[cmake] CPUInstructionSetFlags.cmake: Check for arm_neon.h when building for ARM.

[librpbyteswap,librptexture] If arm_neon.h isn't available, don't compile
any NEON-optimized functions.

Just in case someone wants to build rom-properties for an ancient ARM
system that was introduced before NEON...

cmake/macros/CPUInstructionSetFlags.cmake

@@ -110,3 +110,10 @@ IF(CPU_i386 OR CPU_amd64)
 		SET(SSE41_FLAG "-msse4.1")
 	ENDIF()
 ENDIF(CPU_i386 OR CPU_amd64)
+
+IF(CPU_arm OR CPU_arm64 OR CPU_arm64ec)
+	# Check for arm_neon.h.
+	# NOTE: Should always be present for arm64, but check anyway.
+	INCLUDE(CheckIncludeFile)
+	CHECK_INCLUDE_FILE("arm_neon.h" HAVE_ARM_NEON_H)
+ENDIF(CPU_arm OR CPU_arm64 OR CPU_arm64ec)

src/librpbyteswap/CMakeLists.txt

@@ -48,8 +48,11 @@ IF(CPU_i386 OR CPU_amd64)
 
 	SET(${PROJECT_NAME}_CPU_SRCS ${${PROJECT_NAME}_MMX_SRCS} ${${PROJECT_NAME}_SSE2_SRCS} ${${PROJECT_NAME}_SSSE3_SRCS})
 ELSEIF(CPU_arm OR CPU_arm64)
-	SET(${PROJECT_NAME}_CPU_SRCS byteswap_neon.c)
+	IF(HAVE_ARM_NEON_H)
+		SET(${PROJECT_NAME}_CPU_SRCS byteswap_neon.c)
+	ENDIF(HAVE_ARM_NEON_H)
 ENDIF()
+UNSET(arch)
 
 # gcc byteswapping intrinsics.
 IF(NOT MSVC)

src/librpbyteswap/byteswap_neon.c

@@ -1,6 +1,6 @@
 /***************************************************************************
  * ROM Properties Page shell extension. (librpbyteswap)                    *
- * byteswap_neon.c: Byteswapping functions.                                *
+ * byteswap_arm64.c: Byteswapping functions.                               *
  * NEON-optimized version.                                                 *
  *                                                                         *
  * Copyright (c) 2008-2025 by David Korth                                  *

src/librpbyteswap/byteswap_rp.h

@@ -39,13 +39,15 @@
 #ifdef RP_CPU_AMD64
 #  define BYTESWAP_ALWAYS_HAS_SSE2 1
 #endif /* RP_CPU_AMD64 */
-#if defined(RP_CPU_ARM) || defined(RP_CPU_ARM64)
+#ifdef HAVE_ARM_NEON_H
-#  include "librpcpuid/cpuflags_arm.h"
+#  if defined(RP_CPU_ARM) || defined(RP_CPU_ARM64)
-#  define BYTESWAP_HAS_NEON 1
+#    include "librpcpuid/cpuflags_arm.h"
-#endif
+#    define BYTESWAP_HAS_NEON 1
-#ifdef RP_CPU_ARM64
+#  endif
-#  define BYTESWAP_ALWAYS_HAS_NEON 1
+#  ifdef RP_CPU_ARM64
-#endif /* RP_CPU_ARM64 */
+#    define BYTESWAP_ALWAYS_HAS_NEON 1
+#  endif /* RP_CPU_ARM64 */
+#endif /* HAVE_ARM_NEON_H */
 
 #if defined(_MSC_VER)
 
@@ -296,12 +298,12 @@ static FORCEINLINE void rp_byte_swap_16_array(uint16_t *ptr, size_t n)
 	if (RP_CPU_arm_HasNEON()) {
 		rp_byte_swap_16_array_neon(ptr, n);
 	} else
-#  endif /* BYTESWAP_HAS_NEON */
+#  endif /* BYTESWAP_HAS_SSE2 */
 	// TODO: MMX-optimized version?
 	{
 		rp_byte_swap_16_array_c(ptr, n);
 	}
-#endif
+#endif /* BYTESWAP_ALWAYS_HAS_SSE2 */
 }
 
 /**
@@ -344,11 +346,11 @@ static FORCEINLINE void rp_byte_swap_32_array(uint32_t *ptr, size_t n)
 	if (RP_CPU_arm_HasNEON()) {
 		rp_byte_swap_32_array_neon(ptr, n);
 	} else
-#  endif /* BYTESWAP_HAS_NEON */
+#  endif /* BYTESWAP_HAS_SSE2 */
 	{
 		rp_byte_swap_32_array_c(ptr, n);
 	}
-#endif
+#endif /* !BYTESWAP_ALWAYS_HAS_SSE2 */
 }
 
 #ifdef __cplusplus

src/librpbyteswap/config.byteswap.h.in

@@ -2,7 +2,7 @@
  * ROM Properties Page shell extension. (librpbyteswap)                    *
  * config.byteswap.h.in: Byteswap intrinsics configuration. (source file)  *
  *                                                                         *
- * Copyright (c) 2016-2024 by David Korth.                                 *
+ * Copyright (c) 2016-2025 by David Korth.                                 *
  * SPDX-License-Identifier: GPL-2.0-or-later                               *
  ***************************************************************************/
 
@@ -11,6 +11,9 @@
 /* Define to 1 if you have the <features.h> header file. */
 #cmakedefine HAVE_FEATURES_H 1
 
+/* Define to 1 if you have the <arm_neon.h> header file. */
+#cmakedefine HAVE_ARM_NEON_H 1
+
 /* Define to 1 if you have __builtin_bswap16(). */
 #cmakedefine HAVE___BUILTIN_BSWAP16 1
 

src/librptexture/CMakeLists.txt

@@ -199,7 +199,9 @@ IF(CPU_i386 OR CPU_amd64)
 		${${PROJECT_NAME}_SSE41_SRCS}
 		)
 ELSEIF(CPU_arm OR CPU_arm64)
-	SET(${PROJECT_NAME}_CPU_SRCS decoder/ImageDecoder_Linear_neon.cpp)
+	IF(HAVE_ARM_NEON_H)
+		SET(${PROJECT_NAME}_CPU_SRCS decoder/ImageDecoder_Linear_neon.cpp)
+	ENDIF(HAVE_ARM_NEON_H)
 ENDIF()
 UNSET(arch)
 

src/librptexture/config.librptexture.h.in

@@ -2,12 +2,15 @@
  * ROM Properties Page shell extension. (librptexture)                     *
  * config.librptexture.h.in: LibRpTexture configuration. (source file)     *
  *                                                                         *
- * Copyright (c) 2016-2023 by David Korth.                                 *
+ * Copyright (c) 2016-2025 by David Korth.                                 *
  * SPDX-License-Identifier: GPL-2.0-or-later                               *
  ***************************************************************************/
 
 #pragma once
 
+/* Define to 1 if you have the <arm_neon.h> header file. */
+#cmakedefine HAVE_ARM_NEON_H 1
+
 /* Define to 1 if librpbase RomFields support should be enabled. */
 #define ENABLE_LIBRPBASE_ROMFIELDS 1
 

src/librptexture/decoder/ImageDecoder_common.hpp

@@ -26,15 +26,19 @@
 #  include "librpcpuid/cpuflags_x86.h"
 #  define IMAGEDECODER_HAS_SSE2 1
 #  define IMAGEDECODER_HAS_SSSE3 1
-#elif defined(RP_CPU_ARM) || defined(RP_CPU_ARM64)
+#elif defined(HAVE_ARM_NEON_H)
-#  include "librpcpuid/cpuflags_arm.h"
+#  if defined(RP_CPU_ARM) || defined(RP_CPU_ARM64)
-#  define IMAGEDECODER_HAS_NEON 1
+#    include "librpcpuid/cpuflags_arm.h"
+#    define IMAGEDECODER_HAS_NEON 1
+#  endif
 #endif
 #ifdef RP_CPU_AMD64
 #  define IMAGEDECODER_ALWAYS_HAS_SSE2 1
 #endif
-#ifdef RP_CPU_ARM64
+#ifdef HAVE_ARM_NEON_H
-#  define IMAGEDECODER_ALWAYS_HAS_NEON 1
+#  ifdef RP_CPU_ARM64
+#    define IMAGEDECODER_ALWAYS_HAS_NEON 1
+#  endif
 #endif
 
 namespace LibRpTexture {