Generates uniformly distributed pseudorandom number sequences. Returns 48-bit, nonnegative, double-precision floating-point values.
#include <stdlib.h> double drand48 (void);
It returns non-negative, double-precision, floating-point values uniformly distributed over the range of y values such that 0.0 1.0.
Before you call drand48, use either srand48, seed48, or lcong48 to initialize the random number generator. You must initalize prior to invoking the drand48 function because it stores the last 48-bit Xi generated into an internal buffer. (Although it is not recommended, constant default initializer values are supplied automatically if the drand48, lrand48, or mrand48 functions are called without first calling an initialization function.)
The drand48 function works 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 argument m equals 248 , so 48-bit integer arithmetic is performed. Unless you invoke lcong48, the multiplier value a and the addend value c are:
a = 5DEECE66D16 = 2736731631558
c = B16 = 138
The values returned by drand48 are computed by first generating the next 48-bit Xi in the sequence. Then the appropriate bits, according to the type of returned data item, are copied from the high-order (most significant) bits of Xi and transformed into the returned value.
See also srand48, seed48, lcong48, lrand48, and mrand48 in this section.
| n | A nonnegative, double-precision, floating-point value. |