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Diffstat (limited to 'rts/gmp/mpn/generic/scan0.c')
-rw-r--r-- | rts/gmp/mpn/generic/scan0.c | 62 |
1 files changed, 62 insertions, 0 deletions
diff --git a/rts/gmp/mpn/generic/scan0.c b/rts/gmp/mpn/generic/scan0.c new file mode 100644 index 0000000000..96f05ce854 --- /dev/null +++ b/rts/gmp/mpn/generic/scan0.c @@ -0,0 +1,62 @@ +/* mpn_scan0 -- Scan from a given bit position for the next clear bit. + +Copyright (C) 1994, 1996 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 2.1 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; see the file COPYING.LIB. If not, write to +the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, +MA 02111-1307, USA. */ + +#include "gmp.h" +#include "gmp-impl.h" +#include "longlong.h" + +/* Design issues: + 1. What if starting_bit is not within U? Caller's problem? + 2. Bit index should be 'unsigned'? + + Argument constraints: + 1. U must sooner ot later have a limb with a clear bit. + */ + +unsigned long int +#if __STDC__ +mpn_scan0 (register mp_srcptr up, + register unsigned long int starting_bit) +#else +mpn_scan0 (up, starting_bit) + register mp_srcptr up; + register unsigned long int starting_bit; +#endif +{ + mp_size_t starting_word; + mp_limb_t alimb; + int cnt; + mp_srcptr p; + + /* Start at the word implied by STARTING_BIT. */ + starting_word = starting_bit / BITS_PER_MP_LIMB; + p = up + starting_word; + alimb = ~*p++; + + /* Mask off any bits before STARTING_BIT in the first limb. */ + alimb &= - (mp_limb_t) 1 << (starting_bit % BITS_PER_MP_LIMB); + + while (alimb == 0) + alimb = ~*p++; + + count_leading_zeros (cnt, alimb & -alimb); + return (p - up) * BITS_PER_MP_LIMB - 1 - cnt; +} |