Added better comments

bin_dfs.c

 #include <inttypes.h> // uint64_t
-#include <stdio.h>
-#include <stdlib.h>
 #include "bin_dfs.h"
 
 // private helper functions
@@ -25,6 +23,8 @@ long double cdf(uint64_t k, uint64_t n, long double p){
 }
 
 
+// Can't do tail recursion here because the intermediate products can get
+// far larger than LDBL_MAX
 long double pmf_helper(uint64_t k, uint64_t n, long double p){
 	// work through our k's then work through our n's.
 	if(n == 0)

bin_dfs.h

@@ -19,11 +19,12 @@ long double pmf(uint64_t k, uint64_t n, long double p);
  * Purpose:
  * 	 Recusively sum up the probabilities for each i<=n
  * Assumptions:
- * 	 i<=n
+ * 	 k <= n
  * Returns:
- * 	 P(X<=i) where X~bin(n, p)
+ * 	 P(X<=k) where X~bin(n, p)
+ * 	 ie, \sum_{j=0}^k pmf(j, n, p)
  */
-long double cdf(uint64_t i, uint64_t n, long double p);
+long double cdf(uint64_t k, uint64_t n, long double p);
 
 #endif // DIST_FUNCT_H