# srand48(3) [ultrix man page]

drand48(3) Library Functions Manual drand48(3)Namedrand48, erand48, lrand48, nrand48, mrand48, jrand48, srand48, seed48, lcong48 - generate uniformly distributed pseudo-random numbersSyntaxdouble drand48 ( ) double erand48 (xsubi) unsigned short xsubi[3]; long lrand48 ( ) long nrand48 (xsubi) unsigned short xsubi[3]; long mrand48 ( ) long jrand48 (xsubi) unsigned short xsubi[3]; void srand48 (seedval) long seedval; unsigned short *seed48 (seed16v) unsigned short seed16v[3]; void lcong48 (param) unsigned short param[7];DescriptionNOTE: Your terminal may not be able to accurately display the special math symbols in this reference page. See the ULTRIX Programmer's Man- ual, Unsupported for a complete description of the math symbols. This family of functions generates pseudo-random numbers using the well-known linear congruential algorithm and 48-bit integer arithmetic. Functions and return non-negative double-precision floating-point values uniformly distributed over the interval [0.0, 1.0). Functions and return non-negative long integers uniformly distributed over the interval [0, 231). Functions and return signed long integers uniformly distributed over the interval [, 231). Functions 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 will be supplied automatically if or is called without a prior call to an initialization entry point. Functions 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, Xi, according to the linear congruential formula Xn+1 = (aXn+c)mod m n>=0. The parameter m=248; hence 48-bit integer arithmetic is performed. Unless has been invoked, the multiplier value a and the addend value c are given by a = 5DEECE66D16 = 2736731631558 c = B16 = 138. The value returned by any of the functions or 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, are copied from the high-order (leftmost) bits of Xi and transformed into the returned value. The functions and store the last 48-bit Xi 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 Xi 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 Xi into the array and pass it as an argument. By using different arguments, functions and allow separate modules of a large program to generate several independent streams of pseudo-random numbers. That is, the sequence of numbers in each stream will 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 Xi to the 32 bits contained in its argument. The low-order 16 bits of Xi are set to the arbitrary value 330E16. The initializer function sets the value of Xi to the 48-bit value specified in the argument array. In addition, the previous value of Xi 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 just be ignored if not needed, is useful if a program is to be restarted from a given point at some future time-231use the pointer to get at and store the last Xi value, and then use this value to reinitialize via when the program is restarted. The initialization function allows the user to specify the initial Xi, the multiplier value a, and the addend value c. Argument array ele- ments param[0-2] specify Xi, param[3-5] specify the multiplier a, and param[6] specifies the 16-bit addend c. After has been called, a sub- sequent call to either or will restore the ``standard'' multiplier and addend values, a and c, specified on the previous page.--NotesThe source code for the portable version can even be used on computers which do not have floating-point arithmetic. In such a situation, functions and do not exist. Instead, they are replaced by the two new functions below. long irand48 (m) unsigned short m; long krand48 (xsubi, m) unsigned short xsubi[3], m; Functions and return non-negative long integers uniformly distributed over the interval [0, m-1].See Alsorand(3) ULTRIX Programmer's Manual, Unsupported drand48(3)