--- /dev/null
+/* gcd_lehmer.c.
+
+ THE FUNCTIONS IN THIS FILE ARE INTERNAL WITH MUTABLE INTERFACES. IT IS ONLY
+ SAFE TO REACH THEM THROUGH DOCUMENTED INTERFACES. IN FACT, IT IS ALMOST
+ GUARANTEED THAT THEY'LL CHANGE OR DISAPPEAR IN A FUTURE GNU MP RELEASE.
+
+Copyright 2003, 2004, 2005, 2008 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 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.
+
+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 Lesser General Public
+License for more details.
+
+You should have received a copy of the GNU Lesser General Public License
+along with the GNU MP Library. If not, see http://www.gnu.org/licenses/. */
+
+#include "gmp.h"
+#include "gmp-impl.h"
+#include "longlong.h"
+
+/* Use binary algorithm to compute G <-- GCD (U, V) for usize, vsize == 2.
+ Both U and V must be odd. */
+static inline mp_size_t
+gcd_2 (mp_ptr gp, mp_srcptr up, mp_srcptr vp)
+{
+ mp_limb_t u0, u1, v0, v1;
+ mp_size_t gn;
+
+ u0 = up[0];
+ u1 = up[1];
+ v0 = vp[0];
+ v1 = vp[1];
+
+ ASSERT (u0 & 1);
+ ASSERT (v0 & 1);
+
+ /* Check for u0 != v0 needed to ensure that argument to
+ * count_trailing_zeros is non-zero. */
+ while (u1 != v1 && u0 != v0)
+ {
+ unsigned long int r;
+ if (u1 > v1)
+ {
+ u1 -= v1 + (u0 < v0);
+ u0 = (u0 - v0) & GMP_NUMB_MASK;
+ count_trailing_zeros (r, u0);
+ u0 = ((u1 << (GMP_NUMB_BITS - r)) & GMP_NUMB_MASK) | (u0 >> r);
+ u1 >>= r;
+ }
+ else /* u1 < v1. */
+ {
+ v1 -= u1 + (v0 < u0);
+ v0 = (v0 - u0) & GMP_NUMB_MASK;
+ count_trailing_zeros (r, v0);
+ v0 = ((v1 << (GMP_NUMB_BITS - r)) & GMP_NUMB_MASK) | (v0 >> r);
+ v1 >>= r;
+ }
+ }
+
+ gp[0] = u0, gp[1] = u1, gn = 1 + (u1 != 0);
+
+ /* If U == V == GCD, done. Otherwise, compute GCD (V, |U - V|). */
+ if (u1 == v1 && u0 == v0)
+ return gn;
+
+ v0 = (u0 == v0) ? ((u1 > v1) ? u1-v1 : v1-u1) : ((u0 > v0) ? u0-v0 : v0-u0);
+ gp[0] = mpn_gcd_1 (gp, gn, v0);
+
+ return 1;
+}
+
+/* Temporary storage: n */
+mp_size_t
+mpn_gcd_lehmer_n (mp_ptr gp, mp_ptr ap, mp_ptr bp, mp_size_t n, mp_ptr tp)
+{
+ /* Relax this requirement, and normalize at the start? Must disallow
+ A = B = 0, though. */
+ ASSERT(ap[n-1] > 0 || bp[n-1] > 0);
+
+ while (n > 2)
+ {
+ struct hgcd_matrix1 M;
+ mp_limb_t ah, al, bh, bl;
+ mp_limb_t mask;
+
+ mask = ap[n-1] | bp[n-1];
+ ASSERT (mask > 0);
+
+ if (mask & GMP_NUMB_HIGHBIT)
+ {
+ ah = ap[n-1]; al = ap[n-2];
+ bh = bp[n-1]; bl = bp[n-2];
+ }
+ else
+ {
+ int shift;
+
+ count_leading_zeros (shift, mask);
+ ah = MPN_EXTRACT_NUMB (shift, ap[n-1], ap[n-2]);
+ al = MPN_EXTRACT_NUMB (shift, ap[n-2], ap[n-3]);
+ bh = MPN_EXTRACT_NUMB (shift, bp[n-1], bp[n-2]);
+ bl = MPN_EXTRACT_NUMB (shift, bp[n-2], bp[n-3]);
+ }
+
+ /* Try an mpn_nhgcd2 step */
+ if (mpn_hgcd2 (ah, al, bh, bl, &M))
+ {
+ n = mpn_hgcd_mul_matrix1_inverse_vector (&M, tp, ap, bp, n);
+ MP_PTR_SWAP (ap, tp);
+ }
+ else
+ {
+ /* mpn_hgcd2 has failed. Then either one of a or b is very
+ small, or the difference is very small. Perform one
+ subtraction followed by one division. */
+ mp_size_t gn;
+
+ /* Temporary storage n */
+ n = mpn_gcd_subdiv_step (gp, &gn, ap, bp, n, tp);
+ if (n == 0)
+ return gn;
+ }
+ }
+
+ if (n == 1)
+ {
+ *gp = mpn_gcd_1(ap, 1, bp[0]);
+ return 1;
+ }
+
+ /* Due to the calling convention for mpn_gcd, at most one can be
+ even. */
+
+ if (! (ap[0] & 1))
+ MP_PTR_SWAP (ap, bp);
+
+ ASSERT (ap[0] & 1);
+
+ if (bp[0] == 0)
+ {
+ *gp = mpn_gcd_1 (ap, 2, bp[1]);
+ return 1;
+ }
+ else if (! (bp[0] & 1))
+ {
+ int r;
+ count_trailing_zeros (r, bp[0]);
+ bp[0] = ((bp[1] << (GMP_NUMB_BITS - r)) & GMP_NUMB_MASK) | (bp[0] >> r);
+ bp[1] >>= r;
+ }
+
+ return gcd_2(gp, ap, bp);
+}
projects / msp430-gcc.git / blobdiff