Add a expm1 method for Float16 for older Julia versions

src/distrs/tdist.jl

@@ -49,13 +49,24 @@ tdistinvcdf(ν::Real, p::Real) = tdistinvcdf(map(float, promote(ν, p))...)
 
 tdistinvccdf(ν::Real, p::Real) = -tdistinvcdf(ν, p)
 
+if VERSION < v"1.7.0-beta1"
+ function _expm1(x::Float16)
+ if -0.2 < x < 0.1
+ return @evalpoly(x, Float16(0), Float16(1), Float16(1/2), Float16(1/6), Float16(1/24), Float16(1/120))
+ else
+ return exp(x) - 1
+ end
+ end
+end
+_expm1(x::Number) = expm1(x)
+
 function tdistinvlogcdf(ν::T, logp::T) where T<:Real
  if isinf(ν)
  return norminvlogcdf(logp)
  elseif logp < -log(2)
  return -sqrt(fdistinvlogccdf(one(ν), ν, logp + log(2*one(logp))))
  else
- sqrt(fdistinvccdf(one(ν), ν, -2*expm1(logp)))
+ sqrt(fdistinvccdf(one(ν), ν, -2*_expm1(logp)))
  end
 end
 tdistinvlogcdf(ν::Real, logp::Real) = tdistinvlogcdf(map(float, promote(ν, logp))...)