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;;; guile-gcrypt --- crypto tooling for guile
;;; Copyright © 2012, 2014, 2017 Ludovic Courtès <ludo@gnu.org>
;;;
;;; This file is part of guile-gcrypt.
;;;
;;; guile-gcrypt 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.
;;;
;;; guile-gcrypt 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 guile-gcrypt. If not, see <http://www.gnu.org/licenses/>.
(define-module (gcrypt 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)))
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