Ouch, we need tests for the tests (and tests for the tests-tests…).
FYI: For a hotfix if you can’t wait for 1.8.1 (and don’t want to downgrade):
julia> import Base:^, @constprop
julia> @constprop :aggressive function ^(x::Float64, y::Float64)
xu = reinterpret(UInt64, x)
xu == reinterpret(UInt64, 1.0) && return 1.0
# Exponents greater than this will always overflow or underflow.
# Note that NaN can pass through this, but that will end up fine.
if !(abs(y)<0x1.8p62)
isnan(y) && return y
y = sign(y)*0x1.8p62
end
yint = unsafe_trunc(Int, y) # This is actually safe since julia freezes the result
y == yint && return @noinline x^yint
2*xu==0 && return abs(y)*Inf*(!(y>0)) # if x==0
x<0 && throw_exp_domainerror(x) # |y| is small enough that y isn't an integer
!isfinite(x) && return x*(y>0 || isnan(x)) # x is inf or NaN
if xu < (UInt64(1)<<52) # x is subnormal
xu = reinterpret(UInt64, x * 0x1p52) # normalize x
xu &= ~sign_mask(Float64)
xu -= UInt64(52) << 52 # mess with the exponent
end
return pow_body(xu, y)
end
^ (generic function with 68 methods)
julia> -10.0^(-Inf)
-0.0
# didn't even need from the PR, for Float64:
julia> @inline function pow_body(x::T, y::T) where T <: Union{Float16, Float32}
return T(exp2(log2(abs(widen(x))) * y))
end
# would need to copy too from PR, for the other, less used, types:
@constprop :aggressive function ^(x::T, y::T) where T <: Union{Float16, Float32}
[..]
return pow_body(x, y)
end
Now, it’s not a very serious bug (or at least “poisoning” with NaN so you will know, not get wrpong non-NaN answers), but it got me thinking, could we have Bugfix.jl with such fixes, that people could opt into? For those who don’t (know of), we still need 1.8.1, and it would mean extra work to fix in two places. Could then Bugfix.jl be a stdlib of Julia, meaning 1.8.1 would just have to reference a certain version. I’m not sure if users of an older version of Julia can upgrade stdlibs.