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/mpf/pow_ui.c b/third_party/gmp/mpf/pow_ui.c
new file mode 100644
index 0000000..8d54dc0
--- /dev/null
+++ b/third_party/gmp/mpf/pow_ui.c
@@ -0,0 +1,83 @@
+/* mpf_pow_ui -- Compute b^e.
+
+Copyright 1998, 1999, 2001, 2012, 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"
+
+/* This uses a plain right-to-left square-and-multiply algorithm.
+
+ FIXME: When popcount(e) is not too small, it would probably speed things up
+ to use a k-ary sliding window algorithm. */
+
+void
+mpf_pow_ui (mpf_ptr r, mpf_srcptr b, unsigned long int e)
+{
+ mpf_t t;
+ int cnt;
+
+ if (e <= 1)
+ {
+ if (e == 0)
+ mpf_set_ui (r, 1);
+ else
+ mpf_set (r, b);
+ return;
+ }
+
+ count_leading_zeros (cnt, (mp_limb_t) e);
+ cnt = GMP_LIMB_BITS - 1 - cnt;
+
+ /* Increase computation precision as a function of the exponent. Adding
+ log2(popcount(e) + log2(e)) bits should be sufficient, but we add log2(e),
+ i.e. much more. With mpf's rounding of precision to whole limbs, this
+ will be excessive only when limbs are artificially small. */
+ mpf_init2 (t, mpf_get_prec (r) + cnt);
+
+ mpf_set (t, b); /* consume most significant bit */
+ while (--cnt > 0)
+ {
+ mpf_mul (t, t, t);
+ if ((e >> cnt) & 1)
+ mpf_mul (t, t, b);
+ }
+
+ /* Do the last iteration specially in order to save a copy operation. */
+ if (e & 1)
+ {
+ mpf_mul (t, t, t);
+ mpf_mul (r, t, b);
+ }
+ else
+ {
+ mpf_mul (r, t, t);
+ }
+
+ mpf_clear (t);
+}