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mpi: Same computation for square and multiply for mpi_pow.

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* mpi/mpi-pow.c (_gcry_mpi_powm): Compare msize for max_u_size.  Move
the assignment to base_u into the loop.  Copy content refered by RP to
BASE_U except the last of the loop.

--

Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>

(backport commit of libgcrypt master:
78130828e9a140a9de4dafadbc844dbb64cb709a)
This commit is contained in:
NIIBE Yutaka 2017-07-07 14:38:19 +09:00
parent b38f4489f7
commit 12029f83fd
1 changed files with 38 additions and 34 deletions
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48
mpi/mpi-pow.c
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@ -387,6 +387,9 @@ mpi_powm (MPI res, MPI base, MPI expo, MPI mod)
size = 2 * msize;
msign = mod->sign;
ep = expo->d;
MPN_NORMALIZE(ep, esize);
if (esize * BITS_PER_MPI_LIMB > 512)
W = 5;
else if (esize * BITS_PER_MPI_LIMB > 256)
@ -403,7 +406,6 @@ mpi_powm (MPI res, MPI base, MPI expo, MPI mod)
bsec = mpi_is_secure(base);
rp = res->d;
ep = expo->d;
if (!msize)
msize = 1 / msize; /* provoke a signal */
@ -463,7 +465,8 @@ mpi_powm (MPI res, MPI base, MPI expo, MPI mod)
}
/* Make BASE, EXPO and MOD not overlap with RES. */
/* Make BASE, EXPO not overlap with RES. We don't need to check MOD
because that has already been copied to the MP var. */
if ( rp == bp )
{
/* RES and BASE are identical. Allocate temp. space for BASE. */
@ -477,13 +480,6 @@ mpi_powm (MPI res, MPI base, MPI expo, MPI mod)
ep = ep_marker = mpi_alloc_limb_space( esize, esec );
MPN_COPY(ep, rp, esize);
}
if ( rp == mp )
{
/* RES and MOD are identical. Allocate temporary space for MOD.*/
assert (!mp_marker);
mp = mp_marker = mpi_alloc_limb_space( msize, msec );
MPN_COPY(mp, rp, msize);
}
/* Copy base to the result. */
if (res->alloced < size)
@ -529,7 +525,10 @@ mpi_powm (MPI res, MPI base, MPI expo, MPI mod)
MPN_COPY (precomp[i], rp, rsize);
}
if (msize > max_u_size)
max_u_size = msize;
base_u = mpi_alloc_limb_space (max_u_size, esec);
MPN_ZERO (base_u, max_u_size);
i = esize - 1;
@ -574,6 +573,10 @@ mpi_powm (MPI res, MPI base, MPI expo, MPI mod)
{
int c0;
mpi_limb_t e0;
struct gcry_mpi w, u;
w.sign = u.sign = 0;
w.flags = u.flags = 0;
w.d = base_u;
count_leading_zeros (c0, e);
e = (e << c0);
@ -582,7 +585,7 @@ mpi_powm (MPI res, MPI base, MPI expo, MPI mod)
e0 = (e >> (BITS_PER_MPI_LIMB - W));
if (c >= W)
c0 =0;
c0 = 0;
else
{
if ( --i < 0 )
@ -607,30 +610,31 @@ mpi_powm (MPI res, MPI base, MPI expo, MPI mod)
count_trailing_zeros (c0, e0);
e0 = (e0 >> c0) >> 1;
for (j += W - c0; j >= 0; j--)
{
/*
* base_u <= precomp[e0]
* base_u_size <= precomp_size[e0];
* base_u_size <= precomp_size[e0]
*/
base_u_size = 0;
for (k = 0; k < (1<< (W - 1)); k++)
{
struct gcry_mpi w, u;
w.alloced = w.nlimbs = precomp_size[k];
u.alloced = u.nlimbs = precomp_size[k];
w.nbits = w.nlimbs * BITS_PER_MPI_LIMB;
u.nbits = u.nlimbs * BITS_PER_MPI_LIMB;
w.sign = u.sign = 0;
w.flags = u.flags = 0;
w.d = base_u;
u.d = precomp[k];
mpi_set_cond (&w, &u, k == e0);
base_u_size |= ( precomp_size[k] & ((mpi_size_t)0 - (k == e0)) );
base_u_size |= ( precomp_size[k] & (0UL - (k == e0)) );
}
for (j += W - c0; j >= 0; j--)
{
mul_mod (xp, &xsize, rp, rsize,
j == 0 ? base_u : rp, j == 0 ? base_u_size : rsize,
w.alloced = w.nlimbs = rsize;
u.alloced = u.nlimbs = rsize;
u.d = rp;
mpi_set_cond (&w, &u, j != 0);
base_u_size ^= ((base_u_size ^ rsize) & (0UL - (j != 0)));
mul_mod (xp, &xsize, rp, rsize, base_u, base_u_size,
mp, msize, &karactx);
tp = rp; rp = xp; xp = tp;
rsize = xsize;