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HPUX Reference > Ddrand48(3C)HPUX 11i Version 3: February 2007 

NAMEdrand48(), erand48(), lrand48(), nrand48(), mrand48(), jrand48(), srand48(), seed48(), lcong48() — generate uniformly distributed pseudorandom 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]); Obsolescent Interfacesint drand48_r(struct drand48_data *dp, double *randval); int erand48_r( unsigned short int xsubi[3], struct drand48_data *dp, double *randval); int lrand48_r(struct drand48_data *dp, long int *randval); int nrand48_r( unsigned short int xsubi[3], struct drand48_data *dp, long int *randval); int mrand48_r(struct drand48_data *dp, long int *randval); int jrand48_r( unsigned short int xsubi[3], struct drand48_data *dp, long int *randval); int srand48_r(long int seedval, struct drand48_data *dp); int seed48_r(unsigned short int seed16v[3], struct drand48_data *dp); int lcong48_r(unsigned short int param[7], struct drand48_data *dp); DESCRIPTIONThis family of functions generates pseudorandom numbers using the wellknown linear congruential algorithm and 48bit integer arithmetic. In the following description, the formal mathematical notation [low,high) indicates an interval including low but not including high. drand48() and erand48() return nonnegative doubleprecision floatingpoint values uniformly distributed over the interval [0.0,1.0). lrand48() and nrand48() return nonnegative long integers uniformly distributed over the interval [0,2^31). mrand48() and jrand48() return signed long integers uniformly distributed over the interval [2^31,2^31). srand48(), seed48(), and lcong48() are initialization entry points, one of which should be invoked before either drand48(), lrand48(), or mrand48() is called. (Although it is not recommended practice, constant default initializer values are supplied automatically if drand48(), lrand48(), or mrand48() is called without a prior call to an initialization entry point.) erand48(), nrand48(), and jrand48() do not require an initialization entry point to be called first. All the routines work by generating a sequence of 48bit 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 48bit integer arithmetic is performed. Unless lcong48() 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 drand48(), erand48(), lrand48(), nrand48(), mrand48(), or jrand48() is computed by first generating the next 48bit 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 highorder (leftmost) bits of X[i] and transformed into the returned value. The functions drand48(), lrand48(), and mrand48() store the last 48bit X[i] generated in an internal buffer; that is why they must be initialized prior to being invoked. The functions erand48(), nrand48(), and jrand48() 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, erand48(), nrand48(), and jrand48() allow separate modules of a large program to generate several independent streams of pseudorandom 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 srand48() sets the highorder 32 bits of X[i] to the 32 bits contained in its argument. The loworder 16 bits of X[i] are set to the arbitrary value 0x330E (base 16). The initializer function seed48() sets the value of X[i] to the 48bit value specified in the argument array. In addition, the previous value of X[i] is copied into a 48bit internal buffer, used only by seed48(), and a pointer to this buffer is the value returned by seed48(). 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 seed48() when the program is restarted. The initialization function lcong48() allows the user to specify the initial X[i], the multiplier value a, and the addend value c. Argument array elements param[02] specify X[i], param[35] specify the multiplier a, and param[6] specifies the 16bit addend c. After lcong48() has been called, a subsequent call to either srand48() or seed48() restores the default multiplier and addend values for a and c, specified above. WARNINGSdrand48_r(), erand48_r(), lrand48_r(), nrand48_r(), mrand48_r(), jrand48_r(), srand48_r(), seed48_r() and lcong48_r() are obsolescent interfaces supported only for compatibility with existing DCE applications. New multithreaded applications should use drand48(), erand48(), lrand48(), nrand48(), mrand48(), jrand48(), srand48(), seed48(), and lcong48(). STANDARDS CONFORMANCEdrand48(): AES, SVID2, SVID3, XPG2, XPG3, XPG4 erand48(): AES, SVID2, SVID3, XPG2, XPG3, XPG4 jrand48(): AES, SVID2, SVID3, XPG2, XPG3, XPG4 lcong48(): AES, SVID2, SVID3, XPG2, XPG3, XPG4 lrand48(): AES, SVID2, SVID3, XPG2, XPG3, XPG4 mrand48(): AES, SVID2, SVID3, XPG2, XPG3, XPG4 nrand48(): AES, SVID2, SVID3, XPG2, XPG3, XPG4 seed48(): AES, SVID2, SVID3, XPG2, XPG3, XPG4 srand48(): AES, SVID2, SVID3, XPG2, XPG3, XPG4 
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