scheme48/scheme/srfi/srfi-60.scm

;; Implementation of SRFI 60 "Integers as Bits" for Scheme 48, based on
;; reference implementation.

;; Copyright (C) Aubrey Jaffer (2004, 2005). 
;; Copyright (C) 2005 David Van Horn
;; All Rights Reserved.
;; 
;; Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: 
;; 
;; The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. 
;; 
;; THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

;; Released under the same terms as the SRFI reference implementation
;; included below.


;; SRFI 60 defines several procedures which are already provided
;; by Scheme48's bitwise structure, namely bit-count,
;; bitwise-{ior,xor,and,not}, and arithmetic-shift, which are used
;; for the implementation of this library, and exported by this
;; structure.

(define logior bitwise-ior)
(define logxor bitwise-xor)
(define logand bitwise-and)
(define lognot bitwise-not)  
(define logcount bit-count)

;; The reference implementation follows below and has been changed only
;; by adding S-expression comments to definitions which are not needed,
;; such as definitions implemented as Scheme 48 exact integer primitives.

;;;; "logical.scm", bit access and operations for integers for Scheme
;;; Copyright (C) 1991, 1993, 2001, 2003, 2005 Aubrey Jaffer
;
;Permission to copy this software, to modify it, to redistribute it,
;to distribute modified versions, and to use it for any purpose is
;granted, subject to the following restrictions and understandings.
;
;1.  Any copy made of this software must include this copyright notice
;in full.
;
;2.  I have made no warranty or representation that the operation of
;this software will be error-free, and I am under no obligation to
;provide any services, by way of maintenance, update, or otherwise.
;
;3.  In conjunction with products arising from the use of this
;material, there shall be no use of my name in any advertising,
;promotional, or sales literature without prior written consent in
;each case.

; (define logical:boole-xor
;  '#(#(0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15)
;     #(1 0 3 2 5 4 7 6 9 8 11 10 13 12 15 14)
;     #(2 3 0 1 6 7 4 5 10 11 8 9 14 15 12 13)
;     #(3 2 1 0 7 6 5 4 11 10 9 8 15 14 13 12)
;     #(4 5 6 7 0 1 2 3 12 13 14 15 8 9 10 11)
;     #(5 4 7 6 1 0 3 2 13 12 15 14 9 8 11 10)
;     #(6 7 4 5 2 3 0 1 14 15 12 13 10 11 8 9)
;     #(7 6 5 4 3 2 1 0 15 14 13 12 11 10 9 8)
;     #(8 9 10 11 12 13 14 15 0 1 2 3 4 5 6 7)
;     #(9 8 11 10 13 12 15 14 1 0 3 2 5 4 7 6)
;     #(10 11 8 9 14 15 12 13 2 3 0 1 6 7 4 5)
;     #(11 10 9 8 15 14 13 12 3 2 1 0 7 6 5 4)
;     #(12 13 14 15 8 9 10 11 4 5 6 7 0 1 2 3)
;     #(13 12 15 14 9 8 11 10 5 4 7 6 1 0 3 2)
;     #(14 15 12 13 10 11 8 9 6 7 4 5 2 3 0 1)
;     #(15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0)))
; 
; (define logical:boole-and
;  '#(#(0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0)
;     #(0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1)
;     #(0 0 2 2 0 0 2 2 0 0 2 2 0 0 2 2)
;     #(0 1 2 3 0 1 2 3 0 1 2 3 0 1 2 3)
;     #(0 0 0 0 4 4 4 4 0 0 0 0 4 4 4 4)
;     #(0 1 0 1 4 5 4 5 0 1 0 1 4 5 4 5)
;     #(0 0 2 2 4 4 6 6 0 0 2 2 4 4 6 6)
;     #(0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7)
;     #(0 0 0 0 0 0 0 0 8 8 8 8 8 8 8 8)
;     #(0 1 0 1 0 1 0 1 8 9 8 9 8 9 8 9)
;     #(0 0 2 2 0 0 2 2 8 8 10 10 8 8 10 10)
;     #(0 1 2 3 0 1 2 3 8 9 10 11 8 9 10 11)
;     #(0 0 0 0 4 4 4 4 8 8 8 8 12 12 12 12)
;     #(0 1 0 1 4 5 4 5 8 9 8 9 12 13 12 13)
;     #(0 0 2 2 4 4 6 6 8 8 10 10 12 12 14 14)
;     #(0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15)))

(define (logical:ash-4 x)
  (if (negative? x)
      (+ -1 (quotient (+ 1 x) 16))
      (quotient x 16)))

; (define (logical:reduce op4 ident)
;   (lambda args
;     (do ((res ident (op4 res (car rgs) 1 0))
; 	 (rgs args (cdr rgs)))
; 	((null? rgs) res))))

;
; (define logand
;   (letrec
;       ((lgand
; 	(lambda (n2 n1 scl acc)
; 	  (cond ((= n1 n2) (+ acc (* scl n1)))
; 		((zero? n2) acc)
; 		((zero? n1) acc)
; 		(else (lgand (logical:ash-4 n2)
; 			     (logical:ash-4 n1)
; 			     (* 16 scl)
; 			     (+ (* (vector-ref (vector-ref logical:boole-and
; 							   (modulo n1 16))
; 					       (modulo n2 16))
; 				   scl)
; 				acc)))))))
;     (logical:reduce lgand -1)))
;
; (define logior
;   (letrec
;       ((lgior
; 	(lambda (n2 n1 scl acc)
; 	  (cond ((= n1 n2) (+ acc (* scl n1)))
; 		((zero? n2) (+ acc (* scl n1)))
; 		((zero? n1) (+ acc (* scl n2)))
; 		(else (lgior (logical:ash-4 n2)
; 			     (logical:ash-4 n1)
; 			     (* 16 scl)
; 			     (+ (* (- 15 (vector-ref
; 					  (vector-ref logical:boole-and
; 						      (- 15 (modulo n1 16)))
; 					  (- 15 (modulo n2 16))))
; 				   scl)
; 				acc)))))))
;     (logical:reduce lgior 0)))
;
; (define logxor
;   (letrec
;       ((lgxor
; 	(lambda (n2 n1 scl acc)
; 	  (cond ((= n1 n2) acc)
; 		((zero? n2) (+ acc (* scl n1)))
; 		((zero? n1) (+ acc (* scl n2)))
; 		(else (lgxor (logical:ash-4 n2)
; 			     (logical:ash-4 n1)
; 			     (* 16 scl)
; 			     (+ (* (vector-ref (vector-ref logical:boole-xor
; 							   (modulo n1 16))
; 					       (modulo n2 16))
; 				   scl)
; 				acc)))))))
;     (logical:reduce lgxor 0)))
;
; (define (lognot n) (- -1 n))

(define (logtest n1 n2)
  (not (zero? (logand n1 n2))))

(define (logbit? index n)
  (logtest (expt 2 index) n))

(define (copy-bit index to bool)
  (if bool
      (logior to (arithmetic-shift 1 index))
      (logand to (lognot (arithmetic-shift 1 index)))))

(define (bitwise-if mask n0 n1)
  (logior (logand mask n0)
	  (logand (lognot mask) n1)))

(define (bit-field n start end)
  (logand (lognot (ash -1 (- end start)))
	  (arithmetic-shift n (- start))))

(define (copy-bit-field to from start end)
  (bitwise-if (arithmetic-shift (lognot (ash -1 (- end start))) start)
	      (arithmetic-shift from start)
	      to))

(define (rotate-bit-field n count start end)
  (define width (- end start))
  (set! count (modulo count width))
  (let ((mask (lognot (ash -1 width))))
    (define zn (logand mask (arithmetic-shift n (- start))))
    (logior (arithmetic-shift
	     (logior (logand mask (arithmetic-shift zn count))
		     (arithmetic-shift zn (- count width)))
	     start)
	    (logand (lognot (ash mask start)) n))))

; (define (arithmetic-shift n count)
;   (if (negative? count)
;       (let ((k (expt 2 (- count))))
; 	(if (negative? n)
; 	    (+ -1 (quotient (+ 1 n) k))
; 	    (quotient n k)))
;       (* (expt 2 count) n)))

(define integer-length
  (letrec ((intlen (lambda (n tot)
		     (case n
		       ((0 -1) (+ 0 tot))
		       ((1 -2) (+ 1 tot))
		       ((2 3 -3 -4) (+ 2 tot))
		       ((4 5 6 7 -5 -6 -7 -8) (+ 3 tot))
		       (else (intlen (logical:ash-4 n) (+ 4 tot)))))))
    (lambda (n) (intlen n 0))))

; (define logcount
;   (letrec ((logcnt (lambda (n tot)
; 		     (if (zero? n)
; 			 tot
; 			 (logcnt (quotient n 16)
; 				 (+ (vector-ref
; 				     '#(0 1 1 2 1 2 2 3 1 2 2 3 2 3 3 4)
; 				     (modulo n 16))
; 				    tot))))))
;     (lambda (n)
;       (cond ((negative? n) (logcnt (lognot n) 0))
; 	    ((positive? n) (logcnt n 0))
; 	    (else 0)))))

(define (log2-binary-factors n)
  (+ -1 (integer-length (logand n (- n)))))

(define (bit-reverse k n)
  (do ((m (if (negative? n) (lognot n) n) (arithmetic-shift m -1))
       (k (+ -1 k) (+ -1 k))
       (rvs 0 (logior (arithmetic-shift rvs 1) (logand 1 m))))
      ((negative? k) (if (negative? n) (lognot rvs) rvs))))

(define (reverse-bit-field n start end)
  (define width (- end start))
  (let ((mask (lognot (ash -1 width))))
    (define zn (logand mask (arithmetic-shift n (- start))))
    (logior (arithmetic-shift (bit-reverse width zn) start)
	    (logand (lognot (ash mask start)) n))))

(define (integer->list k . len)
  (if (null? len)
      (do ((k k (arithmetic-shift k -1))
	   (lst '() (cons (odd? k) lst)))
	  ((<= k 0) lst))
      (do ((idx (+ -1 (car len)) (+ -1 idx))
	   (k k (arithmetic-shift k -1))
	   (lst '() (cons (odd? k) lst)))
	  ((negative? idx) lst))))

(define (list->integer bools)
  (do ((bs bools (cdr bs))
       (acc 0 (+ acc acc (if (car bs) 1 0))))
      ((null? bs) acc)))
(define (booleans->integer . bools)
  (list->integer bools))

;;;; SRFI-60 aliases
(define ash arithmetic-shift)
; (define bitwise-ior logior)
; (define bitwise-xor logxor)
; (define bitwise-and logand)
; (define bitwise-not lognot)
; (define bit-count logcount)
(define bit-set?   logbit?)
(define any-bits-set? logtest)
(define first-set-bit log2-binary-factors)
(define bitwise-merge bitwise-if)

;;; Legacy
;;(define (logical:rotate k count len) (rotate-bit-field k count 0 len))
;;(define (logical:ones deg) (lognot (ash -1 deg)))
;;(define integer-expt expt)		; legacy name