/*	$NetBSD: n-fold.c,v 1.2 2017/01/28 21:31:49 christos Exp $	*/

/*
 * Copyright (c) 1999 Kungliga Tekniska Högskolan
 * (Royal Institute of Technology, Stockholm, Sweden).
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * 3. Neither the name of KTH nor the names of its contributors may be
 *    used to endorse or promote products derived from this software without
 *    specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY KTH AND ITS CONTRIBUTORS ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL KTH OR ITS CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
 * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
 * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. */

#include "krb5_locl.h"

static void
rr13(uint8_t *dst1, uint8_t *dst2, uint8_t *src, size_t len)
{
    int bytes = (len + 7) / 8;
    int i;
    const int bits = 13 % len;

    for (i = 0; i < bytes; i++) {
	int bb;
	int b1, s1, b2, s2;
	/* calculate first bit position of this byte */
	bb = 8 * i - bits;
	while(bb < 0)
	    bb += len;
	/* byte offset and shift count */
	b1 = bb / 8;
	s1 = bb % 8;

	if (bb + 8 > bytes * 8)
	    /* watch for wraparound */
	    s2 = (len + 8 - s1) % 8;
	else
	    s2 = 8 - s1;
	b2 = (b1 + 1) % bytes;
	dst1[i] = (src[b1] << s1) | (src[b2] >> s2);
	dst2[i] = dst1[i];
    }

    return;
}

/*
 * Add `b' to `a', both being one's complement numbers.
 * This function assumes that inputs *a, *b are aligned
 * to 4 bytes.
 */
static void
add1(uint8_t *a, uint8_t *b, size_t len)
{
    int i;
    int carry = 0;
    uint32_t x;
    uint32_t left, right;

    for (i = len - 1; (i+1) % 4; i--) {
	x = a[i] + b[i] + carry;
	carry = x > 0xff;
	a[i] = x & 0xff;
    }

    for (i = len / 4 - 1; i >= 0; i--) {
	left = ntohl(((uint32_t *)a)[i]);
	right = ntohl(((uint32_t *)b)[i]);
	x = left + right + carry;
	carry = x < left || x < right;
	((uint32_t *)a)[i]  = x;
    }

    for (i = len - 1; (i+1) % 4; i--) {
	x = a[i] + carry;
	carry = x > 0xff;
	a[i] = x & 0xff;
    }

    for (i = len / 4 - 1; carry && i >= 0; i--) {
        left = ((uint32_t *)a)[i];
        x = left + carry;
        carry = x < left;
        ((uint32_t *)a)[i] = x;
    }

    for (i = len / 4 - 1; i >=0; i--)
        ((uint32_t *)a)[i] = htonl(((uint32_t *)a)[i]);
}

KRB5_LIB_FUNCTION krb5_error_code KRB5_LIB_CALL
_krb5_n_fold(const void *str, size_t len, void *key, size_t size)
{
    /* if len < size we need at most N * len bytes, ie < 2 * size;
       if len > size we need at most 2 * len */
    size_t maxlen = 2 * max(size, len);
    size_t l = 0;
    uint8_t *tmp;
    uint8_t *tmpbuf;
    uint8_t *buf1;
    uint8_t *buf2;

    tmp = malloc(maxlen + 2 * len);
    if (tmp == NULL)
        return ENOMEM;

    buf1 = tmp + maxlen;
    buf2 = tmp + maxlen + len;

    memset(key, 0, size);
    memcpy(buf1, str, len);
    memcpy(tmp, buf1, len);
    do {
	l += len;
	while(l >= size) {
	    add1(key, tmp, size);
	    l -= size;
	    if(l == 0)
		break;
	    memmove(tmp, tmp + size, l);
	}
	rr13(tmp + l, buf2, buf1, len * 8);
	tmpbuf = buf1;
	buf1 = buf2;
	buf2 = tmpbuf;
    } while(l != 0);

    memset(tmp, 0, maxlen + 2 * len);
    free(tmp);
    return 0;
}