How Can a Go Function Lack a Body Yet Still Function Correctly?

Function Implementation in Go Assembly

Reading the source code of math/floor.go, you may encounter a puzzling observation:

func Floor(x float64) float64

func floor(x float64) float64 {
    // ...
}

Despite the function definition for Floor being declared, there is no apparent function body for it. This raises the question: are "bodiless" functions permissible in Go's syntax?

In the realm of Go, bodiless functions are indeed a legitimate construct. They serve as placeholders for functions implemented in assembly. Specifically, these assembly implementations are found in the floor_ARCH.s files (for example, AMD64).

As stated in the Go specification:

A function declaration may omit the body. Such a declaration provides the signature for a function implemented outside Go, such as an assembly routine.

So, while the Floor function seems to lack a body in its Go definition, it is in fact implemented in assembly, providing the necessary execution logic.

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