/* rp[n-1..0] = bp[bn-1..0] ^ ep[en-1..0] mod mp[n-1..0]
Requires that mp[n-1..0] is odd. FIXME: is this true?
Requires that ep[en-1..0] is > 1.
Uses scratch space at tp of 3n+1 limbs. */
void
mpn_powm_sec (mp_ptr rp, mp_srcptr bp, mp_size_t bn,
mp_srcptr ep, mp_size_t en,
mp_srcptr mp, mp_size_t n, mp_ptr tp)
{
mp_limb_t minv;
int cnt;
mp_bitcnt_t ebi;
int windowsize, this_windowsize;
mp_limb_t expbits;
mp_ptr pp, this_pp;
long i;
int cnd;
ASSERT (en > 1 || (en == 1 && ep[0] > 0));
ASSERT (n >= 1 && ((mp[0] & 1) != 0));
count_leading_zeros (cnt, ep[en - 1]);
ebi = (mp_bitcnt_t) en * GMP_LIMB_BITS - cnt;
windowsize = win_size (ebi);
binvert_limb (minv, mp[0]);
minv = -minv;
pp = tp + 4 * n;
this_pp = pp;
this_pp[n] = 1;
redcify (this_pp, this_pp + n, 1, mp, n, tp + 6 * n);
this_pp += n;
redcify (this_pp, bp, bn, mp, n, tp + 6 * n);
/* Precompute powers of b and put them in the temporary area at pp. */
for (i = (1 << windowsize) - 2; i > 0; i--)
{
mpn_mul_basecase (tp, this_pp, n, pp + n, n);
this_pp += n;
mpn_redc_1_sec (this_pp, tp, mp, n, minv);
}
expbits = getbits (ep, ebi, windowsize);
if (ebi < windowsize)
ebi = 0;
else
ebi -= windowsize;
#if WANT_CACHE_SECURITY
mpn_tabselect (rp, pp, n, 1 << windowsize, expbits);
#else
MPN_COPY (rp, pp + n * expbits, n);
#endif
while (ebi != 0)
{
expbits = getbits (ep, ebi, windowsize);
this_windowsize = windowsize;
if (ebi < windowsize)
{
this_windowsize -= windowsize - ebi;
ebi = 0;
}
else
ebi -= windowsize;
do
{
mpn_local_sqr (tp, rp, n, tp + 2 * n);
mpn_redc_1_sec (rp, tp, mp, n, minv);
this_windowsize--;
}
while (this_windowsize != 0);
#if WANT_CACHE_SECURITY
mpn_tabselect (tp + 2*n, pp, n, 1 << windowsize, expbits);
mpn_mul_basecase (tp, rp, n, tp + 2*n, n);
#else
mpn_mul_basecase (tp, rp, n, pp + n * expbits, n);
#endif
mpn_redc_1_sec (rp, tp, mp, n, minv);
}
MPN_COPY (tp, rp, n);
MPN_ZERO (tp + n, n);
mpn_redc_1_sec (rp, tp, mp, n, minv);
cnd = mpn_sub_n (tp, rp, mp, n); /* we need just retval */
mpn_subcnd_n (rp, rp, mp, n, !cnd);
}
/* rp[n-1..0] = bp[bn-1..0] ^ ep[en-1..0] mod mp[n-1..0]
Requires that mp[n-1..0] is odd.
Requires that ep[en-1..0] is > 1.
Uses scratch space tp[3n..0], i.e., 3n+1 words. */
void
mpn_powm_sec (mp_ptr rp, mp_srcptr bp, mp_size_t bn,
mp_srcptr ep, mp_size_t en,
mp_srcptr mp, mp_size_t n, mp_ptr tp)
{
mp_limb_t mip[2];
int cnt;
long ebi;
int windowsize, this_windowsize;
mp_limb_t expbits;
mp_ptr pp, this_pp, last_pp;
long i;
int redc_x;
TMP_DECL;
ASSERT (en > 1 || (en == 1 && ep[0] > 1));
ASSERT (n >= 1 && ((mp[0] & 1) != 0));
TMP_MARK;
count_leading_zeros (cnt, ep[en - 1]);
ebi = en * GMP_LIMB_BITS - cnt;
windowsize = win_size (ebi);
if (BELOW_THRESHOLD (n, REDC_2_THRESHOLD))
{
binvert_limb (mip[0], mp[0]);
mip[0] = -mip[0];
redc_x = 1;
}
#if defined (HAVE_NATIVE_mpn_addmul_2)
else
{
mpn_binvert (mip, mp, 2, tp);
mip[0] = -mip[0]; mip[1] = ~mip[1];
redc_x = 2;
}
#endif
#if 0
mpn_binvert (mip, mp, n, tp);
redc_x = 0;
#endif
pp = TMP_ALLOC_LIMBS (n << windowsize);
this_pp = pp;
this_pp[n] = 1;
redcify (this_pp, this_pp + n, 1, mp, n);
this_pp += n;
redcify (this_pp, bp, bn, mp, n);
/* Precompute powers of b and put them in the temporary area at pp. */
for (i = (1 << windowsize) - 2; i > 0; i--)
{
last_pp = this_pp;
this_pp += n;
mpn_mul_n (tp, last_pp, pp + n, n);
MPN_REDC_X (this_pp, tp, mp, n, mip);
}
expbits = getbits (ep, ebi, windowsize);
ebi -= windowsize;
if (ebi < 0)
ebi = 0;
MPN_COPY (rp, pp + n * expbits, n);
while (ebi != 0)
{
expbits = getbits (ep, ebi, windowsize);
ebi -= windowsize;
this_windowsize = windowsize;
if (ebi < 0)
{
this_windowsize += ebi;
ebi = 0;
}
do
{
mpn_sqr_n (tp, rp, n);
MPN_REDC_X (rp, tp, mp, n, mip);
this_windowsize--;
}
while (this_windowsize != 0);
#if WANT_CACHE_SECURITY
mpn_tabselect (tp + 2*n, pp, n, 1 << windowsize, expbits);
mpn_mul_n (tp, rp, tp + 2*n, n);
#else
mpn_mul_n (tp, rp, pp + n * expbits, n);
#endif
MPN_REDC_X (rp, tp, mp, n, mip);
}
MPN_COPY (tp, rp, n);
MPN_ZERO (tp + n, n);
MPN_REDC_X (rp, tp, mp, n, mip);
if (mpn_cmp (rp, mp, n) >= 0)
mpn_sub_n (rp, rp, mp, n);
TMP_FREE;
}
