Merge pull request #95 from JuliaMath/teh/float16

Prevent overflow when converting from Float16

Author: timholy

src/normed.jl

@@ -50,6 +50,11 @@ function _convert(::Type{U}, ::Type{T}, x) where {U <: Normed,T}
     (0 <= y) & (y <= typemax(T)) || throw_converterror(U, x)
     U(_unsafe_trunc(T, y), 0)
 end
+# Prevent overflow (https://discourse.julialang.org/t/saving-greater-than-8-bit-images/6057)
+_convert(::Type{U}, ::Type{T}, x::Float16) where {U <: Normed,T} =
+    _convert(U, T, Float32(x))
+_convert(::Type{U}, ::Type{UInt128}, x::Float16) where {U <: Normed} =
+    _convert(U, UInt128, Float32(x))
 function _convert(::Type{U}, ::Type{UInt128}, x) where {U <: Normed}
     y = round(rawone(U)*x)   # for UInt128, we can't widen
     (0 <= y) & (y <= typemax(UInt128)) & (x <= Float64(typemax(U))) || throw_converterror(U, x)
@@ -59,6 +64,7 @@ end
 rem(x::T, ::Type{T}) where {T <: Normed} = x
 rem(x::Normed, ::Type{T}) where {T <: Normed} = reinterpret(T, _unsafe_trunc(rawtype(T), round((rawone(T)/rawone(x))*reinterpret(x))))
 rem(x::Real, ::Type{T}) where {T <: Normed} = reinterpret(T, _unsafe_trunc(rawtype(T), round(rawone(T)*x)))
+rem(x::Float16, ::Type{T}) where {T <: Normed} = rem(Float32(x), T)  # avoid overflow
 
 # convert(::Type{AbstractFloat}, x::Normed) = convert(floattype(x), x)
 float(x::Normed) = convert(floattype(x), x)

test/normed.jl

@@ -300,3 +300,7 @@ for T in (Normed{UInt8,8}, Normed{UInt8,6},
     @test isa(a, Array{T,2})
     @test size(a) == (3,5)
 end
+
+# Overflow with Float16
+@test N0f16(Float16(1.0)) === N0f16(1.0)
+@test Float16(1.0) % N0f16 === N0f16(1.0)

test/runtests.jl

@@ -1,8 +1,8 @@
 using FixedPointNumbers, Base.Test
 
+@test isempty(detect_ambiguities(FixedPointNumbers, Base, Core))
+
 for f in ["normed.jl", "fixed.jl"]
     println("Testing $f")
     include(f)
 end
-
-@test isempty(detect_ambiguities(FixedPointNumbers, Base, Core))