The smod kernel of type residual ( residual )

Definition

Type residual::smod is a variant of class residual::mod that uses a signed representation. Here numbers modulo p are represented by integral doubles in (- p/2, + p/2). All functions have the common precondition that p is a prime between 3 and 2²⁶. The functions of type residual::mod are also provided for class residual::smod and have the same meaning, so we do not list them separately here.

#include < LEDA/residual.h >

Operations

double

residual::frac(double a)

returns a + z where z is the unique integer such that a + z $\in$ [- 1/2, 1/2)

Creation

residual	x	creates an instance x of type residual and initializes it with zero.
residual	x(long a)	creates an instance x of type residual and initializes it with the value of a.
residual	x(int a)	creates an instance x of type residual and initializes it with the value of a.
residual	x(double a)	creates an instance x of type residual and initializes it with the integral part of x.
residual	x(integer a)	creates an instance x of type residual and initializes it with the value of a.

Operations

int	residual::set_maximal_bit_length(int b, bool with_check=do_overflow_check)
		sets the maximal bit size of the representable numbers to b and returns the previous maximal bit size
int	residual::get_maximal_bit_length()
		returns the maximal bit size of the representable numbers
int	residual::required_primetable_size(int b)
		returns the number of primes required to represent signed numbers up to bit length b

The following functions have the common precondition that the residual objects a, x are integral and do not overflow.

integer	x.to_integer()	returns the integer equal to x.
long	x.length()	returns the length of the binary representation of the integer represented by x.
bool	x.is_long()	returns true if and only if x fits in the data format long.
long	x.to_long()	returns a long number which is initialized with the value of x. Precondition x.is_long() is true.
double	x.to_double()	returns a double floating point approximation of x.
double	x.to_float()	as above.
bool	x.is_zero()	returns true if and only if x is equal to zero.
bool	x.is_invertible()	returns true if and only if x is nonzero and the current modular representation of x allows to invert x without loss of information.
int	x.sign()	returns the sign of x.
int	x.lagrange_sign()	returns the sign of x using Lagrange's formula.
int	x.garner_sign()	returns the sign of x using Garner's formula.
number_string	x.to_string()	returns the decimal representation of x.
residual	abs(residual a)	returns the absolute value of a
void	x.absolute(residual a)	sets x to the absolute value of a.

The remaining functions do not have implicit preconditions. Although not explicitly mentioned, the arithmetic operations +, -, *, /, +=, -=, *=, /=, + +, - -, the shift operations, the comparison operations <, <=, >, >=, ==, != and the stream operations are available.

residual	sqr(residual a)	returns a*a
residual	det2x2(residual a, residual b, residual c, residual d)
		returns a*d-b*c
void	x.add(residual a, residual b)
		sets x to a+b.
void	x.sub(residual a, residual b)
		sets x to a-b.
void	x.mul(residual a, residual b)
		sets x to a*b.
void	x.div(residual a, residual b)
		sets x to a/b.
void	x.det2x2(residual a, residual b, residual c, residual d)
		sets x to a*d-b*c.
void	x.inverse(residual a)	sets x to the modular inverse of a. Precondition x.in_invertible is true.
void	x.negate(residual a)	sets x to -a.

The following functions provide direct read-only access to the internal representation of residual objects. They should only be used by the experienced user after reading the full documentation of type residual.

residual_sequence	residual::get_primetable()
		returns a copy of the currently used primetable
residual_sequence	residual::get_garnertable()
		returns a copy of the currently used table of Garner's constants
residual_sequence	get_representation()	returns a copy of the residual sequence representing x