Merge 5b302fb into 1516c5e

JuliaIntervals · Aug 21, 2019 · d101f0e · d101f0e
2 parents 1516c5e + 5b302fb
commit d101f0e
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diff --git a/src/IntervalArithmetic.jl b/src/IntervalArithmetic.jl
@@ -62,7 +62,7 @@ export
     midpoint_radius, interval_from_midpoint_radius,
     RoundTiesToEven, RoundTiesToAway,
     cancelminus, cancelplus, isunbounded,
-    .., @I_str, ±,
+    .., @I_str, ±, reciprocal_sqrt,
     pow, extended_div,
     setformat, @format
 

diff --git a/src/intervals/functions.jl b/src/intervals/functions.jl
@@ -305,3 +305,12 @@ for f in (:log, :log2, :log10, :log1p)
 
         end
 end
+
+#computes the reciprocal of square root of an Interval
+function reciprocal_sqrt(a::Interval{T}) where T
+    x = sqrt(a)
+    isempty(x) && return emptyinterval(x)
+    x.lo == zero(T) < x.hi && return @round(inv(x.hi), T(Inf))
+    x == zero(x) && return emptyinterval(T)
+    @round(inv(x.hi), inv(x.lo))
+end
diff --git a/test/ITF1788_tests/libieeep1788_tests_elem.jl b/test/ITF1788_tests/libieeep1788_tests_elem.jl
@@ -995,6 +995,20 @@ end
     @test decoration((DecoratedInterval(Interval(-5.0, Inf), dac))^(1//2)) == decoration(DecoratedInterval(Interval(0.0, Inf), trv))
 end
 
+@testset "minimal_rsqrt_test" begin
+    @test reciprocal_sqrt(∅) == ∅
+    @test reciprocal_sqrt(Interval(-Inf, Inf)) == 0 .. Inf
+    @test reciprocal_sqrt(Interval(-Inf, -0x0.0000000000001p-1022)) == ∅
+    @test reciprocal_sqrt(Interval(-1.0, 1.0)) == 1.0 .. Inf
+    @test reciprocal_sqrt(Interval(0.0, 1.0)) == 1.0 .. Inf
+    @test reciprocal_sqrt(Interval(-0.0, 1.0)) == 1.0 .. Inf
+    @test reciprocal_sqrt(Interval(-5.0, 25.0)) == 0.2 .. Inf
+    @test reciprocal_sqrt(Interval(0.0, 25.0)) == 0.2 .. Inf
+    @test reciprocal_sqrt(Interval(-0.0, 25.0)) == 0.2 .. Inf
+    @test reciprocal_sqrt(Interval(-5.0, Inf)) == 0.0 .. Inf
+    @test reciprocal_sqrt(Interval(4.0, 25.0)) == 0.2 .. 0.5
+end
+
 @testset "minimal_fma_test" begin
     @test fma(∅, ∅, ∅) == ∅
     @test fma(Interval(-1.0, 1.0), ∅, ∅) == ∅