Hello,
 
I added 2 functions to the "randist" module (modified files: gsl_randist.h, gauss.c) which compute
 
1) P(X <=x) <--> double gsl_ran_ugaussian_cuml_inf (const double x)
2) P(X >=x) <--> double gsl_ran_ugaussian_cuml_sup (const double x)
 
--
Fabrice Lebel