift Programming Language book by Apple, I came across Pointwise equal, Pointwise less than and Pointwise greater than operators. Reference: https://developer.apple.com/documentation/swift/swift_standard_library/operator_declarations

.== Pointwise equal

.!= Pointwise not equal

I couldn't find any explanation and example on when to use these. What is the functionality of these operators?

Answer 1

The operators are part of protocol SIMD, the protocol to which the “SIMD vector types” conform.

They were introduced in Swift 5 with SE-0229. From that proposal:

Let's discuss Masks. SIMDs are Equatable, so they have the == and != operators, but they also provide the "pointwise comparison" .== and .!= operators, which compare the lanes of two vectors, and produce a Mask, which is a vector of boolean values. Each lane of the mask is either true or false, depending on the result of comparing the values in the corresponding lanes. An example:

(swift) let x = SIMD4<Int>(1,2,3,4)
// x : SIMD4<Int> = SIMD4<Int>(1, 2, 3, 4)
(swift) let y = SIMD4<Int>(3,2,1,0)
// y : SIMD4<Int> = SIMD4<Int>(3, 2, 1, 0)
(swift) x .== y
// r0 : SIMDMask<SIMD4<Int.SIMDMaskScalar>> = SIMDMask<SIMD4<Int>>(false, true, false, false)

here, the second lane is true, because 2 == 2, while all other lanes are false because the elements of x and y in those lanes are not equal.

Extract from protocol SIMD:

A SIMD vector of a fixed number of elements.

static func .== (Self, Self) -> SIMDMask<Self.MaskStorage>
// Returns a vector mask with the result of a pointwise equality comparison.

static func .> (Self, Self) -> SIMDMask<Self.MaskStorage>
// Returns a vector mask with the result of a pointwise greater than comparison.

Another example:

import simd

let x = SIMD3<Float>(1.0, 2.0, 3.0)
let y = SIMD3<Float>(3.0, 2.0, 1.0)

print(x .== y) // SIMDMask<SIMD3<Int32>>(false, true, false)
print(x .!= y) // SIMDMask<SIMD3<Int32>>(true, false, true)
print(x .< y)  // SIMDMask<SIMD3<Int32>>(true, false, false)