Add libgmp 6.2.0 to third_party
Don't build it yet. That will come in the next review.
Change-Id: Idf3266558165e5ab45f4a41c98cc8c838c8244d5
diff --git a/third_party/gmp/mpn/generic/brootinv.c b/third_party/gmp/mpn/generic/brootinv.c
new file mode 100644
index 0000000..e91b597
--- /dev/null
+++ b/third_party/gmp/mpn/generic/brootinv.c
@@ -0,0 +1,159 @@
+/* mpn_brootinv, compute r such that r^k * y = 1 (mod 2^b).
+
+ Contributed to the GNU project by Martin Boij (as part of perfpow.c).
+
+Copyright 2009, 2010, 2012, 2013, 2018 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"
+
+/* Computes a^2e (mod B). Uses right-to-left binary algorithm, since
+ typical use will have e small. */
+static mp_limb_t
+powsquaredlimb (mp_limb_t a, mp_limb_t e)
+{
+ mp_limb_t r;
+
+ r = 1;
+ /* if (LIKELY (e != 0)) */
+ do {
+ a *= a;
+ if (e & 1)
+ r *= a;
+ e >>= 1;
+ } while (e != 0);
+
+ return r;
+}
+
+/* Compute r such that r^k * y = 1 (mod B^n).
+
+ Iterates
+ r' <-- k^{-1} ((k+1) r - r^{k+1} y) (mod 2^b)
+ using Hensel lifting, each time doubling the number of known bits in r.
+
+ Works just for odd k. Else the Hensel lifting degenerates.
+
+ FIXME:
+
+ (1) Make it work for k == GMP_LIMB_MAX (k+1 below overflows).
+
+ (2) Rewrite iteration as
+ r' <-- r - k^{-1} r (r^k y - 1)
+ and take advantage of the zero low part of r^k y - 1.
+
+ (3) Use wrap-around trick.
+
+ (4) Use a small table to get starting value.
+
+ Scratch need: bn + (((bn + 1) >> 1) + 1) + scratch for mpn_powlo
+ Currently mpn_powlo requires 3*bn
+ so that 5*bn is surely enough, where bn = ceil (bnb / GMP_NUMB_BITS).
+*/
+
+void
+mpn_brootinv (mp_ptr rp, mp_srcptr yp, mp_size_t bn, mp_limb_t k, mp_ptr tp)
+{
+ mp_ptr tp2, tp3;
+ mp_limb_t kinv, k2, r0, y0;
+ mp_size_t order[GMP_LIMB_BITS + 1];
+ int d;
+
+ ASSERT (bn > 0);
+ ASSERT ((k & 1) != 0);
+
+ tp2 = tp + bn;
+ tp3 = tp + bn + ((bn + 3) >> 1);
+ k2 = (k >> 1) + 1; /* (k + 1) / 2 , but avoid k+1 overflow */
+
+ binvert_limb (kinv, k);
+
+ /* 4-bit initial approximation:
+
+ y%16 | 1 3 5 7 9 11 13 15,
+ k%4 +-------------------------+k2%2
+ 1 | 1 11 13 7 9 3 5 15 | 1
+ 3 | 1 3 5 7 9 11 13 15 | 0
+
+ */
+ y0 = yp[0];
+
+ r0 = y0 ^ (((y0 << 1) ^ (y0 << 2)) & (k2 << 3) & 8); /* 4 bits */
+ r0 = kinv * (k2 * r0 * 2 - y0 * powsquaredlimb(r0, k2 & 0x3f)); /* 8 bits */
+ r0 = kinv * (k2 * r0 * 2 - y0 * powsquaredlimb(r0, k2 & 0x3fff)); /* 16 bits */
+#if GMP_NUMB_BITS > 16
+ {
+ unsigned prec = 16;
+ do
+ {
+ r0 = kinv * (k2 * r0 * 2 - y0 * powsquaredlimb(r0, k2));
+ prec *= 2;
+ }
+ while (prec < GMP_NUMB_BITS);
+ }
+#endif
+
+ rp[0] = r0;
+ if (bn == 1)
+ return;
+
+ d = 0;
+ for (; bn != 2; bn = (bn + 1) >> 1)
+ order[d++] = bn;
+
+ order[d] = 2;
+ bn = 1;
+
+ do
+ {
+ mpn_sqr (tp, rp, bn); /* Result may overlap tp2 */
+ tp2[bn] = mpn_mul_1 (tp2, rp, bn, k2 << 1);
+
+ bn = order[d];
+
+ mpn_powlo (rp, tp, &k2, 1, bn, tp3);
+ mpn_mullo_n (tp, yp, rp, bn);
+
+ /* mpn_sub (tp, tp2, ((bn + 1) >> 1) + 1, tp, bn); */
+ /* The function above is not handled, ((bn + 1) >> 1) + 1 <= bn*/
+ {
+ mp_size_t pbn = (bn + 3) >> 1; /* Size of tp2 */
+ int borrow;
+ borrow = mpn_sub_n (tp, tp2, tp, pbn) != 0;
+ if (bn > pbn) /* 3 < bn */
+ {
+ if (borrow)
+ mpn_com (tp + pbn, tp + pbn, bn - pbn);
+ else
+ mpn_neg (tp + pbn, tp + pbn, bn - pbn);
+ }
+ }
+ mpn_pi1_bdiv_q_1 (rp, tp, bn, k, kinv, 0);
+ }
+ while (--d >= 0);
+}