feat: add macro to convert a stride to an index offset

Author: kgryte

lib/node_modules/@stdlib/blas/base/shared/include/stdlib/blas/base/shared.h

@@ -20,5 +20,6 @@
 #define STDLIB_BLAS_BASE_SHARED_H
 
 #include "shared/cblas.h"
+#include "shared/macros.h"
 
 #endif // !STDLIB_BLAS_BASE_SHARED_H

lib/node_modules/@stdlib/blas/base/shared/include/stdlib/blas/base/shared/macros.h

@@ -0,0 +1,47 @@
+/**
+* @license Apache-2.0
+*
+* Copyright (c) 2023 The Stdlib Authors.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+*    http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+#ifndef STDLIB_BLAS_BASE_SHARED_MACROS_H
+#define STDLIB_BLAS_BASE_SHARED_MACROS_H
+
+/*
+* If C++, prevent name mangling so that the compiler emits a binary file having undecorated names, thus mirroring the behavior of a C compiler.
+*/
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+* Macro for converting a stride to an index offset.
+*
+* @param N         number of indexed elements
+* @param stride    index increment
+*
+* @example
+* #include <stdint.h>
+*
+* int64_t offset = STDLIB_BLAS_BASE_STRIDE2OFFSET( 10, -10 );
+* // returns 90
+*/
+#define STDLIB_BLAS_BASE_STRIDE2OFFSET( N, stride ) ( ( (stride) > 0 ) ? 0 : ( 1-(N) ) * (stride) )
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif // !STDLIB_BLAS_BASE_SHARED_MACROS_H