drand48(3C) drand48(3C)
NAME
drand48(), erand48(), lrand48(), nrand48(), mrand48(), jrand48(), srand48(), seed48(), lcong48() - generate uniformly distributed pseudo-
random numbers
SYNOPSIS
Obsolescent Interfaces
DESCRIPTION
This family of functions generates pseudo-random numbers using the well-known linear congruential algorithm and 48-bit integer arithmetic.
In the following description, the formal mathematical notation [low,high) indicates an interval including low but not including high.
and return nonnegative double-precision floating-point values uniformly distributed over the interval [0.0,1.0).
and return nonnegative long integers uniformly distributed over the interval [0,2^31).
and return signed long integers uniformly distributed over the interval [-2^31,2^31).
and are initialization entry points, one of which should be invoked before either or is called. (Although it is not recommended practice,
constant default initializer values are supplied automatically if or is called without a prior call to an initialization entry point.) and
do not require an initialization entry point to be called first.
All the routines work by generating a sequence of 48-bit integer values, X[i], according to the linear congruential formula
X[n+1] = (a*X[n] + c) modulo m n>=0
The parameter m = 2^48; hence 48-bit integer arithmetic is performed.
Unless has been invoked, the default multiplier value a and the default addend value c are given by
a = 0x5DEECE66D (base 16) = 0273673163155 (base 8)
c = 0xB (base 16) = 013 (base 8)
The value returned by any of the functions or is computed by first generating the next 48-bit X[i] in the sequence. Then the appropriate
number of bits, according to the type of data item to be returned, are copied from the high-order (leftmost) bits of X[i] and transformed
into the returned value.
The functions and store the last 48-bit X[i] generated in an internal buffer; that is why they must be initialized prior to being invoked.
The functions and require the calling program to provide storage for the successive X[i] values in the array specified as an argument when
the functions are invoked. That is why these routines do not have to be initialized; the calling program merely has to place the desired
initial value of X[i] into the array and pass it as an argument. By using different arguments, and allow separate modules of a large pro-
gram to generate several independent streams of pseudo-random numbers; i.e., the sequence of numbers in each stream do not depend upon how
many times the routines have been called to generate numbers for the other streams.
The initializer function sets the high-order 32 bits of X[i] to the 32 bits contained in its argument. The low-order 16 bits of X[i] are
set to the arbitrary value 0x330E (base 16).
The initializer function sets the value of X[i] to the 48-bit value specified in the argument array. In addition, the previous value of
X[i] is copied into a 48-bit internal buffer, used only by and a pointer to this buffer is the value returned by This returned pointer,
which can be ignored if not needed, is useful if a program is to be restarted from a given point at some future time; use the pointer to
get at and store the last X[i] value, and then use this value to reinitialize via when the program is restarted.
The initialization function allows the user to specify the initial X[i], the multiplier value a, and the addend value c. Argument array
elements param[0-2] specify X[i], param[3-5] specify the multiplier a, and param[6] specifies the 16-bit addend c. After has been called,
a subsequent call to either or restores the default multiplier and addend values for a and c, specified above.
Obsolescent Interfaces
generate uniformly distributed pseudo-random numbers.
WARNINGS
and are obsolescent interfaces supported only for compatibility with existing DCE applications. New multithreaded applications should use
and
SEE ALSO
rand(3C), random(3M), thread_safety(5), random(7).
STANDARDS CONFORMANCE
drand48(3C)