RAND48(3) BSD Library Functions Manual RAND48(3)

NAME
     ddrraanndd4488, eerraanndd4488, llrraanndd4488, nnrraanndd4488, mmrraanndd4488, jjrraanndd4488, ssrraanndd4488, sseeeedd4488,
     llccoonngg4488 - pseudo random number generators and initialization routines

LLIIBBRRAARRYY
     Standard C Library (libc, -lc)

SYNOPSIS
     ##iinncclluuddee <>

     double
     ddrraanndd4488(void);

     double
     eerraanndd4488(unsigned short xseed[3]);

     long
     llrraanndd4488(void);

     long
     nnrraanndd4488(unsigned short xseed[3]);

     long
     mmrraanndd4488(void);

     long
     jjrraanndd4488(unsigned short xseed[3]);

     void
     ssrraanndd4488(long seed);

     unsigned short *
     sseeeedd4488(unsigned short xseed[3]);

     void
     llccoonngg4488(unsigned short p[7]);

DESCRIPTION
     The rraanndd4488() family of functions generates pseudo-random numbers using a
     linear congruential algorithm working on integers 48 bits in size.  The
     particular formula employed is r(n+1) = (a * r(n) + c) mod m where the
     default values are for the multiplicand a = 0xfdeece66d = 25214903917 and
     the addend c = 0xb = 11.  The modulo is always fixed at m = 2 ** 48.
     r(n) is called the seed of the random number generator.

     For all the six generator routines described next, the first computa-
     tional step is to perform a single iteration of the algorithm.

     The ddrraanndd4488() and eerraanndd4488() functions return values of type double.  The
     full 48 bits of r(n+1) are loaded into the mantissa of the returned
     value, with the exponent set such that the values produced lie in the
     interval [0.0, 1.0).

     The llrraanndd4488() and nnrraanndd4488() functions return values of type long in the
     range [0, 2**31-1].  The high-order (31) bits of r(n+1) are loaded into
     the lower bits of the returned value, with the topmost (sign) bit set to
     zero.

     The mmrraanndd4488() and jjrraanndd4488() functions return values of type long in the
     range [-2**31, 2**31-1].  The high-order (32) bits of r(n+1) are loaded
     into the returned value.

     The ddrraanndd4488(), llrraanndd4488(), and mmrraanndd4488() functions use an internal buffer
     to store r(n).  For these functions the initial value of r(0) =
     0x1234abcd330e = 20017429951246.

     On the other hand, eerraanndd4488(), nnrraanndd4488(), and jjrraanndd4488() use a user-sup-
     plied buffer to store the seed r(n), which consists of an array of 3
     shorts, where the zeroth member holds the least significant bits.

     All functions share the same multiplicand and addend.

     The ssrraanndd4488() function is used to initialize the internal buffer r(n) of
     ddrraanndd4488(), llrraanndd4488(), and mmrraanndd4488() such that the 32 bits of the seed
     value are copied into the upper 32 bits of r(n), with the lower 16 bits
     of r(n) arbitrarily being set to 0x330e.  Additionally, the constant mul-
     tiplicand and addend of the algorithm are reset to the default values
     given above.

     The sseeeedd4488() function also initializes the internal buffer r(n) of
     ddrraanndd4488(), llrraanndd4488(), and mmrraanndd4488(), but here all 48 bits of the seed can
     be specified in an array of 3 shorts, where the zeroth member specifies
     the lowest bits.  Again, the constant multiplicand and addend of the
     algorithm are reset to the default values given above.  The sseeeedd4488()
     function returns a pointer to an array of 3 shorts which contains the old
     seed.  This array is statically allocated, thus its contents are lost
     after each new call to sseeeedd4488().

     Finally, llccoonngg4488() allows full control over the multiplicand and addend
     used in ddrraanndd4488(), eerraanndd4488(), llrraanndd4488(), nnrraanndd4488(), mmrraanndd4488(), and
     jjrraanndd4488(), and the seed used in ddrraanndd4488(), llrraanndd4488(), and mmrraanndd4488().  An
     array of 7 shorts is passed as argument; the first three shorts are used
     to initialize the seed; the second three are used to initialize the mul-
     tiplicand; and the last short is used to initialize the addend.  It is
     thus not possible to use values greater than 0xffff as the addend.

     Note that all three methods of seeding the random number generator always
     also set the multiplicand and addend for any of the six generator calls.

     For a more powerful random number generator, see random(3).

AUTHORS     Martin Birgmeier

SEE ALSO
     rand(3), random(3)

BSD                             October 8, 1993                            BSD