NoDenormals

include/mostly_harmless/CMakeLists.txt

@@ -25,5 +25,6 @@ set(MOSTLYHARMLESS_HEADERS
         ${CMAKE_CURRENT_SOURCE_DIR}/utils/mostlyharmless_Directories.h
         ${CMAKE_CURRENT_SOURCE_DIR}/utils/mostlyharmless_OnScopeExit.h
         ${CMAKE_CURRENT_SOURCE_DIR}/utils/mostlyharmless_Proxy.h
+        ${CMAKE_CURRENT_SOURCE_DIR}/utils/mostlyharmless_NoDenormals.h
         ${PLATFORM_HEADERS}
         PARENT_SCOPE)

include/mostly_harmless/utils/mostlyharmless_NoDenormals.h

@@ -0,0 +1,30 @@
+//
+// Created by Syl Morrison on 21/03/2025.
+//
+
+#ifndef MOSTLYHARMLESS_NODENORMALS_H
+#define MOSTLYHARMLESS_NODENORMALS_H
+#include <memory>
+namespace mostly_harmless::utils {
+    /**
+        \brief RAII mechanism to disable denormals while an instance of this class is alive.
+        Supports SSE or NEON instruction sets, will have no effect if neither of those are present.
+        Goes without saying, but doesn't allocate (I deliberately didn't use pImpl for this reason)
+    */
+    class NoDenormals final {
+    public:
+        /**
+         * Disables denormals on construction, by setting FTZ (and DAZ in SSE)
+         */
+        NoDenormals();
+
+        /**
+         * Resets the FTZ / DAZ bits to their original states
+         */
+        ~NoDenormals() noexcept;
+
+    private:
+        std::variant<std::uint8_t, std::uintptr_t> m_controlFlag;
+    };
+} // namespace mostly_harmless::utils
+#endif // MOSTLYHARMLESS_NODENORMALS_H

source/CMakeLists.txt

@@ -3,7 +3,7 @@ if (APPLE)
             ${CMAKE_CURRENT_SOURCE_DIR}/gui/platform/mostlyharmless_GuiHelpersMacOS.mm
             ${CMAKE_CURRENT_SOURCE_DIR}/utils/platform/mostlyharmless_DirectoriesMacOS.mm
     )
-else()
+else ()
     set(PLATFORM_SOURCES
             ${CMAKE_CURRENT_SOURCE_DIR}/utils/platform/mostlyharmless_DirectoriesWindows.cpp
     )
@@ -24,6 +24,7 @@ set(MOSTLYHARMLESS_SOURCES
         ${CMAKE_CURRENT_SOURCE_DIR}/utils/mostlyharmless_TaskThread.cpp
         ${CMAKE_CURRENT_SOURCE_DIR}/utils/mostlyharmless_Timer.cpp
         ${CMAKE_CURRENT_SOURCE_DIR}/utils/mostlyharmless_OnScopeExit.cpp
+        ${CMAKE_CURRENT_SOURCE_DIR}/utils/mostlyharmless_NoDenormals.cpp
         ${PLATFORM_SOURCES}
         PARENT_SCOPE)
 message(STATUS ${MOSTLYHARMLESS_PLATFORM_SOURCES})

source/mostlyharmless_PluginBase.cpp

@@ -4,7 +4,9 @@
 #include <mostly_harmless/mostlyharmless_PluginBase.h>
 #include <mostly_harmless/utils/mostlyharmless_Macros.h>
 #include <mostly_harmless/audio/mostlyharmless_AudioHelpers.h>
+#include <mostly_harmless/utils/mostlyharmless_NoDenormals.h>
 #include <clap/helpers/plugin.hxx>
+
 namespace mostly_harmless::internal {
     PluginBase::PluginBase(const clap_host* host) : clap::helpers::Plugin<clap::helpers::MisbehaviourHandler::Ignore, clap::helpers::CheckingLevel::Maximal>(&getDescriptor(), host) {
         MH_LOG("PROC: Creating plugin instance...");
@@ -46,6 +48,8 @@ namespace mostly_harmless::internal {
     }
 
     clap_process_status PluginBase::process(const clap_process* processContext) noexcept {
+
+        [[maybe_unused]] utils::NoDenormals stopDenormals;
         if (processContext->audio_outputs_count == 0) {
             return CLAP_PROCESS_SLEEP;
         }

source/utils/mostlyharmless_NoDenormals.cpp

@@ -0,0 +1,32 @@
+//
+// Created by Syl Morrison on 21/03/2025.
+//
+#include <mostly_harmless/utils/mostlyharmless_NoDenormals.h>
+#include <cstdint>
+namespace mostly_harmless::utils {
+#if defined(__SSE__) || defined(_M_X64)
+#include <xmmintrin.h>
+#endif
+    NoDenormals::NoDenormals() {
+#if defined(__SSE__) || defined(_M_X64)
+            m_controlFlag = _mm_getcsr();
+            constexpr static auto FTZ_AND_DAZ = 0x8040;
+            _mm_setcsr(std::get<std::uint8_t>(m_controlFlag) | FTZ_AND_DAZ);
+#elif defined(__ARM_NEON) || defined(__ARM_NEON__)
+            constexpr static auto FTZ = 0x01000000U;
+            uintptr_t asmStatus;
+            asm volatile("mrs %0, fpcr" : "=r"(asmStatus));
+            m_controlFlag = asmStatus = asmStatus | FTZ;
+            asm volatile("msr fpcr, %0" : : "ri"(asmStatus));
+#endif
+    }
+
+    NoDenormals::~NoDenormals() noexcept  {
+#if defined(__SSE__) || defined(_M_X64)
+            _mm_setcsr(std::get<std::uint8_t>(m_controlFlag));
+#elif defined(__ARM_NEON) || defined(__ARM_NEON__)
+            uintptr_t asmStatus = std::get<std::uintptr_t>(m_controlFlag);
+            asm volatile("msr fpcr, %0" : : "ri"(asmStatus));
+#endif
+    }
+}