15.2.18 array-row-major-index [Function]

array-row-major-index array &rest subscripts ⇒ index

Arguments and Values::

array—an array.

subscripts—a list of valid array indices for the array.

index—a valid array row-major index for the array.

Description::

Computes the position according to the row-major ordering of array for the element that is specified by subscripts, and returns the offset of the element in the computed position from the beginning of array.

For a one-dimensional array, the result of array-row-major-index equals subscript.

array-row-major-index ignores fill pointers.

Examples::

 (setq a (make-array '(4 7) :element-type '(unsigned-byte 8)))
 (array-row-major-index a 1 2) ⇒  9
 (array-row-major-index 
    (make-array '(2 3 4) 
                :element-type '(unsigned-byte 8)
                :displaced-to a
                :displaced-index-offset 4)
    0 2 1) ⇒  9

Notes::

A possible definition of array-row-major-index, with no error-checking, is

 (defun array-row-major-index (a &rest subscripts)
   (apply #'+ (maplist #'(lambda (x y)
                            (* (car x) (apply #'* (cdr y))))
                       subscripts
                       (array-dimensions a))))