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This commit is contained in:
457
externals/libressl/crypto/bn/bn_div.c
vendored
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457
externals/libressl/crypto/bn/bn_div.c
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/* $OpenBSD: bn_div.c,v 1.40 2023/03/27 10:21:23 tb Exp $ */
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/* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
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* All rights reserved.
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*
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* This package is an SSL implementation written
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* by Eric Young (eay@cryptsoft.com).
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* The implementation was written so as to conform with Netscapes SSL.
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*
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* This library is free for commercial and non-commercial use as long as
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* the following conditions are aheared to. The following conditions
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* apply to all code found in this distribution, be it the RC4, RSA,
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* lhash, DES, etc., code; not just the SSL code. The SSL documentation
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* included with this distribution is covered by the same copyright terms
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* except that the holder is Tim Hudson (tjh@cryptsoft.com).
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*
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* Copyright remains Eric Young's, and as such any Copyright notices in
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* the code are not to be removed.
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* If this package is used in a product, Eric Young should be given attribution
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* as the author of the parts of the library used.
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* This can be in the form of a textual message at program startup or
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* in documentation (online or textual) provided with the package.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. All advertising materials mentioning features or use of this software
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* must display the following acknowledgement:
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* "This product includes cryptographic software written by
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* Eric Young (eay@cryptsoft.com)"
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* The word 'cryptographic' can be left out if the rouines from the library
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* being used are not cryptographic related :-).
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* 4. If you include any Windows specific code (or a derivative thereof) from
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* the apps directory (application code) you must include an acknowledgement:
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* "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"
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*
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* THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* The licence and distribution terms for any publically available version or
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* derivative of this code cannot be changed. i.e. this code cannot simply be
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* copied and put under another distribution licence
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* [including the GNU Public Licence.]
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*/
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#include <assert.h>
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#include <stdio.h>
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#include <openssl/opensslconf.h>
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#include <openssl/bn.h>
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#include <openssl/err.h>
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#include "bn_arch.h"
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#include "bn_local.h"
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#include "bn_internal.h"
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BN_ULONG bn_div_3_words(const BN_ULONG *m, BN_ULONG d1, BN_ULONG d0);
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#ifndef HAVE_BN_DIV_WORDS
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#if defined(BN_LLONG) && defined(BN_DIV2W)
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BN_ULONG
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bn_div_words(BN_ULONG h, BN_ULONG l, BN_ULONG d)
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{
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return ((BN_ULONG)(((((BN_ULLONG)h) << BN_BITS2)|l)/(BN_ULLONG)d));
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}
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#else
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/* Divide h,l by d and return the result. */
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/* I need to test this some more :-( */
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BN_ULONG
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bn_div_words(BN_ULONG h, BN_ULONG l, BN_ULONG d)
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{
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BN_ULONG dh, dl, q,ret = 0, th, tl, t;
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int i, count = 2;
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if (d == 0)
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return (BN_MASK2);
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i = BN_num_bits_word(d);
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assert((i == BN_BITS2) || (h <= (BN_ULONG)1 << i));
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i = BN_BITS2 - i;
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if (h >= d)
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h -= d;
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if (i) {
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d <<= i;
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h = (h << i) | (l >> (BN_BITS2 - i));
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l <<= i;
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}
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dh = (d & BN_MASK2h) >> BN_BITS4;
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dl = (d & BN_MASK2l);
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for (;;) {
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if ((h >> BN_BITS4) == dh)
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q = BN_MASK2l;
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else
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q = h / dh;
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th = q * dh;
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tl = dl * q;
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for (;;) {
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t = h - th;
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if ((t & BN_MASK2h) ||
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((tl) <= (
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(t << BN_BITS4) |
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((l & BN_MASK2h) >> BN_BITS4))))
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break;
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q--;
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th -= dh;
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tl -= dl;
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}
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t = (tl >> BN_BITS4);
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tl = (tl << BN_BITS4) & BN_MASK2h;
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th += t;
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if (l < tl)
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th++;
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l -= tl;
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if (h < th) {
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h += d;
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q--;
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}
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h -= th;
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if (--count == 0)
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break;
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ret = q << BN_BITS4;
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h = ((h << BN_BITS4) | (l >> BN_BITS4)) & BN_MASK2;
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l = (l & BN_MASK2l) << BN_BITS4;
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}
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ret |= q;
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return (ret);
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}
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#endif /* !defined(BN_LLONG) && defined(BN_DIV2W) */
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#endif
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/*
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* Divide a double word (h:l) by d, returning the quotient q and the remainder
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* r, such that q * d + r is equal to the numerator.
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*/
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#ifndef HAVE_BN_DIV_REM_WORDS
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#ifndef HAVE_BN_DIV_REM_WORDS_INLINE
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static inline void
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bn_div_rem_words_inline(BN_ULONG h, BN_ULONG l, BN_ULONG d, BN_ULONG *out_q,
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BN_ULONG *out_r)
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{
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BN_ULONG q, r;
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q = bn_div_words(h, l, d);
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r = (l - q * d) & BN_MASK2;
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*out_q = q;
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*out_r = r;
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}
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#endif
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void
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bn_div_rem_words(BN_ULONG h, BN_ULONG l, BN_ULONG d, BN_ULONG *out_q,
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BN_ULONG *out_r)
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{
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bn_div_rem_words_inline(h, l, d, out_q, out_r);
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}
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#endif
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#ifndef HAVE_BN_DIV_3_WORDS
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/*
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* Interface is somewhat quirky, |m| is pointer to most significant limb,
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* and less significant limb is referred at |m[-1]|. This means that caller
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* is responsible for ensuring that |m[-1]| is valid. Second condition that
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* has to be met is that |d0|'s most significant bit has to be set. Or in
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* other words divisor has to be "bit-aligned to the left." The subroutine
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* considers four limbs, two of which are "overlapping," hence the name...
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*/
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BN_ULONG
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bn_div_3_words(const BN_ULONG *m, BN_ULONG d1, BN_ULONG d0)
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{
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BN_ULONG n0, n1, q, t2h, t2l;
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BN_ULONG rem = 0;
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n0 = m[0];
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n1 = m[-1];
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if (n0 == d0)
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return BN_MASK2;
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/* n0 < d0 */
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bn_div_rem_words(n0, n1, d0, &q, &rem);
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bn_mulw(d1, q, &t2h, &t2l);
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for (;;) {
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if (t2h < rem || (t2h == rem && t2l <= m[-2]))
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break;
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q--;
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rem += d0;
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if (rem < d0)
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break; /* don't let rem overflow */
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if (t2l < d1)
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t2h--;
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t2l -= d1;
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}
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return q;
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}
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#endif /* !HAVE_BN_DIV_3_WORDS */
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/*
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* BN_div_internal computes quotient := numerator / divisor, rounding towards
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* zero and setting remainder such that quotient * divisor + remainder equals
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* the numerator. Thus:
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*
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* quotient->neg == numerator->neg ^ divisor->neg (unless result is zero)
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* remainder->neg == numerator->neg (unless the remainder is zero)
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*
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* If either the quotient or remainder is NULL, the respective value is not
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* returned.
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*/
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static int
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BN_div_internal(BIGNUM *quotient, BIGNUM *remainder, const BIGNUM *numerator,
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const BIGNUM *divisor, BN_CTX *ctx, int ct)
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{
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int norm_shift, i, loop, r_neg;
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BIGNUM *tmp, wnum, *snum, *sdiv, *res;
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BN_ULONG *resp, *wnump;
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BN_ULONG d0, d1;
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int num_n, div_n;
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int no_branch = 0;
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int ret = 0;
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BN_CTX_start(ctx);
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/* Invalid zero-padding would have particularly bad consequences. */
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if (numerator->top > 0 && numerator->d[numerator->top - 1] == 0) {
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BNerror(BN_R_NOT_INITIALIZED);
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goto err;
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}
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if (ct)
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no_branch = 1;
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if (BN_is_zero(divisor)) {
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BNerror(BN_R_DIV_BY_ZERO);
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goto err;
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}
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if (!no_branch) {
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if (BN_ucmp(numerator, divisor) < 0) {
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if (remainder != NULL) {
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if (!bn_copy(remainder, numerator))
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goto err;
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}
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if (quotient != NULL)
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BN_zero(quotient);
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goto done;
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}
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}
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if ((tmp = BN_CTX_get(ctx)) == NULL)
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goto err;
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if ((snum = BN_CTX_get(ctx)) == NULL)
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goto err;
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if ((sdiv = BN_CTX_get(ctx)) == NULL)
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goto err;
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if ((res = quotient) == NULL) {
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if ((res = BN_CTX_get(ctx)) == NULL)
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goto err;
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}
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/* First we normalise the numbers. */
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norm_shift = BN_BITS2 - BN_num_bits(divisor) % BN_BITS2;
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if (!BN_lshift(sdiv, divisor, norm_shift))
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goto err;
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sdiv->neg = 0;
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norm_shift += BN_BITS2;
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if (!BN_lshift(snum, numerator, norm_shift))
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goto err;
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snum->neg = 0;
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if (no_branch) {
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/*
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* Since we don't know whether snum is larger than sdiv, we pad
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* snum with enough zeroes without changing its value.
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*/
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if (snum->top <= sdiv->top + 1) {
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if (!bn_wexpand(snum, sdiv->top + 2))
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goto err;
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for (i = snum->top; i < sdiv->top + 2; i++)
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snum->d[i] = 0;
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snum->top = sdiv->top + 2;
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} else {
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if (!bn_wexpand(snum, snum->top + 1))
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goto err;
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snum->d[snum->top] = 0;
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snum->top++;
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}
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}
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div_n = sdiv->top;
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num_n = snum->top;
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loop = num_n - div_n;
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/*
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* Setup a 'window' into snum - this is the part that corresponds to the
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* current 'area' being divided.
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*/
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wnum.neg = 0;
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wnum.d = &(snum->d[loop]);
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wnum.top = div_n;
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/* only needed when BN_ucmp messes up the values between top and max */
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wnum.dmax = snum->dmax - loop; /* so we don't step out of bounds */
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wnum.flags = snum->flags | BN_FLG_STATIC_DATA;
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/* Get the top 2 words of sdiv */
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/* div_n=sdiv->top; */
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d0 = sdiv->d[div_n - 1];
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d1 = (div_n == 1) ? 0 : sdiv->d[div_n - 2];
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/* pointer to the 'top' of snum */
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wnump = &(snum->d[num_n - 1]);
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/* Setup to 'res' */
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if (!bn_wexpand(res, (loop + 1)))
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goto err;
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res->top = loop - no_branch;
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r_neg = numerator->neg ^ divisor->neg;
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resp = &(res->d[loop - 1]);
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/* space for temp */
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if (!bn_wexpand(tmp, (div_n + 1)))
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goto err;
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if (!no_branch) {
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if (BN_ucmp(&wnum, sdiv) >= 0) {
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bn_sub_words(wnum.d, wnum.d, sdiv->d, div_n);
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*resp = 1;
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} else
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res->top--;
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}
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/*
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* If res->top == 0 then clear the neg value otherwise decrease the resp
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* pointer.
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*/
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if (res->top == 0)
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res->neg = 0;
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else
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resp--;
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for (i = 0; i < loop - 1; i++, wnump--, resp--) {
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BN_ULONG q, l0;
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/*
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* The first part of the loop uses the top two words of snum and
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* sdiv to calculate a BN_ULONG q such that:
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*
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* | wnum - sdiv * q | < sdiv
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*/
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q = bn_div_3_words(wnump, d1, d0);
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l0 = bn_mul_words(tmp->d, sdiv->d, div_n, q);
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tmp->d[div_n] = l0;
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wnum.d--;
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/*
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* Ignore top values of the bignums just sub the two BN_ULONG
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* arrays with bn_sub_words.
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*/
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if (bn_sub_words(wnum.d, wnum.d, tmp->d, div_n + 1)) {
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/*
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* Note: As we have considered only the leading two
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* BN_ULONGs in the calculation of q, sdiv * q might be
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* greater than wnum (but then (q-1) * sdiv is less or
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* equal than wnum).
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*/
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q--;
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if (bn_add_words(wnum.d, wnum.d, sdiv->d, div_n)) {
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/*
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* We can't have an overflow here (assuming
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* that q != 0, but if q == 0 then tmp is
|
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* zero anyway).
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*/
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(*wnump)++;
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}
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}
|
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/* store part of the result */
|
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*resp = q;
|
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}
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bn_correct_top(snum);
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if (remainder != NULL) {
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/*
|
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* Keep a copy of the neg flag in numerator because if
|
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* remainder == numerator, BN_rshift() will overwrite it.
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*/
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int neg = numerator->neg;
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BN_rshift(remainder, snum, norm_shift);
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BN_set_negative(remainder, neg);
|
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}
|
||||
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if (no_branch)
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bn_correct_top(res);
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BN_set_negative(res, r_neg);
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done:
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ret = 1;
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err:
|
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BN_CTX_end(ctx);
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return ret;
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}
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||||
int
|
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BN_div(BIGNUM *quotient, BIGNUM *remainder, const BIGNUM *numerator,
|
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const BIGNUM *divisor, BN_CTX *ctx)
|
||||
{
|
||||
int ct;
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||||
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||||
ct = BN_get_flags(numerator, BN_FLG_CONSTTIME) != 0 ||
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||||
BN_get_flags(divisor, BN_FLG_CONSTTIME) != 0;
|
||||
|
||||
return BN_div_internal(quotient, remainder, numerator, divisor, ctx, ct);
|
||||
}
|
||||
|
||||
int
|
||||
BN_div_nonct(BIGNUM *quotient, BIGNUM *remainder, const BIGNUM *numerator,
|
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const BIGNUM *divisor, BN_CTX *ctx)
|
||||
{
|
||||
return BN_div_internal(quotient, remainder, numerator, divisor, ctx, 0);
|
||||
}
|
||||
|
||||
int
|
||||
BN_div_ct(BIGNUM *quotient, BIGNUM *remainder, const BIGNUM *numerator,
|
||||
const BIGNUM *divisor, BN_CTX *ctx)
|
||||
{
|
||||
return BN_div_internal(quotient, remainder, numerator, divisor, ctx, 1);
|
||||
}
|
||||
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