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authorDuncan Wilkie <antigravityd@gmail.com>2023-11-18 06:11:09 -0600
committerDuncan Wilkie <antigravityd@gmail.com>2023-11-18 06:11:09 -0600
commit11da511c784eca003deb90c23570f0873954e0de (patch)
treee14fdd3d5d6345956d67e79ae771d0633d28362b /gmp-6.3.0/mpn/generic/sec_div.c
Initial commit.
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+/* mpn_sec_div_qr, mpn_sec_div_r -- Compute Q = floor(U / V), U = U mod V.
+ Side-channel silent under the assumption that the used instructions are
+ side-channel silent.
+
+ Contributed to the GNU project by Torbjörn Granlund.
+
+Copyright 2011-2015 Free Software Foundation, Inc.
+
+This file is part of the GNU MP Library.
+
+The GNU MP Library is free software; you can redistribute it and/or modify
+it under the terms of either:
+
+ * the GNU Lesser General Public License as published by the Free
+ Software Foundation; either version 3 of the License, or (at your
+ option) any later version.
+
+or
+
+ * the GNU General Public License as published by the Free Software
+ Foundation; either version 2 of the License, or (at your option) any
+ later version.
+
+or both in parallel, as here.
+
+The GNU MP Library is distributed in the hope that it will be useful, but
+WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+for more details.
+
+You should have received copies of the GNU General Public License and the
+GNU Lesser General Public License along with the GNU MP Library. If not,
+see https://www.gnu.org/licenses/. */
+
+#include "gmp-impl.h"
+#include "longlong.h"
+
+#if OPERATION_sec_div_qr
+#define FNAME mpn_sec_div_qr
+#define FNAME_itch mpn_sec_div_qr_itch
+#define Q(q) q,
+#define RETTYPE mp_limb_t
+#endif
+#if OPERATION_sec_div_r
+#define FNAME mpn_sec_div_r
+#define FNAME_itch mpn_sec_div_r_itch
+#define Q(q)
+#define RETTYPE void
+#endif
+
+mp_size_t
+FNAME_itch (mp_size_t nn, mp_size_t dn)
+{
+#if OPERATION_sec_div_qr
+/* Needs (nn + dn + 1) + mpn_sec_pi1_div_qr's needs of (2nn' - dn + 1) for a
+ total of 3nn + 4 limbs at tp. Note that mpn_sec_pi1_div_qr's nn is one
+ greater than ours, therefore +4 and not just +2. */
+ return 3 * nn + 4;
+#endif
+#if OPERATION_sec_div_r
+/* Needs (nn + dn + 1) + mpn_sec_pi1_div_r's needs of (dn + 1) for a total of
+ nn + 2dn + 2 limbs at tp. */
+ return nn + 2 * dn + 2;
+#endif
+}
+
+RETTYPE
+FNAME (Q(mp_ptr qp)
+ mp_ptr np, mp_size_t nn,
+ mp_srcptr dp, mp_size_t dn,
+ mp_ptr tp)
+{
+ mp_limb_t d1, d0;
+ unsigned int cnt;
+ mp_limb_t inv32;
+
+ ASSERT (dn >= 1);
+ ASSERT (nn >= dn);
+ ASSERT (dp[dn - 1] != 0);
+
+ d1 = dp[dn - 1];
+ count_leading_zeros (cnt, d1);
+
+ if (cnt != 0)
+ {
+ mp_limb_t qh, cy;
+ mp_ptr np2, dp2;
+ dp2 = tp; /* dn limbs */
+ mpn_lshift (dp2, dp, dn, cnt);
+
+ np2 = tp + dn; /* (nn + 1) limbs */
+ cy = mpn_lshift (np2, np, nn, cnt);
+ np2[nn++] = cy;
+
+ d0 = dp2[dn - 1];
+ d0 += (~d0 != 0);
+ invert_limb (inv32, d0);
+
+ /* We add nn + dn to tp here, not nn + 1 + dn, as expected. This is
+ since nn here will have been incremented. */
+#if OPERATION_sec_div_qr
+ qh = mpn_sec_pi1_div_qr (np2 + dn, np2, nn, dp2, dn, inv32, tp + nn + dn);
+ ASSERT (qh == 0); /* FIXME: this indicates inefficiency! */
+ MPN_COPY (qp, np2 + dn, nn - dn - 1);
+ qh = np2[nn - 1];
+#else
+ mpn_sec_pi1_div_r (np2, nn, dp2, dn, inv32, tp + nn + dn);
+#endif
+
+ mpn_rshift (np, np2, dn, cnt);
+
+#if OPERATION_sec_div_qr
+ return qh;
+#endif
+ }
+ else
+ {
+ /* FIXME: Consider copying np => np2 here, adding a 0-limb at the top.
+ That would simplify the underlying pi1 function, since then it could
+ assume nn > dn. */
+ d0 = dp[dn - 1];
+ d0 += (~d0 != 0);
+ invert_limb (inv32, d0);
+
+#if OPERATION_sec_div_qr
+ return mpn_sec_pi1_div_qr (qp, np, nn, dp, dn, inv32, tp);
+#else
+ mpn_sec_pi1_div_r (np, nn, dp, dn, inv32, tp);
+#endif
+ }
+}