[SR-8484] Using generic math functions fails in Swift 4.2

[swift-ci]

Previous ID	SR-8484
Radar	None
Original Reporter	strike (JIRA User)
Type	Bug

Environment

Xcode 10 beta, Swift 4.2

Additional Detail from JIRA

Votes	0
Component/s	Compiler, Standard Library
Labels	Bug
Assignee	None
Priority	Medium

md5: adc7cdc3c52b5393377de6fa09b0bc78

Issue Description:

Hi!

When using function like lgamma() or tgamma() the compiler complains about

"ambiguous use of tgamma()/lgamma()"

Details can be found here:

https://forums.swift.org/t/float80-math-function/14968/4?u=strike

Regards!

[stephentyrone]

It looks like the c stdlib interfaces for all of the math functions are now being exported as well as the Swift overlay names, e.g. for sin( ) we have all of the following:

sin(Double) -> Double
sin(x: Double) -> Double
sin(x: Float) -> Float
sin(x: Float80) -> Float80
sinf(Float) -> Float
sinl(Float80) -> Float80

In the case of lgamma, the return type of the C libm functions is actually different:

lgamma(Double) -> Double
lgamma(x: Double) -> (Double, Int)
lgamma(x: Float) -> (Float, Int)
lgamma(x: Float80) -> (Float80, Int)
lgammaf(Float) -> Float
lgammal(Float80) -> Float80

which I think causes the bug we're seeing here.