diff --git a/src/CUDA/NVRTCKernels/CudaChiSquareKernel.cu b/src/CUDA/NVRTCKernels/CudaChiSquareKernel.cu
index b22cab7..9a7f808 100644
--- a/src/CUDA/NVRTCKernels/CudaChiSquareKernel.cu
+++ b/src/CUDA/NVRTCKernels/CudaChiSquareKernel.cu
@@ -83,6 +83,56 @@ __device__ double ifld(double t, double alpha, double phi, double nu, double lam
   return alpha*cos(wt+ph)*exp(-lambdaT*t) + (1.0-alpha)*exp(-lambdaL*t);
 }
 
+__device__ double ifgk(double t, double alpha, double nu, double sigma, double lambda, double beta) {
+  double wt = TWO_PI*nu*t;
+  double rate2 = sigma*sigma*t*t;
+  double rateL = 0.0;
+  double result = 0.0;
+
+  // make sure lambda > 0
+  if (lambda < 0.0)
+    return 0.0;
+
+  if (beta < 0.001) {
+    rateL = 1.0;
+  } else {
+    rateL = pow(lambda*t, beta);
+  }
+
+  if (nu < 0.01) {
+    result = (1.0-alpha)*exp(-rateL) + alpha*(1.0-rate2)*exp(-0.5*rate2);
+  } else {
+    result = (1.0-alpha)*exp(-rateL) + alpha*(cos(wt)-sigma*sigma*t*t/(wt)*sin(wt))*exp(-0.5*rate2);
+  }
+
+  return result;
+}
+
+__device__ double ifll(double t, double alpha, double nu, double a, double lambda, double beta) {
+  double wt = TWO_PI*nu*t;
+  double at = a*t;
+  double rateL = 0.0;
+  double result = 0.0;
+
+  // make sure lambda > 0
+  if (lambda < 0.0)
+    return 0.0;
+
+  if (beta < 0.001) {
+    rateL = 1.0;
+  } else {
+    rateL = pow(lambda*t, beta);
+  }
+
+  if (nu < 0.01) {
+    result = (1.0-alpha)*exp(-rateL) + alpha*(1.0-at)*exp(-at);
+  } else {
+    result = (1.0-alpha)*exp(-rateL) + alpha*(cos(wt)-a/(TWO_PI*nu)*sin(wt))*exp(-at);
+  }
+
+  return result;
+}
+
 __device__ double b(double t, double phi, double nu) {
   return j0(TWO_PI*nu*t + DEG_TO_RAD*phi);
 }
diff --git a/src/OpenCL/OpenCLKernels/OpenCLChiSquareRuntime.cl b/src/OpenCL/OpenCLKernels/OpenCLChiSquareRuntime.cl
index bdc9374..73ddaa4 100644
--- a/src/OpenCL/OpenCLKernels/OpenCLChiSquareRuntime.cl
+++ b/src/OpenCL/OpenCLKernels/OpenCLChiSquareRuntime.cl
@@ -106,6 +106,56 @@ double ifld(double t, double alpha, double phi, double nu, double lambdaT, doubl
   return alpha*cos(wt+ph)*exp(-lambdaT*t) + (1.0-alpha)*exp(-lambdaL*t);
 }
 
+double ifgk(double t, double alpha, double nu, double sigma, double lambda, double beta) {
+  double wt = TWO_PI*nu*t;
+  double rate2 = sigma*sigma*t*t;
+  double rateL = 0.0;
+  double result = 0.0;
+
+  // make sure lambda > 0
+  if (lambda < 0.0)
+    return 0.0;
+
+  if (beta < 0.001) {
+    rateL = 1.0;
+  } else {
+    rateL = pow(lambda*t, beta);
+  }
+
+  if (nu < 0.01) {
+    result = (1.0-alpha)*exp(-rateL) + alpha*(1.0-rate2)*exp(-0.5*rate2);
+  } else {
+    result = (1.0-alpha)*exp(-rateL) + alpha*(cos(wt)-sigma*sigma*t*t/(wt)*sin(wt))*exp(-0.5*rate2);
+  }
+
+  return result;
+}
+
+double ifll(double t, double alpha, double nu, double a, double lambda, double beta) {
+  double wt = TWO_PI*nu*t;
+  double at = a*t;
+  double rateL = 0.0;
+  double result = 0.0;
+
+  // make sure lambda > 0
+  if (lambda < 0.0)
+    return 0.0;
+
+  if (beta < 0.001) {
+    rateL = 1.0;
+  } else {
+    rateL = pow(lambda*t, beta);
+  }
+
+  if (nu < 0.01) {
+    result = (1.0-alpha)*exp(-rateL) + alpha*(1.0-at)*exp(-at);
+  } else {
+    result = (1.0-alpha)*exp(-rateL) + alpha*(cos(wt)-a/(TWO_PI*nu)*sin(wt))*exp(-at);
+  }
+
+  return result;
+}
+
 double b(double t, double phi, double nu) {
   return bessj0(TWO_PI*nu*t + DEG_TO_RAD*phi);
 }