/**
 * copyright 2002, 2003 Bryce "Zooko" Wilcox-O'Hearn
 * mailto:zooko@zooko.com
 *
 * See the end of this file for the free software, open source license (BSD-style).
 */
#include "zbase32.h"

#include <math.h>
#include <string.h>
#include <stdlib.h>
#include <stdio.h> /* XXX only for debug printfs */

static const char*const chars="ybndrfg8ejkmcpqxot1uwisza345h769";

/* Types from zstr */
/**
 * A zstr is simply an unsigned int length and a pointer to a buffer of
 * unsigned chars.
 */
typedef struct {
	size_t len; /* the length of the string (not counting the null-terminating character) */
	unsigned char* buf; /* pointer to the first byte */
} zstr;

/**
 * A zstr is simply an unsigned int length and a pointer to a buffer of
 * const unsigned chars.
 */
typedef struct {
	size_t len; /* the length of the string (not counting the null-terminating character) */
	const unsigned char* buf; /* pointer to the first byte */
} czstr;

/* Functions from zstr */
static zstr
new_z(const size_t len)
{
	zstr result;
	result.buf = (unsigned char *)malloc(len+1);
	if (result.buf == NULL) {
		result.len = 0;
		return result;
	}
	result.len = len;
	result.buf[len] = '\0';
	return result;
}

/* Functions from zutil */
static size_t
divceil(size_t n, size_t d)
{
	return n/d+((n%d)!=0);
}

static zstr b2a_l_extra_Duffy(const czstr os, const size_t lengthinbits)
{
	zstr result = new_z(divceil(os.len*8, 5)); /* if lengthinbits is not a multiple of 8 then this is allocating space for 0, 1, or 2 extra quintets that will be truncated at the end of this function if they are not needed */
	if (result.buf == NULL)
		return result;

	unsigned char* resp = result.buf + result.len; /* pointer into the result buffer, initially pointing to the "one-past-the-end" quintet */
	const unsigned char* osp = os.buf + os.len; /* pointer into the os buffer, initially pointing to the "one-past-the-end" octet */

	/* Now this is a real live Duff's device.  You gotta love it. */
	unsigned long x=0; /* to hold up to 32 bits worth of the input */
	switch ((osp - os.buf) % 5) {
	case 0:
		do {
			x = *--osp;
			*--resp = chars[x % 32]; /* The least sig 5 bits go into the final quintet. */
			x /= 32; /* ... now we have 3 bits worth in x... */
	case 4:
			x |= ((unsigned long)(*--osp)) << 3; /* ... now we have 11 bits worth in x... */
			*--resp = chars[x % 32];
			x /= 32; /* ... now we have 6 bits worth in x... */
			*--resp = chars[x % 32];
			x /= 32; /* ... now we have 1 bits worth in x... */
	case 3:
			x |= ((unsigned long)(*--osp)) << 1; /* The 8 bits from the 2-indexed octet.  So now we have 9 bits worth in x... */
			*--resp = chars[x % 32];
			x /= 32; /* ... now we have 4 bits worth in x... */
	case 2:
			x |= ((unsigned long)(*--osp)) << 4; /* The 8 bits from the 1-indexed octet.  So now we have 12 bits worth in x... */
			*--resp = chars[x%32];
			x /= 32; /* ... now we have 7 bits worth in x... */
			*--resp = chars[x%32];
			x /= 32; /* ... now we have 2 bits worth in x... */
	case 1:
			x |= ((unsigned long)(*--osp)) << 2; /* The 8 bits from the 0-indexed octet.  So now we have 10 bits worth in x... */
			*--resp = chars[x%32];
			x /= 32; /* ... now we have 5 bits worth in x... */
			*--resp = chars[x];
		} while (osp > os.buf);
	} /* switch ((osp - os.buf) % 5) */

	/* truncate any unused trailing zero quintets */
	result.len = divceil(lengthinbits, 5);
	result.buf[result.len] = '\0';
	return result;
}

static zstr b2a_l(const czstr os, const size_t lengthinbits)
{
		return b2a_l_extra_Duffy(os, lengthinbits);
}

static zstr b2a(const czstr os)
{
	return b2a_l(os, os.len*8);
}

char *
zbase32_encode(const unsigned char *data, size_t length)
{
	czstr input = { length, data };
	zstr output = b2a(input);
	return (char *)output.buf;
}

/**
 * Copyright (c) 2002 Bryce "Zooko" Wilcox-O'Hearn
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software to deal in this software without restriction, including
 * without limitation the rights to use, copy, modify, merge, publish,
 * distribute, sublicense, and/or sell copies of this software, and to permit
 * persons to whom this 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 this software.
 * 
 * THIS 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 THIS SOFTWARE OR THE USE OR OTHER DEALINGS IN 
 * THIS SOFTWARE.
 */
