cuda double precision logarithm error

Question

I'm using C for CUDA on 3.0 computing capability and have to use built-in logarithm function of double precision. I found that for that purpose I should use double log(double x) function ( documentation ). But, if I pass a really small number within double precision scope (eg double x = 6.73E-42 ), log(x) function returns -Infinity . In Java Math.log() function for the same value returns -94.802 . Is this a bug within CUDA math library or am I getting something wrong?

EDIT: Here's the code I'm using in the kernel function

#include "math.h"
extern "C"
__global__ void smallLog(double* in, int n)
{
   int i = blockIdx.x * blockDim.x + threadIdx.x;
   if (i<n){
      double x = in[i];
      in[i] = log(x);
   }
}

Answer 1

Make sure you are compiling for compute capability 3.0 ( nvcc -arch sm_30 ).

By default, nvcc compiles for compute capability 1.0, which is single precision only and (as others have pointed out already) 6.73E-42 is zero in single precision and log(0) = -Infinity.

Answer 2

For your question, the answer should be -94.802.

Try splitting log(6.73E-42) into

log(6.731E-20) + log(1E-22) = [(-44.145)+(-50.66)]=(-94.802)

Or, if you want you can split into more pieces and finally add. Am sorry, my device doesn't support double-precision. That's the answer i can give.