base32.cpp

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/* Copyright (c) 2010 Wildfire Games
 *
 * Permission is hereby granted, free of charge, to any person obtaining
 * a copy of this software and associated documentation files (the
 * "Software"), to deal in the Software without restriction, including
 * without limitation the rights to use, copy, modify, merge, publish,
 * distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
 * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
 * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
 * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
 * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */

/*
 * base32 conversion
 */

#include "precompiled.h"


// big endian!
void base32(const size_t in_len, const u8* in, u8* out)
{
    u32 pool = 0;   // of bits from buffer
    ssize_t pool_bits = 0;  // # bits currently in buffer

    static const u8 tbl[33] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567";

    size_t in_bytes_left = in_len;  // to avoid overrunning input buffer
    const size_t out_chars = (in_len*8 + 4) / 5;    // = ceil(# 5-bit blocks)
    for(size_t i = 0; i < out_chars; i++)
    {
        if(pool_bits < 5 && in_bytes_left)
        {
            pool <<= 8;
            pool |= *in++;
            pool_bits += 8;
            in_bytes_left--;
        }

        pool_bits -= 5;
        size_t c;
        if (pool_bits < 0)
            c = (pool << -pool_bits) & 31;
        else
            c = (pool >> pool_bits) & 31;
        *out++ = tbl[c];
    }

    *out++ = '\0';
}