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The greatest common divisor (GCD) of integers a and b, at least one of which is nonzero, is the greatest positive integer d such that d is a divisor of both a and b; that is, there are integers e and f such that a = de and b = df, and d is the largest such integer.
Synonyms for GCD include greatest common factor (GCF), highest common factor (HCF), highest common divisor (HCD), and greatest common measure (GCM). The greatest common divisor is often written as gcd( a , b ) or, more simply, as ( a , b ) , [ 3 ] although the latter notation is ambiguous, also used for concepts such as an ideal in the ring of ...
Visualisation of using the binary GCD algorithm to find the greatest common divisor (GCD) of 36 and 24. Thus, the GCD is 2 2 × 3 = 12.. The binary GCD algorithm, also known as Stein's algorithm or the binary Euclidean algorithm, [1] [2] is an algorithm that computes the greatest common divisor (GCD) of two nonnegative integers.
Factoring out the gcd's from the coefficients, we can write = ′ and = ′ where the gcds of the coefficients of ′, ′ are both 1. Clearly, it is enough to prove the assertion when f , g {\displaystyle f,g} are replaced by f ′ , g ′ {\displaystyle f',g'} ; thus, we assume the gcd's of the coefficients of f , g {\displaystyle f,g} are ...
Use the extended Euclidean algorithm to compute k −1, the modular multiplicative inverse of k mod 2 w, where w is the number of bits in a word. This inverse will exist since the numbers are odd and the modulus has no odd factors. For each number in the list, multiply it by k −1 and take the least significant word of the result.
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Lehmer's GCD algorithm, named after Derrick Henry Lehmer, is a fast GCD algorithm, an improvement on the simpler but slower Euclidean algorithm. It is mainly used for big integers that have a representation as a string of digits relative to some chosen numeral system base , say β = 1000 or β = 2 32 .
In other words, every GCD domain is a Schreier domain. For every pair of elements x, y of a GCD domain R, a GCD d of x and y and an LCM m of x and y can be chosen such that dm = xy, or stated differently, if x and y are nonzero elements and d is any GCD d of x and y, then xy/d is an LCM of x and y, and vice versa.