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    /* base16.h
     *
     * Hex encoding and decoding, following spki conventions (i.e.
     * allowing whitespace between digits).
     */
    
    /* nettle, low-level cryptographics library
     *
     * Copyright (C) 2002 Niels Mller
     *  
     * The nettle library is free software; you can redistribute it and/or modify
     * it under the terms of the GNU Lesser General Public License as published by
     * the Free Software Foundation; either version 2.1 of the License, or (at your
     * option) any later version.
     * 
     * The nettle library 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 Lesser General Public
     * License for more details.
     * 
     * You should have received a copy of the GNU Lesser General Public License
     * along with the nettle library; see the file COPYING.LIB.  If not, write to
     * the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
     * MA 02111-1307, USA.
     */
     
    #ifndef NETTLE_BASE16_H_INCLUDED
    #define NETTLE_BASE16_H_INCLUDED
    
    
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    /* Name mangling */
    #define base16_encode_single nettle_base16_encode_single
    #define base16_encode_update nettle_base16_encode_update
    #define base16_decode_init nettle_base16_decode_init
    #define base16_decode_single nettle_base16_decode_single
    #define base16_decode_update nettle_base16_decode_update
    #define base16_decode_final nettle_base16_decode_final
    
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    /* Base16 encoding */
    
    /* Maximum length of output for base16_encode_update. */
    #define BASE16_ENCODE_LENGTH(length) ((length) * 2)
    
    /* Encodes a single byte. Always stores two digits in dst[0] and dst[1]. */
    void
    base16_encode_single(uint8_t *dst,
    		     uint8_t src);
    
    /* Always stores BASE16_ENCODE_LENGTH(length) digits in dst. */
    void
    base16_encode_update(uint8_t *dst,
    		     unsigned length,
    		     const uint8_t *src);
    
    
    /* Base16 decoding */
    
    /* Maximum length of output for base16_decode_update. */
    /* We have at most 4 buffered bits, and a total of (length + 1) * 4 bits. */
    #define BASE16_DECODE_LENGTH(length) (((length) + 1) / 2)
    
    struct base16_decode_ctx
    {
      unsigned word;   /* Leftover bits */
      unsigned bits;   /* Number buffered bits */
    };
    
    void
    base16_decode_init(struct base16_decode_ctx *ctx);
    
    /* Decodes a single byte. Returns amount of output (0 or 1), or -1 on
     * errors. */
    int
    base16_decode_single(struct base16_decode_ctx *ctx,
    		     uint8_t *dst,
    		     uint8_t src);
    
    /* Returns 1 on success, 0 on error. DST should point to an area of
     * size at least BASE16_DECODE_LENGTH(length), and for sanity
     * checking, *DST_LENGTH should be initialized to the size of that
     * area before the call. *DST_LENGTH is updated to the amount of
     * decoded output. */
    
    /* FIXME: Currently results in an assertion failure if *DST_LENGTH is
     * too small. Return some error instead? */
    int
    base16_decode_update(struct base16_decode_ctx *ctx,
    		     unsigned *dst_length,
    		     uint8_t *dst,
    		     unsigned src_length,
    		     const uint8_t *src);
    
    /* Returns 1 on success. */
    int
    base16_decode_final(struct base16_decode_ctx *ctx);
    
    #endif /* NETTLE_BASE16_H_INCLUDED */