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;;; GNU Guix --- Functional package management for GNU
;;; Copyright © 2012, 2014, 2017 Ludovic Courtès <ludo@gnu.org>
;;; Copyright © 2021 Maxime Devos <maximedevos@telenet.be>
;;;
;;; 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))
(define utf8 (make-bytevector (* len 2)))
(let-syntax ((base16-octet-pairs
(lambda (s)
(syntax-case s ()
(_
(string->utf8
(string-concatenate
(unfold (cut > <> 255)
(lambda (n)
(format #f "~2,'0x" n))
1+
0))))))))
(define octet-pairs base16-octet-pairs)
(let loop ((i 0))
(when (< i len)
(bytevector-u16-native-set!
utf8 (* 2 i)
(bytevector-u16-native-ref octet-pairs
(* 2 (bytevector-u8-ref bv i))))
(loop (+ i 1))))
(utf8->string utf8)))
(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)))
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