Define Base.issubnormal(x:BFloat16)

Author: christiangnrd

src/bfloat16.jl

@@ -63,6 +63,11 @@ Base.exponent_bits(::Type{BFloat16}) = 8
 Base.significand_bits(::Type{BFloat16}) = 7
 Base.signbit(x::BFloat16) = (reinterpret(Unsigned, x) & 0x8000) !== 0x0000
 
+function Base.issubnormal(x::BFloat16)
+    y = reinterpret(Unsigned, x)
+    return (y & exponent_mask(BFloat16) == 0) & (y & significand_mask(BFloat16) != 0)
+end
+
 function Base.significand(x::BFloat16)
     xu = reinterpret(Unsigned, x)
     xs = xu & ~sign_mask(BFloat16)

test/structure.jl

@@ -22,8 +22,15 @@ end
   @test significand(whole) == one(BFloat16)
 
   # subnormal
-  @test significand(reinterpret(BFloat16, 0b0000000000000001)) == one(BFloat16)
-
+  @testset "subnormal" begin
+      allbfs = UInt16(1):typemax(UInt16)
+      res = map(allbfs) do raw
+          bf = reinterpret(BFloat16, raw)
+          issubnormal(bf) == issubnormal(Float32(bf))
+      end
+      @test all(res)
+      @test significand(reinterpret(BFloat16, 0b0000000000000001)) == one(BFloat16)
+  end
   @test frexp(phi) == (BFloat16(0.80859375), 1)
   @test ldexp(BFloat16(0.80859375), 1) == phi