+/**
+ * base-n, 1.0
+ * Copyright (C) 2012 Andrzej Zawadzki (azawadzki@gmail.com)
+ *
+ * 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.
+**/
+#ifndef BASEN_HPP
+#define BASEN_HPP
+
+#include <algorithm>
+#include <cctype>
+#include <cassert>
+#include <cstring>
+
+namespace bn
+{
+
+template<class Iter1, class Iter2>
+void encode_b16(Iter1 start, Iter1 end, Iter2 out);
+
+template<class Iter1, class Iter2>
+void encode_b32(Iter1 start, Iter1 end, Iter2 out);
+
+template<class Iter1, class Iter2>
+void encode_b64(Iter1 start, Iter1 end, Iter2 out);
+
+template<class Iter1, class Iter2>
+void decode_b16(Iter1 start, Iter1 end, Iter2 out);
+
+template<class Iter1, class Iter2>
+void decode_b32(Iter1 start, Iter1 end, Iter2 out);
+
+template<class Iter1, class Iter2>
+void decode_b64(Iter1 start, Iter1 end, Iter2 out);
+
+namespace impl
+{
+
+const int Error = -1;
+
+namespace {
+
+char extract_partial_bits(char value, size_t start_bit, size_t bits_count)
+{
+ assert(start_bit + bits_count < 8);
+ // shift extracted bits to the beginning of the byte
+ char t1 = value >> (8 - bits_count - start_bit);
+ // mask out bits on the left
+ char t2 = t1 & ~(0xff << bits_count);
+ return t2;
+}
+
+char extract_overlapping_bits(char previous, char next, size_t start_bit, size_t bits_count)
+{
+ assert(start_bit + bits_count < 16);
+ size_t bits_count_in_previous = 8 - start_bit;
+ size_t bits_count_in_next = bits_count - bits_count_in_previous;
+ char t1 = previous << bits_count_in_next;
+ char t2 = next >> (8 - bits_count_in_next) & ~(0xff << bits_count_in_next) ;
+ return (t1 | t2) & ~(0xff << bits_count);
+}
+
+}
+
+struct b16_conversion_traits
+{
+ static size_t group_length()
+ {
+ return 4;
+ }
+
+ static char encode(unsigned int index)
+ {
+ const char* const dictionary = "0123456789ABCDEF";
+ assert(index < strlen(dictionary));
+ return dictionary[index];
+ }
+
+ static char decode(char c)
+ {
+ if (c >= '0' && c <= '9') {
+ return c - '0';
+ } else if (c >= 'A' && c <= 'F') {
+ return c - 'A' + 10;
+ }
+ return Error;
+ }
+};
+
+struct b32_conversion_traits
+{
+ static size_t group_length()
+ {
+ return 5;
+ }
+
+ static char encode(unsigned int index)
+ {
+ const char * dictionary = "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567";
+ assert(index < strlen(dictionary));
+ return dictionary[index];
+ }
+
+ static char decode(char c)
+ {
+ if (c >= 'A' && c <= 'Z') {
+ return c - 'A';
+ } else if (c >= '2' && c <= '7') {
+ return c - '2' + 26;
+ }
+ return Error;
+ }
+};
+
+struct b64_conversion_traits
+{
+ static size_t group_length()
+ {
+ return 6;
+ }
+
+ static char encode(unsigned int index)
+ {
+ const char* const dictionary = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
+ assert(index < strlen(dictionary));
+ return dictionary[index];
+ }
+
+ static char decode(char c)
+ {
+ const int alph_len = 26;
+ if (c >= 'A' && c <= 'Z') {
+ return c - 'A';
+ } else if (c >= 'a' && c <= 'z') {
+ return c - 'a' + alph_len * 1;
+ } else if (c >= '0' && c <= '9') {
+ return c - '0' + alph_len * 2;
+ } else if (c == '+') {
+ return c - '+' + alph_len * 2 + 10;
+ } else if (c == '/') {
+ return c - '/' + alph_len * 2 + 11;
+ }
+ return Error;
+ }
+};
+
+template<class ConversionTraits, class Iter1, class Iter2>
+void decode(Iter1 start, Iter1 end, Iter2 out)
+{
+ Iter1 iter = start;
+ size_t output_current_bit = 0;
+ char buffer = 0;
+
+ while (iter != end) {
+ if (std::isspace(*iter)) {
+ ++iter;
+ continue;
+ }
+ char value = ConversionTraits::decode(*iter);
+ if (value == Error) {
+ // malformed data, but let's go on...
+ ++iter;
+ continue;
+ }
+ size_t bits_in_current_byte = std::min<size_t>(output_current_bit + ConversionTraits::group_length(), 8) - output_current_bit;
+ if (bits_in_current_byte == ConversionTraits::group_length()) {
+ // the value fits within current byte, so we can extract it directly
+ buffer |= value << (8 - output_current_bit - ConversionTraits::group_length());
+ output_current_bit += ConversionTraits::group_length();
+ // check if we filled up current byte completely; in such case we flush output and continue
+ if (output_current_bit == 8) {
+ *out++ = buffer;
+ buffer = 0;
+ output_current_bit = 0;
+ }
+ } else {
+ // the value spans across the current and the next byte
+ size_t bits_in_next_byte = ConversionTraits::group_length() - bits_in_current_byte;
+ // fill the current byte and flush it to our output
+ buffer |= value >> bits_in_next_byte;
+ *out++ = buffer;
+ buffer = 0;
+ // save the remainder of our value in the buffer; it will be flushed
+ // during next iterations
+ buffer |= value << (8 - bits_in_next_byte);
+ output_current_bit = bits_in_next_byte;
+ }
+ ++iter;
+ }
+}
+
+template<class ConversionTraits, class Iter1, class Iter2>
+void encode(Iter1 start, Iter1 end, Iter2 out)
+{
+ Iter1 iter = start;
+ size_t start_bit = 0;
+ bool has_backlog = false;
+ char backlog = 0;
+
+ while (has_backlog || iter != end) {
+ if (!has_backlog) {
+ if (start_bit + ConversionTraits::group_length() < 8) {
+ // the value fits within single byte, so we can extract it
+ // directly
+ char v = extract_partial_bits(*iter, start_bit, ConversionTraits::group_length());
+ *out++ = ConversionTraits::encode(v);
+ // since we know that start_bit + ConversionTraits::group_length() < 8 we don't need to go
+ // to the next byte
+ start_bit += ConversionTraits::group_length();
+ } else {
+ // our bits are spanning across byte border; we need to keep the
+ // starting point and move over to next byte.
+ backlog = *iter++;
+ has_backlog = true;
+ }
+ } else {
+ // encode value which is made from bits spanning across byte
+ // boundary
+ char v;
+ if (iter == end)
+ v = extract_overlapping_bits(backlog, 0, start_bit, ConversionTraits::group_length());
+ else
+ v = extract_overlapping_bits(backlog, *iter, start_bit, ConversionTraits::group_length());
+ *out++ = ConversionTraits::encode(v);
+ has_backlog = false;
+ start_bit = (start_bit + ConversionTraits::group_length()) % 8;
+ }
+ }
+}
+
+} // impl
+
+using namespace bn::impl;
+
+template<class Iter1, class Iter2>
+void encode_b16(Iter1 start, Iter1 end, Iter2 out)
+{
+ encode<b16_conversion_traits>(start, end, out);
+}
+
+template<class Iter1, class Iter2>
+void encode_b32(Iter1 start, Iter1 end, Iter2 out)
+{
+ encode<b32_conversion_traits>(start, end, out);
+}
+
+template<class Iter1, class Iter2>
+void encode_b64(Iter1 start, Iter1 end, Iter2 out)
+{
+ encode<b64_conversion_traits>(start, end, out);
+}
+
+template<class Iter1, class Iter2>
+void decode_b16(Iter1 start, Iter1 end, Iter2 out)
+{
+ decode<b16_conversion_traits>(start, end, out);
+}
+
+template<class Iter1, class Iter2>
+void decode_b32(Iter1 start, Iter1 end, Iter2 out)
+{
+ decode<b32_conversion_traits>(start, end, out);
+}
+
+template<class Iter1, class Iter2>
+void decode_b64(Iter1 start, Iter1 end, Iter2 out)
+{
+ decode<b64_conversion_traits>(start, end, out);
+}
+
+} // bn
+
+#endif // BASEN_HPP