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;;; GNU Guix --- Functional package management for GNU
;;; Copyright © 2012 Ludovic Courtès <ludo@gnu.org>
;;;
;;; This file is part of GNU Guix.
;;;
;;; GNU Guix 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.
;;;
;;; GNU Guix 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 GNU Guix. If not, see <http://www.gnu.org/licenses/>.
(define-module (guix base32)
#:use-module (srfi srfi-1)
#:use-module (srfi srfi-60)
#:use-module (rnrs bytevectors)
#:use-module (ice-9 vlist)
#:export (bytevector-quintet-length
bytevector->base32-string
bytevector->nix-base32-string
base32-string->bytevector
nix-base32-string->bytevector))
;;; Commentary:
;;;
;;; A generic, customizable to convert bytevectors to/from a base32
;;; representation.
;;;
;;; Code:
(define bytevector-quintet-ref
(let* ((ref bytevector-u8-ref)
(ref+ (lambda (bv offset)
(let ((o (+ 1 offset)))
(if (>= o (bytevector-length bv))
0
(bytevector-u8-ref bv o)))))
(ref0 (lambda (bv offset)
(bit-field (ref bv offset) 3 8)))
(ref1 (lambda (bv offset)
(logior (ash (bit-field (ref bv offset) 0 3) 2)
(bit-field (ref+ bv offset) 6 8))))
(ref2 (lambda (bv offset)
(bit-field (ref bv offset) 1 6)))
(ref3 (lambda (bv offset)
(logior (ash (bit-field (ref bv offset) 0 1) 4)
(bit-field (ref+ bv offset) 4 8))))
(ref4 (lambda (bv offset)
(logior (ash (bit-field (ref bv offset) 0 4) 1)
(bit-field (ref+ bv offset) 7 8))))
(ref5 (lambda (bv offset)
(bit-field (ref bv offset) 2 7)))
(ref6 (lambda (bv offset)
(logior (ash (bit-field (ref bv offset) 0 2) 3)
(bit-field (ref+ bv offset) 5 8))))
(ref7 (lambda (bv offset)
(bit-field (ref bv offset) 0 5)))
(refs (vector ref0 ref1 ref2 ref3 ref4 ref5 ref6 ref7)))
(lambda (bv index)
"Return the INDEXth quintet of BV."
(let ((p (vector-ref refs (modulo index 8))))
(p bv (quotient (* index 5) 8))))))
(define bytevector-quintet-ref-right
(let* ((ref bytevector-u8-ref)
(ref+ (lambda (bv offset)
(let ((o (+ 1 offset)))
(if (>= o (bytevector-length bv))
0
(bytevector-u8-ref bv o)))))
(ref0 (lambda (bv offset)
(bit-field (ref bv offset) 0 5)))
(ref1 (lambda (bv offset)
(logior (bit-field (ref bv offset) 5 8)
(ash (bit-field (ref+ bv offset) 0 2) 3))))
(ref2 (lambda (bv offset)
(bit-field (ref bv offset) 2 7)))
(ref3 (lambda (bv offset)
(logior (bit-field (ref bv offset) 7 8)
(ash (bit-field (ref+ bv offset) 0 4) 1))))
(ref4 (lambda (bv offset)
(logior (bit-field (ref bv offset) 4 8)
(ash (bit-field (ref+ bv offset) 0 1) 4))))
(ref5 (lambda (bv offset)
(bit-field (ref bv offset) 1 6)))
(ref6 (lambda (bv offset)
(logior (bit-field (ref bv offset) 6 8)
(ash (bit-field (ref+ bv offset) 0 3) 2))))
(ref7 (lambda (bv offset)
(bit-field (ref bv offset) 3 8)))
(refs (vector ref0 ref1 ref2 ref3 ref4 ref5 ref6 ref7)))
(lambda (bv index)
"Return the INDEXth quintet of BV, assuming quintets start from the
least-significant bits, contrary to what RFC 4648 describes."
(let ((p (vector-ref refs (modulo index 8))))
(p bv (quotient (* index 5) 8))))))
(define (bytevector-quintet-length bv)
"Return the number of quintets (including truncated ones) available in BV."
(ceiling (/ (* (bytevector-length bv) 8) 5)))
(define (bytevector-quintet-fold proc init bv)
"Return the result of applying PROC to each quintet of BV and the result of
the previous application or INIT."
(define len
(bytevector-quintet-length bv))
(let loop ((i 0)
(r init))
(if (= i len)
r
(loop (1+ i) (proc (bytevector-quintet-ref bv i) r)))))
(define (bytevector-quintet-fold-right proc init bv)
"Return the result of applying PROC to each quintet of BV and the result of
the previous application or INIT."
(define len
(bytevector-quintet-length bv))
(let loop ((i len)
(r init))
(if (zero? i)
r
(let ((j (- i 1)))
(loop j (proc (bytevector-quintet-ref-right bv j) r))))))
(define (make-bytevector->base32-string quintet-fold base32-chars)
(lambda (bv)
"Return a base32 encoding of BV using BASE32-CHARS as the alphabet."
(let ((chars (quintet-fold (lambda (q r)
(cons (vector-ref base32-chars q)
r))
'()
bv)))
(list->string (reverse chars)))))
(define %nix-base32-chars
;; See `libutil/hash.cc'.
#(#\0 #\1 #\2 #\3 #\4 #\5 #\6 #\7 #\8 #\9
#\a #\b #\c #\d #\f #\g #\h #\i #\j #\k #\l #\m #\n
#\p #\q #\r #\s #\v #\w #\x #\y #\z))
(define %rfc4648-base32-chars
#(#\a #\b #\c #\d #\e #\f #\g #\h #\i #\j #\k #\l #\m
#\n #\o #\p #\q #\r #\s #\t #\u #\v #\w #\x #\y #\z
#\2 #\3 #\4 #\5 #\6 #\7))
(define bytevector->base32-string
(make-bytevector->base32-string bytevector-quintet-fold
%rfc4648-base32-chars))
(define bytevector->nix-base32-string
(make-bytevector->base32-string bytevector-quintet-fold-right
%nix-base32-chars))
(define bytevector-quintet-set!
(let* ((setq! (lambda (bv offset start stop value)
(let ((v (bytevector-u8-ref bv offset))
(w (arithmetic-shift value start))
(m (bitwise-xor (1- (expt 2 stop))
(1- (expt 2 start)))))
(bytevector-u8-set! bv offset
(bitwise-merge m w v)))))
(set0! (lambda (bv offset value)
(setq! bv offset 3 8 value)))
(set1! (lambda (bv offset value)
(setq! bv offset 0 3 (bit-field value 2 5))
(or (= (+ 1 offset) (bytevector-length bv))
(setq! bv (+ 1 offset) 6 8 (bit-field value 0 2)))))
(set2! (lambda (bv offset value)
(setq! bv offset 1 6 value)))
(set3! (lambda (bv offset value)
(setq! bv offset 0 1 (bit-field value 4 5))
(or (= (+ 1 offset) (bytevector-length bv))
(setq! bv (+ 1 offset) 4 8 (bit-field value 0 4)))))
(set4! (lambda (bv offset value)
(setq! bv offset 0 4 (bit-field value 1 5))
(or (= (+ 1 offset) (bytevector-length bv))
(setq! bv (+ 1 offset) 7 8 (bit-field value 0 1)))))
(set5! (lambda (bv offset value)
(setq! bv offset 2 7 value)))
(set6! (lambda (bv offset value)
(setq! bv offset 0 2 (bit-field value 3 5))
(or (= (+ 1 offset) (bytevector-length bv))
(setq! bv (+ 1 offset) 5 8 (bit-field value 0 3)))))
(set7! (lambda (bv offset value)
(setq! bv offset 0 5 value)))
(sets (vector set0! set1! set2! set3! set4! set5! set6! set7!)))
(lambda (bv index value)
"Set the INDEXth quintet of BV to VALUE."
(let ((p (vector-ref sets (modulo index 8))))
(p bv (quotient (* index 5) 8) (logand value #x1f))))))
(define bytevector-quintet-set-right!
(let* ((setq! (lambda (bv offset start stop value)
(let ((v (bytevector-u8-ref bv offset))
(w (arithmetic-shift value start))
(m (bitwise-xor (1- (expt 2 stop))
(1- (expt 2 start)))))
(bytevector-u8-set! bv offset
(bitwise-merge m w v)))))
(set0! (lambda (bv offset value)
(setq! bv offset 0 5 value)))
(set1! (lambda (bv offset value)
(setq! bv offset 5 8 (bit-field value 0 3))
(or (= (+ 1 offset) (bytevector-length bv))
(setq! bv (+ 1 offset) 0 2 (bit-field value 3 5)))))
(set2! (lambda (bv offset value)
(setq! bv offset 2 7 value)))
(set3! (lambda (bv offset value)
(setq! bv offset 7 8 (bit-field value 0 1))
(or (= (+ 1 offset) (bytevector-length bv))
(setq! bv (+ 1 offset) 0 4 (bit-field value 1 5)))))
(set4! (lambda (bv offset value)
(setq! bv offset 4 8 (bit-field value 0 4))
(or (= (+ 1 offset) (bytevector-length bv))
(setq! bv (+ 1 offset) 0 1 (bit-field value 4 5)))))
(set5! (lambda (bv offset value)
(setq! bv offset 1 6 value)))
(set6! (lambda (bv offset value)
(setq! bv offset 6 8 (bit-field value 0 2))
(or (= (+ 1 offset) (bytevector-length bv))
(setq! bv (+ 1 offset) 0 3 (bit-field value 2 5)))))
(set7! (lambda (bv offset value)
(setq! bv offset 3 8 value)))
(sets (vector set0! set1! set2! set3! set4! set5! set6! set7!)))
(lambda (bv index value)
"Set the INDEXth quintet of BV to VALUE, assuming quintets start from
the least-significant bits."
(let ((p (vector-ref sets (modulo index 8))))
(p bv (quotient (* index 5) 8) (logand value #x1f))))))
(define (base32-string-unfold f s)
"Given procedure F which, when applied to a character, returns the
corresponding quintet, return the bytevector corresponding to string S."
(define len (string-length s))
(let ((bv (make-bytevector (quotient (* len 5) 8))))
(string-fold (lambda (chr index)
(bytevector-quintet-set! bv index (f chr))
(+ 1 index))
0
s)
bv))
(define (base32-string-unfold-right f s)
"Given procedure F which, when applied to a character, returns the
corresponding quintet, return the bytevector corresponding to string S,
starting from the right of S."
(define len (string-length s))
(let ((bv (make-bytevector (quotient (* len 5) 8))))
(string-fold-right (lambda (chr index)
(bytevector-quintet-set-right! bv index (f chr))
(+ 1 index))
0
s)
bv))
(define (make-base32-string->bytevector base32-string-unfold base32-chars)
(let ((char->value (let loop ((i 0)
(v vlist-null))
(if (= i (vector-length base32-chars))
v
(loop (+ 1 i)
(vhash-consv (vector-ref base32-chars i)
i v))))))
(lambda (s)
"Return the binary representation of base32 string S as a bytevector."
(base32-string-unfold (lambda (chr)
(or (and=> (vhash-assv chr char->value) cdr)
(error "invalid base32 character" chr)))
s))))
(define base32-string->bytevector
(make-base32-string->bytevector base32-string-unfold %rfc4648-base32-chars))
(define nix-base32-string->bytevector
(make-base32-string->bytevector base32-string-unfold-right %nix-base32-chars))
;;; base32.scm ends here
|
