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[DO NOT MERGE] make sinpi/cospi return Int #35823

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[DO NOT MERGE] make sinpi/cospi return Int #35823

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4 changes: 2 additions & 2 deletions base/special/trig.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -927,8 +927,8 @@ function sincospi(x::T) where T<:Rational
end
end

sinpi(x::Integer) = x >= 0 ? zero(float(x)) : -zero(float(x))
cospi(x::Integer) = isodd(x) ? -one(float(x)) : one(float(x))
sinpi(x::T) where {T<:Integer} = zero(signed(T))
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I think it's fine if sinpi and cospi have different return types, so that some computations remain Unsigned if all their underlying functions allow it. If someone plugs results of sinpi and cospi together, type promotion will fix that difference.

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Is the optimizer smart enough to remove the branch for toes where zero=-zero?

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I think I don't know what you mean. For integers there (usually?) is no difference between +0 and -0.

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I still think sinpi and cospi are too closely related to return different types. They are often used together, for example in cispi #35792 and sincospi #35816. Type promotion doesn't address all those problems, since the latter would produce an inhomogenous typed tuple and could produce quite unexpected and hard to debug results in edge cases. What would be the benefit of returning unsigned integers instead?

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@jonas-schulze jonas-schulze May 12, 2020 •
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It seems like type promotion as quiete preservative with UInts already, so I'm ok with your solution.

julia> typeof(UInt8(10) - Int8(2)) == typeof(UInt8(10) + Int8(2)) == UInt8
true

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@PallHaraldsson PallHaraldsson May 18, 2020 •
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[Would we only merge this for purists, and this method not ever used in practice, as "useless"?]
@jonas-schulze, Julia assumes all platforms use two's complement integers (like current C++, unlike C and older C++), https://en.wikipedia.org/wiki/Ones'_complement is very outdated, but given such a type (and with Julia you could make one, I'm not sure why you would), I'm not even sure if it should do the similar to floats:

julia> sin(-0.0)
-0.0

julia> sin(-0.0) == sin(-0)  # defined true, even with returning opposite signs (as -0 = 0):
true

[Does -0 == +0 usually, on the ancient one's complement platforms?]

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@simeonschaub simeonschaub May 18, 2020 •
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@PallHaraldsson That does sound like a very hypothetical example to me. I am not aware of Julia running on any non-two's-complement architectures. This assumption is also made throughout all of Base, so if there was such a platform, these would probably be the least of our worries.

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Right, I was just addressing his "(usually?) is no difference between +0 and -0." I'm not worried about any of this, and would be ok with status quo, just like division returns floats (as natural at least there). Your change would work with all integer types, I know already defined, e.g. BitIntegers.jl, and all future types hopefully (like if someone made up one's complement on two-complements architecture).

cospi(x::T) where {T<:Integer} = isodd(x) ? -one(signed(T)) : one(signed(T))
sincospi(x::Integer) = (sinpi(x), cospi(x))
sinpi(x::Real) = sinpi(float(x))
cospi(x::Real) = cospi(float(x))
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