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-rw-r--r--makcrc.scm49
1 files changed, 29 insertions, 20 deletions
diff --git a/makcrc.scm b/makcrc.scm
index 3ea80d5..debd5c9 100644
--- a/makcrc.scm
+++ b/makcrc.scm
@@ -1,9 +1,9 @@
;;;; "makcrc.scm" Compute Cyclic Checksums
-;;; Copyright (C) 1995, 1996, 1997 Aubrey Jaffer.
+;;; Copyright (C) 1995, 1996, 1997, 2001 Aubrey Jaffer
;
-;Permission to copy this software, to redistribute it, and to use it
-;for any purpose is granted, subject to the following restrictions and
-;understandings.
+;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.
@@ -17,27 +17,39 @@
;promotional, or sales literature without prior written consent in
;each case.
+(require 'byte)
(require 'logical)
-;;;(define crc (eval (make-port-crc 16 #o010013)))
-;;;(define crc (eval (make-port-crc 08 #o053)))
-;;;(define (file-check-sum file) (call-with-input-file file crc32))
-
(define (make-port-crc . margs)
(define (make-mask hibit)
(+ (ash (+ -1 (ash 1 (+ 1 (- hibit 2)))) 1) 1))
- (define accum-bits 32)
(define chunk-bits (integer-length (+ -1 char-code-limit)))
+ (define accum-bits #f)
(define generator #f)
- (cond ((pair? margs)
- (set! accum-bits (car margs))
- (cond ((pair? (cdr margs))
- (set! generator (cadr margs))))))
+ (case (length margs)
+ ((0) #t)
+ ((1) (if (< (car margs) 128)
+ (set! accum-bits (car margs))
+ (set! generator (car margs))))
+ ((2)
+ (set! accum-bits (car margs))
+ (set! generator (cadr margs)))
+ (else (slib:error 'make-port-crc 'args margs)))
(cond ((not generator)
(case accum-bits
- ((32) (set! generator #b00000100110000010001110110110111))
+ ((#f 32) (set! accum-bits 32)
+ (set! generator #b00000100110000010001110110110111)) ; CRC-32
+ ((16) (set! generator #b0001000000001011)) ; CRC-16
+ ;;((16) (set! generator #b0001000000100001)) ; CRC-CCIT
+ ;;((08) (set! generator #b101011))
(else (slib:error 'make-port-crc "no default polynomial for"
- accum-bits "bits")))))
+ accum-bits "bits"))))
+ ((not accum-bits)
+ (set! accum-bits (+ -1 (integer-length generator)))))
+ (set! generator (logand generator (lognot (ash 1 accum-bits))))
+ (cond ((>= (integer-length generator) accum-bits)
+ (slib:error 'make-port-crc
+ "generator longer than" accum-bits "bits")))
(let* ((chunk-mask (make-mask chunk-bits))
(crctab (make-vector (+ 1 chunk-mask))))
(define (accum src)
@@ -69,17 +81,14 @@
(do ((i 0 (+ 1 i)))
((> i chunk-mask))
(vector-set! crctab i (remd i)))))
- (cond ((>= (integer-length generator) accum-bits)
- (slib:error 'make-port-crc
- "generator longer than" accum-bits "bits")))
(make-crc-table)
`(lambda (port)
(define crc 0)
(define byte-count 0)
(define crctab ',crctab)
- (do ((ci (read-char port) (read-char port)))
+ (do ((ci (read-byte port) (read-byte port)))
((eof-object? ci))
- ,(accum '(char->integer ci))
+ ,(accum 'ci)
(set! byte-count (+ 1 byte-count)))
(do ((byte-count byte-count (ash byte-count ,(- chunk-bits))))
((zero? byte-count))