CONFORMS TO

SVID 3, POSIX, BSD 4.3, ISO 9899

SEE ALSO

date(1), gettimeofday(2), time(2), tzset(3),
difftime(3), strftime(3), newctime(3)

BSD, 26 April 1996

difftime

difftime—Calculates time difference

SYNOPSIS

#include <time.h>
double difftime(time_t time1, time_t time0);

DESCRIPTION

The difftime() function returns the number of seconds elapsed between time time1 and time time0. The two times are specified in calendar time, which represents the time elapsed since 00:00:00 on January 1, 1970, Coordinated Universal Time (UTC).

CONFORMS TO

SVID 3, BSD 4.3, ISO 9899

SEE ALSO

date(1), gettimeofday(2), time(2), ctime(3),
gmtime(3), localtime(3)

div

div—Computes the quotient and remainder of integer division

SYNOPSIS

#include <stdlib.h>
div_t div(int numer, int denom);

DESCRIPTION

The div() function computes the value numer/denom and returns the quotient and remainder in a structure named div_t that contains two integer members named quot and rem.

RETURN VALUE

The div_t structure.

CONFORMS TO

SVID 3, BSD 4.3, ISO 9899

SEE ALSO

ldiv(3)

6 June 1993

drand48, erand48, lrand48, nrand48, mrand48, jrand48, srand48, seed48, lcong48

drand48, erand48, lrand48, nrand48, mrand48,
jrand48, srand48, seed48, lcong48—Generate uniformly distributed
pseudo-random numbers

SYNOPSIS

#include <stdlib.h>
double   drand48(void);
double   erand48(unsigned short int xsubi[3]);
long     int lrand48(void);
long     int nrand48(unsigned short int xsubi[3]);
long     int mrand48(void);
long     int jrand48(unsigned short int xsubi[3]);
void     srand48(long int seedval);
unsigned  short int * seed48(unsigned short int seed16v [3]);
void     lcong48(unsigned short int param[7]);

These functions generate pseudo-random numbers using the linear congruential algorithm and 48-bit integer arithmetic.

The drand48() and erand48() functions return non-negative double-precision floating-point values uniformly distributed between [0.0, 1.0].

The lrand48() and nrand48() functions return non-negative long integers uniformly distributed between 0 and 2^31.

The mrand48() and jrand48() functions return signed long integers uniformly distributed between _2^31 and 2^31.

The srand48(),seed48(), and lcong48() functions are initialization functions, one of which should be called before using drand48(), lrand48(), or mrand49(). The functions erand48(), nrand48(), and jrand48() do not require an initialization function to be called first.

All the functions work by generating a sequence of 48-bit integers, Xi, according to the linear congruential formula

Xi+1=(aXi+c) mod m, where i >=0

The parameter m=2^48; hence 48-bit integer arithmetic is performed. Unless lcong48() is called, a and c are given by

a = 0x5DEECE66D
c = 0xB

The value returned by any of the functions drand48(), erand48(), lrand48(), nrand48(), mrand48(), or jrand48() is computed by first generating the next 48-bit Xi in the sequence. Then the appropriate number of bits, according to the type of data item to be returned, is copied from the high-order bits of Xi and transformed into the returned value.

The functions drand48(), lrand48(), and mrand48() store the last 48-bit Xi generated in an internal buffer. The functions erand48(), nrand48(), and jrand48() require the calling program to provide storage for the successive Xi values in the array argument xsubi. The functions are initialized by placing the initial value of Xi into the array before calling the function for the first time.

The initializer function srand48() sets the high-order 32 bits of Xi to the argument seedval. The low-order 16 bits are set to the arbitrary value 0x330E.

The initializer function seed48() sets the value of Xi to the 48-bit value specified in the array argument seed16v. The previous value of Xi is copied into an internal buffer and a pointer to this buffer is returned by seed48().

The initialization function lcong48() allows the user to specify initial values for Xi, a and c. Array argument elements param[0-2] specify Xi, param[3-5] specify a, and param[6] specifies c. After lcong48() has been called, a subsequent call to either srand48() or seed48() will restore the standard values of a and c.

CONFORMS TO

SVID 3

NOTES

These functions are declared obsolete by SVID 3, which states that rand(3) should be used instead.

SEE ALSO

rand(3), random(3)

2 July 1993

drem

drem—Floating-point remainder function

#include <math.h>
double drem(double x, double y);

The drem() function computes the remainder of dividing x by y. The return value is x_n*y, where n is the quotient of x divided by y, rounded to the nearest integer. If the quotient is ¹¦₂, it is rounded to the even number.

The drem() function returns the remainder unless y is 0, in which case the function fails and errno is set.

EDOM        The denominator y is 0.

BSD 4.3

fmod(3)

6 June 1993

ecvt, fcvt

ecvt, fcvt—Convert a floating-point number to a string

#include    <stdlib.h>
char        *ecvt(double    number,   size_t   ndigits,int*decpt,int*sign);
char        *fcvt(double    number,   size_t   ndigits,int*decpt,int*sign);

The ecvt() function converts number to a NULL-terminated string of ndigits digits and returns a pointer to the string. The string itself does not contain a decimal point; however, the position of the decimal point relative to the start of the string is