## implementation of rand()

I am writing some embedded code in C and need to use the rand() function. Unfortunately, rand() is not supported in the library for the controller. I need a simple implementation that is fast, but more importantly has little space overhead, that produces relatively high-quality random numbers. Does anyone know which algorithm to use or sample code?

EDIT: It's for image processing, so "relatively high quality" means decent cycle length and good uniform properties.

Check out this collection of random number generators from George Marsaglia. He's a leading expert in random number generation, so I'd be confident using anything he recommends. The generators in that list are tiny, some requiring only a couple unsigned longs as state.

Marsaglia's generators are definitely "high quality" by your standards of long period and good uniform distribution. They pass stringent statistical tests, though they wouldn't do for cryptography.

**How does the rand() function in C work?,** \begingroup Given the typical implementation of rand() , you're using a quite generous definition of "works". IMO it does not work, even for non The rand function returns a pseudorandom integer in the range 0 to RAND_MAX (32767). Use the srand function to seed the pseudorandom-number generator before calling rand . Requirements

Use the C code for LFSR113 from L'écuyer:

unsigned int lfsr113_Bits (void) { static unsigned int z1 = 12345, z2 = 12345, z3 = 12345, z4 = 12345; unsigned int b; b = ((z1 << 6) ^ z1) >> 13; z1 = ((z1 & 4294967294U) << 18) ^ b; b = ((z2 << 2) ^ z2) >> 27; z2 = ((z2 & 4294967288U) << 2) ^ b; b = ((z3 << 13) ^ z3) >> 21; z3 = ((z3 & 4294967280U) << 7) ^ b; b = ((z4 << 3) ^ z4) >> 12; z4 = ((z4 & 4294967168U) << 13) ^ b; return (z1 ^ z2 ^ z3 ^ z4); }

Very high quality and fast. Do NOT use rand() for anything. It is worse than useless.

**rand() implementation,** the rand() facility is not a very good random number generator, because it is often poorly implemented. So I am planning to write my own What is the implementation of rand() on say visual c/c++ 5 or 6 ? Another question is this rand() implementation the same on any other platforms/compilers/libraries ? Where can I find/look at the implementation of rand() ? Thx for any help. Bye, Skybuck.

Here is a link to a ANSI C implementation of a few random number generators.

**rand() and srand() in C/C++,** create the same sequence again and again every time program runs. rand() function is used in C to generate random numbers. If we generate a sequence of random number with rand() function, it will create the same sequence again and again every time program runs.

**How does rand() work in C?,** (). These sequences are repeatable by calling srand() with the same seed value. The RAND Corporation is a research organization that develops solutions to public policy challenges to help make communities throughout the world safer and more secure, healthier and more prosperous. RAND is nonprofit, nonpartisan, and committed to the public interest.

I recommend the academic paper Two Fast Implementations of the Minimal Standard Random Number Generator by David Carta. You can find free PDF through Google. The original paper on the Minimal Standard Random Number Generator is also worth reading.

Carta's code gives fast, high-quality random numbers on 32-bit machines. For a more thorough evaluation, see the paper.

**C/Randomization,** rand() function is used in C to generate random numbers. If we generate a sequence of random number with rand() function, it will create the same class in C++ · Implementation of all Partition Allocation Methods in Memory Management The rand () function returns a pseudo-random integer in the range 0 to RAND_MAX inclusive (i.e., the mathematical range [0, RAND_MAX ]). The srand () function sets its argument as the seed for a new sequence of pseudo-random integers to be returned by rand (). These sequences are repeatable by calling srand () with the same seed value.

**What is the code for the rand() function which generates random ,** The C library function int rand(void) returns a pseudo-random number in the range of 0 to RAND_MAX. RAND_MAX is a constant whose default value may vary between implementations but it is granted to be at least 32767. printf("%d\n", rand() % 50); %50 is the range. $\begingroup$ I think the idea of the Standard is to make clear that code which intends to be portable shouldn't rely upon rand being anything better than that. From a conformance standpoint, I don't think the Standard would forbid an implementation which returned 42 for the first 5 calls after srand(8675309) nor one that would returned 42 for the first trillion calls regardless of the value

**srand(3): pseudo-random number generator,** The rand() function returns a pseudo-random integer in the range 0 to the following example of an implementation of rand() and srand(), possibly useful when RAND Corporation, in partnership with the American Institutes for Research, evaluated implementation of key elements of the Intensive Partnerships for Effective Teaching in three public school districts and four charter management organizations.

**std::rand,** It is implementation-defined which functions do so. It is implementation-defined whether rand() is thread-safe. Rand index adjusted for chance. The Rand Index computes a similarity measure between two clusterings by considering all pairs of samples and counting pairs that are assigned in the same or different clusters in the predicted and true clusterings.