1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
|
;;; align.scm --- Alignment calculation helpers.
;; Copyright © 2018 Taylan Kammer <taylan.kammer@gmail.com>
;; This program is free software; you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.
;; This program is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
;; GNU General Public License for more details.
;; You should have received a copy of the GNU General Public License
;; along with this program. If not, see <http://www.gnu.org/licenses/>.
;;; Commentary:
;;; Code:
;;; Either remains at 'position' or rounds up to the next multiple of
;;; 'alignment' depending on whether 'size' (if not greater than 'alignment')
;;; would fit. Returns three values: the chosen position, the start of the
;;; alignment boundary of the chosen position, and the bit offset of the chosen
;;; position from the start of the alignment boundary. A bit is represented by
;;; the value 1/8.
(define (align position size alignment)
(let* ((integer (floor position))
(fraction (- position integer)))
(let-values (((prev-boundary-index offset) (floor/ integer alignment)))
(let* ((prev-boundary (* prev-boundary-index alignment))
(next-boundary (+ prev-boundary alignment)))
(if (< next-boundary (+ position (min size alignment)))
(values next-boundary next-boundary 0)
(values position prev-boundary (* 8 (+ offset fraction))))))))
;;; Returns 'position' if it's already a multiple of 'alignment'; otherwise
;;; returns the next multiple.
(define (next-boundary position alignment)
(align position +inf.0 alignment))
;;; align.scm ends here
|
