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Annotation of OpenXM_contrib/gmp/mpz/lucnum2_ui.c, Revision 1.1

1.1     ! ohara       1: /* mpz_lucnum2_ui -- calculate Lucas numbers.
        !             2:
        !             3: Copyright 2001 Free Software Foundation, Inc.
        !             4:
        !             5: This file is part of the GNU MP Library.
        !             6:
        !             7: The GNU MP Library is free software; you can redistribute it and/or modify
        !             8: it under the terms of the GNU Lesser General Public License as published by
        !             9: the Free Software Foundation; either version 2.1 of the License, or (at your
        !            10: option) any later version.
        !            11:
        !            12: The GNU MP Library is distributed in the hope that it will be useful, but
        !            13: WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
        !            14: or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
        !            15: License for more details.
        !            16:
        !            17: You should have received a copy of the GNU Lesser General Public License
        !            18: along with the GNU MP Library; see the file COPYING.LIB.  If not, write to
        !            19: the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
        !            20: MA 02111-1307, USA. */
        !            21:
        !            22: #include <stdio.h>
        !            23: #include "gmp.h"
        !            24: #include "gmp-impl.h"
        !            25:
        !            26:
        !            27: void
        !            28: mpz_lucnum2_ui (mpz_ptr ln, mpz_ptr lnsub1, unsigned long n)
        !            29: {
        !            30:   mp_ptr     lp, l1p, f1p;
        !            31:   mp_size_t  size;
        !            32:   mp_limb_t  c;
        !            33:   TMP_DECL (marker);
        !            34:
        !            35:   ASSERT (ln != lnsub1);
        !            36:
        !            37:   /* handle small n quickly, and hide the special case for L[-1]=-1 */
        !            38:   if (n <= FIB_TABLE_LUCNUM_LIMIT)
        !            39:     {
        !            40:       mp_limb_t  f  = FIB_TABLE (n);
        !            41:       mp_limb_t  f1 = FIB_TABLE ((int) n - 1);
        !            42:
        !            43:       /* L[n] = F[n] + 2F[n-1] */
        !            44:       PTR(ln)[0] = f + 2*f1;
        !            45:       SIZ(ln) = 1;
        !            46:
        !            47:       /* L[n-1] = 2F[n] - F[n-1], but allow for L[-1]=-1 */
        !            48:       PTR(lnsub1)[0] = (n == 0 ? 1 : 2*f - f1);
        !            49:       SIZ(lnsub1) = (n == 0 ? -1 : 1);
        !            50:
        !            51:       return;
        !            52:     }
        !            53:
        !            54:   TMP_MARK (marker);
        !            55:   size = MPN_FIB2_SIZE (n);
        !            56:   f1p = TMP_ALLOC_LIMBS (size);
        !            57:
        !            58:   MPZ_REALLOC (ln,     size+1);
        !            59:   MPZ_REALLOC (lnsub1, size+1);
        !            60:   lp  = PTR(ln);
        !            61:   l1p = PTR(lnsub1);
        !            62:
        !            63:   size = mpn_fib2_ui (l1p, f1p, n);
        !            64:
        !            65:   /* L[n] = F[n] + 2F[n-1] */
        !            66:   c = mpn_lshift (lp, f1p, size, 1);
        !            67:   c += mpn_add_n (lp, lp, l1p, size);
        !            68:   lp[size] = c;
        !            69:   SIZ(ln) = size + (c != 0);
        !            70:
        !            71:   /* L[n-1] = 2F[n] - F[n-1] */
        !            72:   c = mpn_lshift (l1p, l1p, size, 1);
        !            73:   c -= mpn_sub_n (l1p, l1p, f1p, size);
        !            74:   ASSERT ((mp_limb_signed_t) c >= 0);
        !            75:   l1p[size] = c;
        !            76:   SIZ(lnsub1) = size + (c != 0);
        !            77:
        !            78:   TMP_FREE (marker);
        !            79: }