array-row-major-index (original) (raw)

ANSI Common Lisp 15 Arrays 15.2 Dictionary of Arrays

Syntax:

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-indexequals 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))))

Allegro CL Implementation Details:

None.