Implement isnan and isinf for WGSL with bitwise operations (#7344)

WGSL doesn't support isnan and isinf, because it assumes that it always uses fast-math and fast-math doesnt' handle NaN as defined in IEEE standard.

The initial implementation used a clever workaround but it stopped working from some point.

This PR implemented isnan and isinf with a bitwise operation, which can be expensive.
But that seems to be an only option at the moment.

2 files changed, 18 insertions, 3 deletions

diff --git a/source/slang/hlsl.meta.slang b/source/slang/hlsl.meta.slang
index 6a3ae63ec..e00108e96 100644
--- a/source/slang/hlsl.meta.slang
+++ b/source/slang/hlsl.meta.slang
@@ -10628,7 +10628,15 @@ bool isinf(T x)
     case spirv:
         return spirv_asm { result:$$bool = OpIsInf $x};
     case wgsl:
-        __intrinsic_asm "($0 > 0x1.fffffep+127f) || ($0 < -0x1.fffffep+127f)";
+        static_assert(T is float, "isnan is implemented only for float type");
+        if (let f = x as float)
+        {
+            let bits = asuint(f);
+            let exp = (bits >> 23) & 0xffu;
+            let frac = bits & 0x7fffffu;
+            return exp == 0xffu && frac == 0u;
+        }
+        return false;
     }
 }
 
@@ -10684,7 +10692,15 @@ bool isnan(T x)
     case spirv:
         return spirv_asm { result:$$bool = OpIsNan $x};
     case wgsl:
-         __intrinsic_asm "$0 != $0";
+        static_assert(T is float, "isnan is implemented only for float type");
+        if (let f = x as float)
+        {
+            let bits = asuint(f);
+            let exp = (bits >> 23) & 0xffu;
+            let frac = bits & 0x7fffffu;
+            return exp == 0xffu && frac != 0u;
+        }
+        return false;
     }
 }
 
diff --git a/tests/expected-failure-github.txt b/tests/expected-failure-github.txt
index 78ae5cf92..0489cafaf 100644
--- a/tests/expected-failure-github.txt
+++ b/tests/expected-failure-github.txt
@@ -14,4 +14,3 @@ tests/language-feature/shader-params/interface-shader-param-ordinary.slang.4 syn
 tests/glsl-intrinsic/shader-subgroup/shader-subgroup-builtin-variables.slang.8 (mtl)
 tests/glsl-intrinsic/shader-subgroup/shader-subgroup-builtin-variables-2.slang.3 (mtl)
 tests/compute/cbuffer-legalize.slang.2 syn (mtl)
-tests/hlsl-intrinsic/classify-float.slang.5 syn (wgpu)