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diff --git a/gnulib b/gnulib deleted file mode 160000 -Subproject 4fc10daa05477586fea99b6b3ca02a87d1102fa diff --git a/gnulib/doc/gcd.texi b/gnulib/doc/gcd.texi new file mode 100644 index 00000000..52bd5ecd --- /dev/null +++ b/gnulib/doc/gcd.texi @@ -0,0 +1,54 @@ +@node gcd +@section gcd: greatest common divisor +@findex gcd + +@c Copyright (C) 2006, 2009, 2010 Free Software Foundation, Inc. + +@c Permission is granted to copy, distribute and/or modify this document +@c under the terms of the GNU Free Documentation License, Version 1.3 or +@c any later version published by the Free Software Foundation; with no +@c Invariant Sections, with no Front-Cover Texts, and with no Back-Cover +@c Texts. A copy of the license is included in the ``GNU Free +@c Documentation License'' file as part of this distribution. + +The @code{gcd} function returns the greatest common divisor of two numbers +@code{a > 0} and @code{b > 0}. It is the caller's responsibility to ensure +that the arguments are non-zero. + +If you need a gcd function for an integer type larger than +@samp{unsigned long}, you can include the @file{gcd.c} implementation file +with parametrization. The parameters are: + +@itemize @bullet +@item WORD_T +Define this to the unsigned integer type that you need this function for. + +@item GCD +Define this to the name of the function to be created. +@end itemize + +The created function has the prototype +@smallexample +WORD_T GCD (WORD_T a, WORD_T b); +@end smallexample + +If you need the least common multiple of two numbers, it can be computed +like this: @code{lcm(a,b) = (a / gcd(a,b)) * b} or +@code{lcm(a,b) = a * (b / gcd(a,b))}. +Avoid the formula @code{lcm(a,b) = (a * b) / gcd(a,b)} because - although +mathematically correct - it can yield a wrong result, due to integer overflow. + +In some applications it is useful to have a function taking the gcd of two +signed numbers. In this case, the gcd function result is usually normalized +to be non-negative (so that two gcd results can be compared in magnitude +or compared against 1, etc.). Note that in this case the prototype of the +function has to be +@smallexample +unsigned long gcd (long a, long b); +@end smallexample +and not +@smallexample +long gcd (long a, long b); +@end smallexample +because @code{gcd(LONG_MIN,LONG_MIN) = -LONG_MIN = LONG_MAX + 1} does not +fit into a signed @samp{long}. |