array-row-major-index (Function)

Syntax:

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))))