drand48, erand48, lrand48, nrand48, mrand48, jrand48,
srand48, seed48, lcong48 - generate uniformly distributed
double erand48(unsigned short int xsubi);
long int lrand48(void);
long int nrand48(unsigned short int xsubi);
long int mrand48(void);
long int jrand48(unsigned short int xsubi);
void srand48(long int seedval);
unsigned short int *seed48(unsignedshortint seed16v );
void lcong48(unsigned short int param);
These functions generate pseudo-random numbers using the
linear congruential algorithm and 48-bit integer arith
The drand48() and erand48() functions return non-negative
double-precision floating-point values uniformly dis
tributed 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 ini
tialization functions, one of which should be called
before using drand48(), lrand48() or mrand49(). The func
tions 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 for
Xn+1 = (aXn + c) mod m, where n >= 0
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
The functions drand48(), lrand48() and mrand48() store the
last 48-bit Xi generated in an internal buffer. The func
tions erand48(), nrand48() and jrand48() require the call
ing program to provide storage for the successive Xi val
ues in the array argument xsubi. The functions are ini
tialized 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 specifies c. After lcong48() has been called, a
subsequent call to either srand48() or seed48() will
restore the standard values of a and c.
These functions are declared obsolete by SVID 3, which
states that rand(3) should be used instead.