1 files changed, 221 insertions, 0 deletions
diff --git a/movement/lib/base32/base32.c b/movement/lib/base32/base32.c
new file mode 100644
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+++ b/movement/lib/base32/base32.c
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+/**
+ * base32 (de)coder implementation as specified by RFC4648.
+ *
+ * Copyright (c) 2010 Adrien Kunysz
+ *
+ * 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.
+ **/
+
+#include <assert.h>  // assert()
+#include <limits.h>  // CHAR_BIT
+
+#include "base32.h"
+
+/**
+ * Let this be a sequence of plain data before encoding:
+ *
+ *  01234567 01234567 01234567 01234567 01234567
+ * +--------+--------+--------+--------+--------+
+ * |< 0 >< 1| >< 2 ><|.3 >< 4.|>< 5 ><.|6 >< 7 >|
+ * +--------+--------+--------+--------+--------+
+ *
+ * There are 5 octets of 8 bits each in each sequence.
+ * There are 8 blocks of 5 bits each in each sequence.
+ *
+ * You probably want to refer to that graph when reading the algorithms in this
+ * file. We use "octet" instead of "byte" intentionnaly as we really work with
+ * 8 bits quantities. This implementation will probably not work properly on
+ * systems that don't have exactly 8 bits per (unsigned) char.
+ **/
+
+static size_t min(size_t x, size_t y)
+{
+	return x < y ? x : y;
+}
+
+static const unsigned char PADDING_CHAR = '=';
+
+/**
+ * Pad the given buffer with len padding characters.
+ */
+static void pad(unsigned char *buf, int len)
+{
+	for (int i = 0; i < len; i++)
+		buf[i] = PADDING_CHAR;
+}
+
+/**
+ * This convert a 5 bits value into a base32 character.
+ * Only the 5 least significant bits are used.
+ */
+static unsigned char encode_char(unsigned char c)
+{
+	static unsigned char base32[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567";
+	return base32[c & 0x1F];  // 0001 1111
+}
+
+/**
+ * Decode given character into a 5 bits value. 
+ * Returns -1 iff the argument given was an invalid base32 character
+ * or a padding character.
+ */
+static int decode_char(unsigned char c)
+{
+	char retval = -1;
+
+	if (c >= 'A' && c <= 'Z')
+		retval = c - 'A';
+	if (c >= '2' && c <= '7')
+		retval = c - '2' + 26;
+
+	assert(retval == -1 || ((retval & 0x1F) == retval));
+
+	return  retval;
+}
+
+/**
+ * Given a block id between 0 and 7 inclusive, this will return the index of
+ * the octet in which this block starts. For example, given 3 it will return 1
+ * because block 3 starts in octet 1:
+ *
+ * +--------+--------+
+ * | ......<|.3 >....|
+ * +--------+--------+
+ *  octet 1 | octet 2
+ */
+static int get_octet(int block)
+{
+	assert(block >= 0 && block < 8);
+	return (block*5) / 8;
+}
+
+/**
+ * Given a block id between 0 and 7 inclusive, this will return how many bits
+ * we can drop at the end of the octet in which this block starts. 
+ * For example, given block 0 it will return 3 because there are 3 bits
+ * we don't care about at the end:
+ *
+ *  +--------+-
+ *  |< 0 >...|
+ *  +--------+-
+ *
+ * Given block 1, it will return -2 because there
+ * are actually two bits missing to have a complete block:
+ *
+ *  +--------+-
+ *  |.....< 1|..
+ *  +--------+-
+ **/
+static int get_offset(int block)
+{
+	assert(block >= 0 && block < 8);
+	return (8 - 5 - (5*block) % 8);
+}
+
+/**
+ * Like "b >> offset" but it will do the right thing with negative offset.
+ * We need this as bitwise shifting by a negative offset is undefined
+ * behavior.
+ */
+static unsigned char shift_right(unsigned char byte, char offset)
+{
+	if (offset > 0)
+		return byte >>  offset;
+	else
+		return byte << -offset;
+}
+
+static unsigned char shift_left(unsigned char byte, char offset)
+{
+	return shift_right(byte, - offset);
+}
+
+/**
+ * Encode a sequence. A sequence is no longer than 5 octets by definition.
+ * Thus passing a length greater than 5 to this function is an error. Encoding
+ * sequences shorter than 5 octets is supported and padding will be added to the
+ * output as per the specification.
+ */
+static void encode_sequence(const unsigned char *plain, int len, unsigned char *coded)
+{
+	assert(CHAR_BIT == 8);  // not sure this would work otherwise
+	assert(len >= 0 && len <= 5);
+
+	for (int block = 0; block < 8; block++) {
+		int octet = get_octet(block);  // figure out which octet this block starts in
+		int junk = get_offset(block);  // how many bits do we drop from this octet?
+
+		if (octet >= len) { // we hit the end of the buffer
+			pad(&coded[block], 8 - block);
+			return;
+		}
+
+		unsigned char c = shift_right(plain[octet], junk);  // first part
+
+		if (junk < 0  // is there a second part?
+		&&  octet < len - 1)  // is there still something to read?
+		{
+			c |= shift_right(plain[octet+1], 8 + junk);
+		}
+		coded[block] = encode_char(c);
+	}
+}
+
+void base32_encode(const unsigned char *plain, size_t len, unsigned char *coded)
+{
+	// All the hard work is done in encode_sequence(),
+	// here we just need to feed it the data sequence by sequence.
+	for (size_t i = 0, j = 0; i < len; i += 5, j += 8) {
+		encode_sequence(&plain[i], min(len - i, 5), &coded[j]);
+	}
+}
+
+static int decode_sequence(const unsigned char *coded, unsigned char *plain)
+{
+	assert(CHAR_BIT == 8);
+	assert(coded && plain);
+
+	plain[0] = 0;
+	for (int block = 0; block < 8; block++) {
+		int offset = get_offset(block);
+		int octet = get_octet(block);
+
+		int c = decode_char(coded[block]);
+		if (c < 0)  // invalid char, stop here
+			return octet;
+
+		plain[octet] |= shift_left(c, offset);
+		if (offset < 0) {  // does this block overflows to next octet?
+			assert(octet < 4);
+			plain[octet+1] = shift_left(c, 8 + offset);
+		}
+	}
+	return 5;
+}
+
+size_t base32_decode(const unsigned char *coded, unsigned char *plain)
+{
+	size_t written = 0;
+	for (size_t i = 0, j = 0; ; i += 8, j += 5) {
+		int n = decode_sequence(&coded[i], &plain[j]);
+		written += n;
+		if (n < 5)
+			return written;
+	}
+}