SpirvShader: Implement GLSLstd450Log2

src/Pipeline/SpirvShader.cpp

@@ -3441,7 +3441,11 @@ namespace sw
 		}
 		case GLSLstd450Log2:
 		{
-			UNIMPLEMENTED("GLSLstd450Log2");
+			auto val = GenericValue(this, routine, insn.word(5));
+			for (auto i = 0u; i < type.sizeInComponents; i++)
+			{
+				dst.move(i, Log2(val.Float(i)));
+			}
 			break;
 		}
 		case GLSLstd450Sqrt:

src/Reactor/LLVMReactor.cpp

@@ -570,6 +570,7 @@ namespace rr
 			func_.emplace("expf", reinterpret_cast<void*>(expf));
 			func_.emplace("logf", reinterpret_cast<void*>(logf));
 			func_.emplace("exp2f", reinterpret_cast<void*>(exp2f));
+			func_.emplace("log2f", reinterpret_cast<void*>(log2f));
 
 #ifdef __APPLE__
 			// LLVM uses this function on macOS for tan.
@@ -3203,6 +3204,12 @@ namespace rr
 		return RValue<Float4>(V(::builder->CreateCall(func, { V(v.value) })));
 	}
 
+	RValue<Float4> Log2(RValue<Float4> v)
+	{
+		auto func = llvm::Intrinsic::getDeclaration(::module, llvm::Intrinsic::log2, { T(Float4::getType()) } );
+		return RValue<Float4>(V(::builder->CreateCall(func, { V(v.value) })));
+	}
+
 	Type *Float4::getType()
 	{
 		return T(llvm::VectorType::get(T(Float::getType()), 4));

src/Reactor/Reactor.hpp

@@ -2228,6 +2228,7 @@ namespace rr
 	RValue<Float4> Exp(RValue<Float4> x);
 	RValue<Float4> Log(RValue<Float4> x);
 	RValue<Float4> Exp2(RValue<Float4> x);
+	RValue<Float4> Log2(RValue<Float4> x);
 
 	template<class T>
 	class Pointer : public LValue<Pointer<T>>