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;;; Guix --- Nix package management from Guile. -*- coding: utf-8 -*-
;;; Copyright (C) 2012 Ludovic Courtès <ludo@gnu.org>
;;;
;;; This file is part of Guix.
;;;
;;; 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.
;;;
;;; 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 Guix. If not, see <http://www.gnu.org/licenses/>.
(define-module (guix utils)
#:use-module (srfi srfi-60)
#:use-module (rnrs bytevectors)
#:export (bytevector-quintet-length
bytevector->base32-string
bytevector->nix-base32-string))
(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-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 (make-bytevector->base32-string base32-chars)
(lambda (bv)
"Return a base32 encoding of BV using BASE32-CHARS as the alphabet."
(let ((chars (bytevector-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 %rfc4648-base32-chars))
(define bytevector->nix-base32-string
(make-bytevector->base32-string %nix-base32-chars))
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