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fix overflow and undeflow for @fastmath exp #42747

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Merged
merged 3 commits into from
Oct 22, 2021
Merged

fix overflow and undeflow for @fastmath exp #42747

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fdbae11
fix overflow and undeflow for @fastmath exp
oscardssmith Oct 21, 2021
6c9e2b9
fixed
oscardssmith Oct 21, 2021
e8d5678
add tests
oscardssmith Oct 22, 2021
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4 changes: 4 additions & 0 deletions base/special/exp.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -254,6 +254,8 @@ end
end
@inline function exp_impl_fast(x::Float64, base)
T = Float64
x >= MAX_EXP(base, T) && return Inf
x <= -SUBNORM_EXP(base, T) && return 0.0
N_float = muladd(x, LogBo256INV(base, T), MAGIC_ROUND_CONST(T))
N = reinterpret(UInt64, N_float) % Int32
N_float -= MAGIC_ROUND_CONST(T) #N_float now equals round(x*LogBo256INV(base, T))
Expand Down Expand Up @@ -288,6 +290,8 @@ end

@inline function exp_impl_fast(x::Float32, base)
T = Float32
x >= MAX_EXP(base, T) && return Inf32
x <= -SUBNORM_EXP(base, T) && return 0f0
N_float = round(x*LogBINV(base, T))
N = unsafe_trunc(Int32, N_float)
r = muladd(N_float, LogBU(base, T), x)
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10 changes: 10 additions & 0 deletions test/fastmath.jl
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Expand Up @@ -249,3 +249,13 @@ end
@test (@fastmath "a" * "b") == "ab"
@test (@fastmath "a" ^ 2) == "aa"
end


@testset "exp overflow and underflow" begin
for T in (Float32,Float64)
for func in (@fastmath exp2,exp,exp10)
@test func(T(2000)) == T(Inf)
@test func(T(-2000)) == T(0)
end
end
end