/* $OpenBSD: bn_shift.c,v 1.18 2023/01/05 04:51:13 jsing Exp $ */
/* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
 * All rights reserved.
 *
 * This package is an SSL implementation written
 * by Eric Young (eay@cryptsoft.com).
 * The implementation was written so as to conform with Netscapes SSL.
 *
 * This library is free for commercial and non-commercial use as long as
 * the following conditions are aheared to.  The following conditions
 * apply to all code found in this distribution, be it the RC4, RSA,
 * lhash, DES, etc., code; not just the SSL code.  The SSL documentation
 * included with this distribution is covered by the same copyright terms
 * except that the holder is Tim Hudson (tjh@cryptsoft.com).
 *
 * Copyright remains Eric Young's, and as such any Copyright notices in
 * the code are not to be removed.
 * If this package is used in a product, Eric Young should be given attribution
 * as the author of the parts of the library used.
 * This can be in the form of a textual message at program startup or
 * in documentation (online or textual) provided with the package.
 *
 * 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 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. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *    "This product includes cryptographic software written by
 *     Eric Young (eay@cryptsoft.com)"
 *    The word 'cryptographic' can be left out if the rouines from the library
 *    being used are not cryptographic related :-).
 * 4. If you include any Windows specific code (or a derivative thereof) from
 *    the apps directory (application code) you must include an acknowledgement:
 *    "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"
 *
 * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``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 THE AUTHOR OR 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.
 *
 * The licence and distribution terms for any publically available version or
 * derivative of this code cannot be changed.  i.e. this code cannot simply be
 * copied and put under another distribution licence
 * [including the GNU Public Licence.]
 */

#include <stdio.h>
#include <string.h>

#include <openssl/err.h>

#include "bn_local.h"

int
BN_lshift1(BIGNUM *r, const BIGNUM *a)
{
	BN_ULONG *ap, *rp, t, c;
	int i;


	if (r != a) {
		r->neg = a->neg;
		if (!bn_wexpand(r, a->top + 1))
			return (0);
		r->top = a->top;
	} else {
		if (!bn_wexpand(r, a->top + 1))
			return (0);
	}
	ap = a->d;
	rp = r->d;
	c = 0;
	for (i = 0; i < a->top; i++) {
		t= *(ap++);
		*(rp++) = ((t << 1) | c) & BN_MASK2;
		c = (t & BN_TBIT) ? 1 : 0;
	}
	if (c) {
		*rp = 1;
		r->top++;
	}
	return (1);
}

int
BN_rshift1(BIGNUM *r, const BIGNUM *a)
{
	BN_ULONG *ap, *rp, t, c;
	int i, j;


	if (BN_is_zero(a)) {
		BN_zero(r);
		return (1);
	}
	i = a->top;
	ap = a->d;
	j = i - (ap[i - 1]==1);
	if (a != r) {
		if (!bn_wexpand(r, j))
			return (0);
		r->neg = a->neg;
	}
	rp = r->d;
	t = ap[--i];
	c = (t & 1) ? BN_TBIT : 0;
	if (t >>= 1)
		rp[i] = t;
	while (i > 0) {
		t = ap[--i];
		rp[i] = ((t >> 1) & BN_MASK2) | c;
		c = (t & 1) ? BN_TBIT : 0;
	}
	r->top = j;
	return (1);
}

int
BN_lshift(BIGNUM *r, const BIGNUM *a, int n)
{
	int i, nw, lb, rb;
	BN_ULONG *t, *f;
	BN_ULONG l;

	if (n < 0) {
		BNerror(BN_R_INVALID_LENGTH);
		return 0;
	}


	r->neg = a->neg;
	nw = n / BN_BITS2;
	if (!bn_wexpand(r, a->top + nw + 1))
		return (0);
	lb = n % BN_BITS2;
	rb = BN_BITS2 - lb;
	f = a->d;
	t = r->d;
	t[a->top + nw] = 0;
	if (lb == 0)
		for (i = a->top - 1; i >= 0; i--)
			t[nw + i] = f[i];
	else
		for (i = a->top - 1; i >= 0; i--) {
			l = f[i];
			t[nw + i + 1] |= (l >> rb) & BN_MASK2;
			t[nw + i] = (l << lb) & BN_MASK2;
		}
	memset(t, 0, nw * sizeof(t[0]));
/*	for (i=0; i<nw; i++)
		t[i]=0;*/
	r->top = a->top + nw + 1;
	bn_correct_top(r);
	return (1);
}

int
BN_rshift(BIGNUM *r, const BIGNUM *a, int n)
{
	size_t count, shift_bits, shift_words;
	size_t lshift, rshift;
	ssize_t lstride;
	BN_ULONG *dst, *src;
	size_t i;

	if (n < 0) {
		BNerror(BN_R_INVALID_LENGTH);
		return 0;
	}
	shift_bits = n;

	/*
	 * Right bit shift, potentially across word boundaries.
	 *
	 * When shift is not an exact multiple of BN_BITS2, the top bits of
	 * the next word need to be left shifted and combined with the right
	 * shifted bits using bitwise OR. If shift is an exact multiple of
	 * BN_BITS2, the source for the left and right shifts are the same
	 * and the shifts become zero (which is effectively a memmove).
	 */
	shift_words = shift_bits / BN_BITS2;
	rshift = shift_bits % BN_BITS2;
	lshift = (BN_BITS2 - rshift) % BN_BITS2;
	lstride = (lshift + rshift) / BN_BITS2;

	if (a->top <= shift_words) {
		BN_zero(r);
		return 1;
	}
	count = a->top - shift_words;

	if (!bn_wexpand(r, count))
		return 0;

	src = a->d + shift_words;
	dst = r->d;

	for (i = 1; i < count; i++) {
		*dst = src[lstride] << lshift | *src >> rshift;
		src++;
		dst++;
	}
	*dst = *src >> rshift;

	r->top = count;
	r->neg = a->neg;

	bn_correct_top(r);

	return 1;
}