curand generator fails on odd number of elements

Question

I tried the following program which uses curand to generate random numbers. When the number of elements to generate (variable n) is an odd number like 9849 below, I got an error on the line with curandGenerateNormal. Even number of elements does not have this problem. What is the reason of that?

#include <curand.h>
#include <iostream>
#include <cstdlib>
using namespace std;

#define CHKcuda(x) do {                             \
  cudaError_t y = (x);                              \
  if (y != cudaSuccess) {                           \
    cout << __LINE__ << ": " << y << endl; exit(1); \
  }                                                 \
} while(0)
#define CHKcurand(x) do {                           \
  curandStatus_t y = (x);                           \
  if (y != CURAND_STATUS_SUCCESS) {                 \
    cout << __LINE__ << ": " << y << endl; exit(1); \
  }                                                 \
} while(0)

int main(int argc, char** argv) {
  curandGenerator_t g_randgen;
  float *ptr, *h_ptr;
  int n;
  if (argc > 1) {
    n = atoi(argv[1]);
  }  
  CHKcurand(curandCreateGenerator(&g_randgen, CURAND_RNG_PSEUDO_DEFAULT));
  CHKcuda(cudaMalloc((void**)&ptr, n * sizeof(float)));
  CHKcurand(curandGenerateNormal(g_randgen, ptr, n, 0, 0.1));
  h_ptr = static_cast<float*>(malloc(sizeof(float) * n));
  CHKcuda(cudaMemcpy(h_ptr, ptr, sizeof(float) * n, cudaMemcpyDeviceToHost));
  CHKcuda(cudaDeviceSynchronize());
  for (int i = 0; i < 5; i++) {
    cout << h_ptr[i] << ", ";
  }
  cout << endl;
  return 0;
}

EDIT:

I checked the return value of the generating function. The definition of the error code says the following:

CURAND_STATUS_LENGTH_NOT_MULTIPLE = 105, ///< Length requested is not a multple of dimension

However, in the documentation it only says when generating quasirandom numbers, the number of elements must be a multiple of the dimension. So why it affects the pseudorandom number generation here? Or is the parameter I'm using to create the generator (CURAND_RNG_PSEUDO_DEFAULT) actually created a quasirandom number generator? And moreover, what is the exact value of the dimension and where can I find it out?

Robert Crovella · Accepted Answer · 2014-02-04T21:20:23.257

In general, the normal generating functions (e.g. curandGenerateNormal, curandGenerateLogNormal, etc.) require the number of requested points to be a multiple of 2, for a pseudorandom RNG.

This is documented:

curandStatus_t CURANDAPI curandGenerateNormal ( curandGenerator_t generator, float* outputPtr, size_t n, float  mean, float  stddev ) 

Generate normally distributed doubles. 


Parameters 
generator- Generator to use outputPtr- Pointer to device memory to store CUDA-generated results, or Pointer to host memory to store CPU-generated results n- Number of floats to generate mean- Mean of normal distribution stddev- Standard deviation of normal distribution

Returns


•CURAND_STATUS_NOT_INITIALIZED if the generator was never created 
•CURAND_STATUS_PREEXISTING_FAILURE if there was an existing error from a previous kernel launch 
•CURAND_STATUS_LAUNCH_FAILURE if the kernel launch failed for any reason 
•CURAND_STATUS_LENGTH_NOT_MULTIPLE if the number of output samples is not a multiple of the quasirandom dimension, or is not a multiple of two for pseudorandom generators 
•CURAND_STATUS_SUCCESS if the results were generated successfully

curandGenerateUniform, for example, does not have this restriction.

It looks like some cuRAND host random number generators read past the end of internally allocated memory if the number of output samples is not a multiple of four, but I currently don't have time to investigate further. — tera, Nov 28 '19 at 14:21

curand generator fails on odd number of elements

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