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# (gmp.info.gz) Number Theoretic Functions Info Catalog (gmp.info.gz) Integer Roots (gmp.info.gz) Integer Functions (gmp.info.gz) Integer Comparisons
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Number Theoretic Functions
==========================

- Function: int mpz_probab_prime_p (mpz_t N, int REPS)
Determine whether N is prime.  Return 2 if N is definitely prime,
return 1 if N is probably prime (without being certain), or return
0 if N is definitely composite.

This function does some trial divisions, then some Miller-Rabin
probabilistic primality tests.  REPS controls how many such tests
are done, 5 to 10 is a reasonable number, more will reduce the
chances of a composite being returned as "probably prime".

Miller-Rabin and similar tests can be more properly called
compositeness tests.  Numbers which fail are known to be composite
but those which pass might be prime or might be composite.  Only a
few composites pass, hence those which pass are considered
probably prime.

- Function: void mpz_nextprime (mpz_t ROP, mpz_t OP)
Set ROP to the next prime greater than OP.

This function uses a probabilistic algorithm to identify primes.
For practical purposes it's adequate, the chance of a composite
passing will be extremely small.

- Function: void mpz_gcd (mpz_t ROP, mpz_t OP1, mpz_t OP2)
Set ROP to the greatest common divisor of OP1 and OP2.  The result
is always positive even if one or both input operands are negative.

- Function: unsigned long int mpz_gcd_ui (mpz_t ROP, mpz_t OP1,
unsigned long int OP2)
Compute the greatest common divisor of OP1 and OP2.  If ROP is not
`NULL', store the result there.

If the result is small enough to fit in an `unsigned long int', it
is returned.  If the result does not fit, 0 is returned, and the
result is equal to the argument OP1.  Note that the result will
always fit if OP2 is non-zero.

- Function: void mpz_gcdext (mpz_t G, mpz_t S, mpz_t T, mpz_t A, mpz_t
B)
Set G to the greatest common divisor of A and B, and in addition
set S and T to coefficients satisfying A*S + B*T = G.  G is always
positive, even if one or both of A and B are negative.

If T is `NULL' then that value is not computed.

- Function: void mpz_lcm (mpz_t ROP, mpz_t OP1, mpz_t OP2)
- Function: void mpz_lcm_ui (mpz_t ROP, mpz_t OP1, unsigned long OP2)
Set ROP to the least common multiple of OP1 and OP2.  ROP is
always positive, irrespective of the signs of OP1 and OP2.  ROP
will be zero if either OP1 or OP2 is zero.

- Function: int mpz_invert (mpz_t ROP, mpz_t OP1, mpz_t OP2)
Compute the inverse of OP1 modulo OP2 and put the result in ROP.
If the inverse exists, the return value is non-zero and ROP will
satisfy 0 <= ROP < OP2.  If an inverse doesn't exist the return
value is zero and ROP is undefined.

- Function: int mpz_jacobi (mpz_t A, mpz_t B)
Calculate the Jacobi symbol (A/B).  This is defined only for B odd.

- Function: int mpz_legendre (mpz_t A, mpz_t P)
Calculate the Legendre symbol (A/P).  This is defined only for P
an odd positive prime, and for such P it's identical to the Jacobi
symbol.

- Function: int mpz_kronecker (mpz_t A, mpz_t B)
- Function: int mpz_kronecker_si (mpz_t A, long B)
- Function: int mpz_kronecker_ui (mpz_t A, unsigned long B)
- Function: int mpz_si_kronecker (long A, mpz_t B)
- Function: int mpz_ui_kronecker (unsigned long A, mpz_t B)
Calculate the Jacobi symbol (A/B) with the Kronecker extension
(a/2)=(2/a) when a odd, or (a/2)=0 when a even.

When B is odd the Jacobi symbol and Kronecker symbol are
identical, so `mpz_kronecker_ui' etc can be used for mixed
precision Jacobi symbols too.

example program `demos/qcn.c' which uses `mpz_kronecker_ui'.

- Function: unsigned long int mpz_remove (mpz_t ROP, mpz_t OP, mpz_t F)
Remove all occurrences of the factor F from OP and store the
result in ROP.  The return value is how many such occurrences were
removed.

- Function: void mpz_fac_ui (mpz_t ROP, unsigned long int OP)
Set ROP to OP!, the factorial of OP.

- Function: void mpz_bin_ui (mpz_t ROP, mpz_t N, unsigned long int K)
- Function: void mpz_bin_uiui (mpz_t ROP, unsigned long int N,
unsigned long int K)
Compute the binomial coefficient N over K and store the result in
ROP.  Negative values of N are supported by `mpz_bin_ui', using
the identity bin(-n,k) = (-1)^k * bin(n+k-1,k), see Knuth volume 1
section 1.2.6 part G.

- Function: void mpz_fib_ui (mpz_t FN, unsigned long int N)
- Function: void mpz_fib2_ui (mpz_t FN, mpz_t FNSUB1, unsigned long
int N)
`mpz_fib_ui' sets FN to to F[n], the N'th Fibonacci number.
`mpz_fib2_ui' sets FN to F[n], and FNSUB1 to F[n-1].

These functions are designed for calculating isolated Fibonacci
numbers.  When a sequence of values is wanted it's best to start
with `mpz_fib2_ui' and iterate the defining F[n+1]=F[n]+F[n-1] or
similar.

- Function: void mpz_lucnum_ui (mpz_t LN, unsigned long int N)
- Function: void mpz_lucnum2_ui (mpz_t LN, mpz_t LNSUB1, unsigned long
int N)
`mpz_lucnum_ui' sets LN to to L[n], the N'th Lucas number.
`mpz_lucnum2_ui' sets LN to L[n], and LNSUB1 to L[n-1].

These functions are designed for calculating isolated Lucas
numbers.  When a sequence of values is wanted it's best to start
with `mpz_lucnum2_ui' and iterate the defining L[n+1]=L[n]+L[n-1]
or similar.

The Fibonacci numbers and Lucas numbers are related sequences, so
it's never necessary to call both `mpz_fib2_ui' and
`mpz_lucnum2_ui'.  The formulas for going from Fibonacci to Lucas
can be found in  Lucas Numbers Algorithm, the reverse is
straightforward too.

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