;;; GNU Guix --- Functional package management for GNU ;;; Copyright © 2012, 2014, 2017 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 base16) #:use-module (srfi srfi-1) #:use-module (srfi srfi-26) #:use-module (srfi srfi-60) #:use-module (rnrs bytevectors) #:use-module (ice-9 vlist) #:use-module (ice-9 format) #:export (bytevector->base16-string base16-string->bytevector)) ;;; ;;; Base 16. ;;; (define (bytevector->base16-string bv) "Return the hexadecimal representation of BV's contents." (define len (bytevector-length bv)) (let-syntax ((base16-chars (lambda (s) (syntax-case s () (_ (let ((v (list->vector (unfold (cut > <> 255) (lambda (n) (format #f "~2,'0x" n)) 1+ 0)))) v)))))) (define chars base16-chars) (let loop ((i len) (r '())) (if (zero? i) (string-concatenate r) (let ((i (- i 1))) (loop i (cons (vector-ref chars (bytevector-u8-ref bv i)) r))))))) (define base16-string->bytevector (let ((chars->value (fold (lambda (i r) (vhash-consv (string-ref (number->string i 16) 0) i r)) vlist-null (iota 16)))) (lambda (s) "Return the bytevector whose hexadecimal representation is string S." (define bv (make-bytevector (quotient (string-length s) 2) 0)) (string-fold (lambda (chr i) (let ((j (quotient i 2)) (v (and=> (vhash-assv chr chars->value) cdr))) (if v (if (zero? (logand i 1)) (bytevector-u8-set! bv j (arithmetic-shift v 4)) (let ((w (bytevector-u8-ref bv j))) (bytevector-u8-set! bv j (logior v w)))) (error "invalid hexadecimal character" chr))) (+ i 1)) 0 s) bv)))