Next: , Previous: array-rank, Up: Arrays Dictionary


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))))