--- /dev/null
+/* mpz_scan1 -- search for a 1 bit.
+
+Copyright 2000, 2001, 2002, 2004 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"
+
+
+/* mpn_scan0 can't be used for the inverted u<0 search since there might not
+ be a 0 bit before the end of the data. mpn_scan1 could be used under u>0
+ (except when in the high limb), but usually the search won't go very far
+ so it seems reasonable to inline that code. */
+
+unsigned long
+mpz_scan1 (mpz_srcptr u, unsigned long starting_bit)
+{
+ mp_srcptr u_ptr = PTR(u);
+ mp_size_t size = SIZ(u);
+ mp_size_t abs_size = ABS(size);
+ mp_srcptr u_end = u_ptr + abs_size;
+ unsigned long starting_limb = starting_bit / GMP_NUMB_BITS;
+ mp_srcptr p = u_ptr + starting_limb;
+ mp_limb_t limb;
+ int cnt;
+
+ /* Past the end there's no 1 bits for u>=0, or an immediate 1 bit for u<0.
+ Notice this test picks up any u==0 too. */
+ if (starting_limb >= abs_size)
+ return (size >= 0 ? ULONG_MAX : starting_bit);
+
+ limb = *p;
+
+ if (size >= 0)
+ {
+ /* Mask to 0 all bits before starting_bit, thus ignoring them. */
+ limb &= (MP_LIMB_T_MAX << (starting_bit % GMP_NUMB_BITS));
+
+ if (limb == 0)
+ {
+ /* If it's the high limb which is zero after masking, then there's
+ no 1 bits after starting_bit. */
+ p++;
+ if (p == u_end)
+ return ULONG_MAX;
+
+ /* Otherwise search further for a non-zero limb. The high limb is
+ non-zero, if nothing else. */
+ for (;;)
+ {
+ limb = *p;
+ if (limb != 0)
+ break;
+ p++;
+ ASSERT (p < u_end);
+ }
+ }
+ }
+ else
+ {
+ mp_srcptr q;
+
+ /* If there's a non-zero limb before ours then we're in the ones
+ complement region. Search from *(p-1) downwards since that might
+ give better cache locality, and since a non-zero in the middle of a
+ number is perhaps a touch more likely than at the end. */
+ q = p;
+ while (q != u_ptr)
+ {
+ q--;
+ if (*q != 0)
+ goto inverted;
+ }
+
+ if (limb == 0)
+ {
+ /* Skip zero limbs, to find the start of twos complement. The
+ high limb is non-zero, if nothing else. This search is
+ necessary so the -limb is applied at the right spot. */
+ do
+ {
+ p++;
+ ASSERT (p < u_end);
+ limb = *p;
+ }
+ while (limb == 0);
+
+ /* Apply twos complement, and look for a 1 bit in that. Since
+ limb!=0 here, also have (-limb)!=0 so there's certainly a 1
+ bit. */
+ limb = -limb;
+ goto got_limb;
+ }
+
+ /* Adjust so ~limb implied by searching for 0 bit becomes -limb. */
+ limb--;
+
+ inverted:
+ /* Now seeking a 0 bit. */
+
+ /* Mask to 1 all bits before starting_bit, thus ignoring them. */
+ limb |= (CNST_LIMB(1) << (starting_bit % GMP_NUMB_BITS)) - 1;
+
+ /* Search for a limb which is not all ones. If the end is reached
+ then the zero immediately past the end is the result. */
+ while (limb == GMP_NUMB_MAX)
+ {
+ p++;
+ if (p == u_end)
+ return abs_size * GMP_NUMB_BITS;
+ limb = *p;
+ }
+
+ /* Now seeking low 1 bit. */
+ limb = ~limb;
+ }
+
+ got_limb:
+ ASSERT (limb != 0);
+ count_trailing_zeros (cnt, limb);
+ return (p - u_ptr) * GMP_NUMB_BITS + cnt;
+}
projects / msp430-gcc.git / blobdiff