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author | Richard Maw <richard.maw@codethink.co.uk> | 2012-01-17 14:43:55 +0000 |
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committer | Richard Maw <richard.maw@codethink.co.uk> | 2012-01-17 14:43:55 +0000 |
commit | 2de9abc5c9d40b3c716307d67d16146f823fd554 (patch) | |
tree | 6979db67934ddc8b564150b465846a383b428ff8 /gnulib/lib/gcd.c | |
parent | 33cc1c6fda6e72a7bae1401e9b2cec495a4d3ff1 (diff) | |
download | patch-baserock/bootstrap.tar.gz |
add the output of bootstrapbaserock/bootstrap-pass2baserock/bootstrap
Diffstat (limited to 'gnulib/lib/gcd.c')
m--------- | gnulib | 0 | ||||
-rw-r--r-- | gnulib/lib/gcd.c | 87 |
2 files changed, 87 insertions, 0 deletions
diff --git a/gnulib b/gnulib deleted file mode 160000 -Subproject 443bc5ffcf7429e557f4a371b0661abe98ddbc1 diff --git a/gnulib/lib/gcd.c b/gnulib/lib/gcd.c new file mode 100644 index 0000000..50c60df --- /dev/null +++ b/gnulib/lib/gcd.c @@ -0,0 +1,87 @@ +/* Arithmetic. + Copyright (C) 2001-2002, 2006, 2009-2011 Free Software Foundation, Inc. + Written by Bruno Haible <bruno@clisp.org>, 2001. + + This program is free software: you can redistribute it and/or modify + it under the terms of the GNU General Public License as published by + the Free Software Foundation; either version 3 of the License, or + (at your option) any later version. + + This program 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 a copy of the GNU General Public License + along with this program. If not, see <http://www.gnu.org/licenses/>. */ + +#include <config.h> + +/* This file can also be used to define gcd functions for other unsigned + types, such as 'unsigned long long' or 'uintmax_t'. */ +#ifndef WORD_T +/* Specification. */ +# include "gcd.h" +# define WORD_T unsigned long +# define GCD gcd +#endif + +#include <stdlib.h> + +/* Return the greatest common divisor of a > 0 and b > 0. */ +WORD_T +GCD (WORD_T a, WORD_T b) +{ + /* Why no division, as in Euclid's algorithm? Because in Euclid's algorithm + the division result floor(a/b) or floor(b/a) is very often = 1 or = 2, + and nearly always < 8. A sequence of a few subtractions and tests is + faster than a division. */ + /* Why not Euclid's algorithm? Because the two integers can be shifted by 1 + bit in a single instruction, and the algorithm uses fewer variables than + Euclid's algorithm. */ + + WORD_T c = a | b; + c = c ^ (c - 1); + /* c = largest power of 2 that divides a and b. */ + + if (a & c) + { + if (b & c) + goto odd_odd; + else + goto odd_even; + } + else + { + if (b & c) + goto even_odd; + else + abort (); + } + + for (;;) + { + odd_odd: /* a/c and b/c both odd */ + if (a == b) + break; + if (a > b) + { + a = a - b; + even_odd: /* a/c even, b/c odd */ + do + a = a >> 1; + while ((a & c) == 0); + } + else + { + b = b - a; + odd_even: /* a/c odd, b/c even */ + do + b = b >> 1; + while ((b & c) == 0); + } + } + + /* a = b */ + return a; +} |