Function without body

[angan...@gmail.com]

The language specification says:

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

I can understand the abs.go list the function as `func Abs(x float64) float64` without body because there are three files which implemented this function: abs_386.s, abs_arm.s, abs_amd64.s. 

But there is also a function in abs.go with the signature `func abs(x float64) float64` which is not exported, and I don't know where it is used.

Can someone please explain this for me? Thanks

[angan...@gmail.com]

I mean this Go source file from math package: https://code.google.com/p/go/source/browse/src/pkg/math/abs.go

[andrey mirtchovski]

read the description for the CL that introduced it:

https://code.google.com/p/go/source/detail?r=af839530a31e

specifically that assembly implementations for unsupported
architectures may jump back to the pure go implementation.

i don't think (only briefly checked) there are any architectures that
aren't implementing all those basic functions in assembly, but that
doesn't mean there won't be others in the future.

[Dave Cheney]

Some of the crypto/shaXXX implementations use a pure Go impl for 32bit platforms, they could be a good place to look.

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[Caleb Doxsey]

Here's another example:

http://golang.org/src/pkg/math/atan2_arm.s

Go is case sensitive so Abs is different from abs.

For more info about assembly I have a full walkthrough here:

http://www.doxsey.net/blog/go-and-assembly

[angan...@gmail.com]

Thank you all for these good explanations. I'm very happy that Golang community has so many helpful and kindness experts here to help us.