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+# Unstable SIMD module
+
+This module provides helper functionality to build code with SIMD instructions.
+Available since 0.42.0.
+
+**Note**: this module is unstable. It is only provided as a technology
+preview. Its API may change in arbitrary ways between releases or it
+might be removed from Meson altogether.
+
+## Usage
+
+This module is designed for the use case where you have an algorithm
+with one or more SIMD implementation and you choose which one to use
+at runtime.
+
+The module provides one method, `check`, which is used like this:
+
+    rval = simd.check('mysimds',
+      mmx : 'simd_mmx.c',
+      sse : 'simd_sse.c',
+      sse2 : 'simd_sse2.c',
+      sse3 : 'simd_sse3.c',
+      ssse3 : 'simd_ssse3.c',
+      sse41 : 'simd_sse41.c',
+      sse42 : 'simd_sse42.c',
+      avx : 'simd_avx.c',
+      avx2 : 'simd_avx2.c',
+      neon : 'simd_neon.c',
+      compiler : cc)
+
+Here the individual files contain the accelerated versions of the
+functions in question. The `compiler` keyword argument takes the
+compiler you are going to use to compile them. The function returns an
+array with two values. The first value is a bunch of libraries that
+contain the compiled code. Any SIMD code that the compiler can't
+compile (for example, Neon instructions on an x86 machine) are
+ignored. You should pass this value to the desired target using
+`link_with`. The second value is a `configuration_data` object that
+contains true for all the values that were supported. For example if
+the compiler did support sse2 instructions, then the object would have
+`HAVE_SSE2` set to 1.
+
+Generating code to detect the proper instruction set at runtime is
+straightforward. First you create a header with the configuration
+object and then a chooser function that looks like this:
+
+    void (*fptr)(type_of_function_here)  = NULL;
+
+    #if HAVE_NEON
+    if(fptr == NULL && neon_available()) {
+        fptr = neon_accelerated_function;
+    }
+    #endif
+    #if HAVE_AVX2
+    if(fptr == NULL && avx2_available()) {
+        fptr = avx_accelerated_function;
+    }
+    #endif
+
+    ...
+
+    if(fptr == NULL) {
+        fptr = default_function;
+    }
+
+Each source file provides two functions, the `xxx_available` function
+to query whether the CPU currently in use supports the instruction set
+and `xxx_accelerated_function` that is the corresponding accelerated
+implementation.
+
+At the end of this function the function pointer points to the fastest
+available implementation and can be invoked to do the computation.