Add getauxval safe implementation

Author: AntoinePrv

include/xsimd/config/xsimd_getauxval.hpp

@@ -0,0 +1,141 @@
+/***************************************************************************
+ * Copyright (c) Johan Mabille, Sylvain Corlay, Wolf Vollprecht and         *
+ * Martin Renou                                                             *
+ * Copyright (c) QuantStack                                                 *
+ * Copyright (c) Serge Guelton                                              *
+ *                                                                          *
+ * Distributed under the terms of the BSD 3-Clause License.                 *
+ *                                                                          *
+ * The full license is in the file LICENSE, distributed with this software. *
+ ***************************************************************************/
+
+#ifndef XSIMD_GETAUXVAL_HPP
+#define XSIMD_GETAUXVAL_HPP
+
+#include "../utils/bits.hpp"
+#include "./xsimd_config.hpp"
+
+#if XSIMD_WITH_LINUX_GETAUXVAL
+#include <sys/auxv.h>
+#endif
+
+namespace xsimd
+{
+    namespace detail
+    {
+        using linux_getauxval_t = unsigned long;
+
+        inline linux_getauxval_t linux_getauxval(linux_getauxval_t type) noexcept;
+
+        /**
+         * Base class for getauxval querying.
+         */
+        template <linux_getauxval_t type, typename A>
+        class linux_auxval : private utils::uint_bitset<A, linux_getauxval_t>
+        {
+            using bitset_t = utils::uint_bitset<A, linux_getauxval_t>;
+
+        public:
+            using aux = A;
+
+            inline static linux_auxval read()
+            {
+                return bitset_t(linux_getauxval(type));
+            }
+
+            /** Create a value which returns false to everything. */
+            constexpr linux_auxval() noexcept = default;
+
+            using bitset_t::all_bits_set;
+        };
+
+        template <typename Traits>
+        using make_auxiliary_val_t = linux_auxval<Traits::type, typename Traits::aux>;
+    }
+
+    /*
+     * Hardware Capabilities Register (HWCAP) for Linux.
+     *
+     * On Linux systems, the kernel exposes some CPU features through the
+     * auxiliary vector, which can be queried via `getauxval(AT_HWCAP)`.
+     * This utility parses such bit values.
+     *
+     * @see https://www.kernel.org/doc/Documentation/arm64/elf_hwcaps.txt
+     */
+    struct linux_hwcap_traits
+    {
+#if XSIMD_WITH_LINUX_GETAUXVAL
+        static constexpr detail::linux_getauxval_t type = AT_HWCAP;
+#else
+        static constexpr detail::linux_getauxval_t type = 0;
+#endif
+
+        enum class aux
+        {
+#if XSIMD_WITH_LINUX_GETAUXVAL
+#if XSIMD_TARGET_ARM64
+            /** Scalable Vector Extension. */
+            sve = HWCAP_SVE,
+#elif XSIMD_TARGET_ARM
+            /** Neon vector extension. */
+            neon = HWCAP_NEON,
+#endif
+#endif
+        };
+    };
+
+    using linux_hwcap = detail::make_auxiliary_val_t<linux_hwcap_traits>;
+
+    /*
+     * Extended Hardware Capabilities Register (HWCAP2) for Linux.
+     *
+     * On Linux systems, the kernel exposes some CPU additional features through the
+     * auxiliary vector, which can be queried via `getauxval(AT_HWCAP2)`.
+     *
+     * @see https://www.kernel.org/doc/Documentation/arm64/elf_hwcaps.txt
+     */
+    struct linux_hwcap2_traits
+    {
+#if XSIMD_WITH_LINUX_GETAUXVAL
+        static constexpr detail::linux_getauxval_t type = AT_HWCAP2;
+#else
+        static constexpr detail::linux_getauxval_t type = 0;
+#endif
+
+        enum class aux
+        {
+#if XSIMD_WITH_LINUX_GETAUXVAL
+#if XSIMD_TARGET_ARM64
+#ifndef HWCAP2_I8MM
+#define HWCAP2_I8MM (1 << 13)
+#endif
+            /** 8 bits integer matrix multiplication. */
+            i8mm = HWCAP2_I8MM,
+#endif
+#endif
+        };
+    };
+
+    using linux_hwcap2 = detail::make_auxiliary_val_t<linux_hwcap2_traits>;
+
+    /********************
+     *  Implementation  *
+     ********************/
+
+    namespace detail
+    {
+#if XSIMD_WITH_LINUX_GETAUXVAL
+        inline linux_getauxval_t linux_getauxval(linux_getauxval_t type) noexcept
+        {
+            return getauxval(type);
+        }
+#else
+        inline linux_getauxval_t linux_getauxval(linux_getauxval_t type) noexcept
+        {
+            return {}; // All bits set to 0
+        }
+#endif
+    }
+}
+
+#endif

include/xsimd/utils/bits.hpp

@@ -55,6 +55,8 @@ namespace xsimd
             /* The enum type whose values name individual bits. */
             using key_type = K;
 
+            constexpr uint_bitset() noexcept = default;
+
             /* Construct from a raw bit pattern. */
             constexpr explicit uint_bitset(storage_type bitset = {}) noexcept
                 : m_bitset(bitset)