+
+;;; User visible extension
+(declaim (ftype (function (simple-array) (values (simple-array * (*)) &optional))
+ simple-array-vector))
+(defun simple-array-vector (array)
+ "Returns the one-dimensional SIMPLE-ARRAY corresponding to ARRAY.
+
+The ARRAY must be a SIMPLE-ARRAY. If ARRAY is multidimensional, returns the
+underlying one-dimensional SIMPLE-ARRAY which shares storage with ARRAY.
+Otherwise returns ARRAY.
+
+Currently in SBCL a multidimensional SIMPLE-ARRAY has an underlying
+one-dimensional SIMPLE-ARRAY, which holds the data in row major order. This
+function provides access to that vector.
+
+Important note: the underlying vector is an implementation detail. Even though
+this function exposes it, changes in the implementation may cause this
+function to be removed without further warning."
+ ;; KLUDGE: Without TRULY-THE the system is not smart enough to figure out that
+ ;; (1) SIMPLE-ARRAY without ARRAY-HEADER-P is a vector (2) the data vector of
+ ;; a SIMPLE-ARRAY is a vector.
+ (truly-the (simple-array * (*))
+ (if (array-header-p array)
+ (%array-data-vector array)
+ array)))