Even better documentation of filters.

filter/Doc

@@ -1,3 +1,3 @@
 H Filters
 S filter.c
-S tree.c
+S tree.c

filter/filter.c

@@ -25,7 +25,7 @@
  *
  * Filters use structure &f_val for its variables. Each &f_val
  * contains type and value. Types are constants prefixed with %T_. Few
- * of types are special; %T_RETURN can be or-ed with type to indicate
+ * of types are special; %T_RETURN can be or--ed with type to indicate
  * that return from function/from whole filter should be
  * forced. Important thing about &f_val s is that they may be copied
  * with simple =. That's fine for all currently defined types: strings
@@ -71,8 +71,14 @@ pm_path_compare(struct f_path_mask *m1, struct f_path_mask *m2)
   }
 }
 
-/*
+/**
- * val_compare - compare two values, returns -1, 0, 1 on <, =, > and 999 on error
+ * val_compare
+ * @v1: first value
+ * @v2: second value
+ *
+ * Compares two values and returns -1, 0, 1 on <, =, > or 999 on error.
+ * Tree module relies on this giving consistent results so that it can
+ * build balanced trees.
  */
 int
 val_compare(struct f_val v1, struct f_val v2)
@@ -140,8 +146,13 @@ val_simple_in_range(struct f_val v1, struct f_val v2)
   return CMP_ERROR;
 }
 
-/*
+/**
- * val_in_range - check if @v1 ~ @v2
+ * val_in_range
+ * @v1: element
+ * @v2: set
+ *
+ * Checks if @v1 is element (|~| operator) of @v2. Sets are internally represented as balanced trees, see
+ * tree.c module (this is not limited to sets, but for non-set cases, val_simple_in_range() is called early).
  */
 int
 val_in_range(struct f_val v1, struct f_val v2)

filter/tree.c

@@ -11,7 +11,7 @@
 #include "filter/filter.h"
 
 /*
- * find_nth - finds n-th element in linked list. Don't be confused by tree structures.
+ * find_nth - finds n-th element in linked list. Don't be confused by types, it is really a linked list.
  */
 static struct f_tree *
 find_nth(struct f_tree *from, int nth)
@@ -44,7 +44,7 @@ find_nth(struct f_tree *from, int nth)
 }
 
 /*
- * find_median - Gets list linked by left, finds its median, trashes pointers in right
+ * find_median - Gets list linked by @left, finds its median, trashes pointers in @right.
  */
 static struct f_tree *
 find_median(struct f_tree *from)
@@ -69,6 +69,9 @@ find_median(struct f_tree *from)
  * Search for given value in the tree. I relies on fact that sorted tree is populated
  * by &f_val structures (that can be compared by val_compare()). In each node of tree, 
  * either single value (then t->from==t->to) or range is present.
+ *
+ * Both set matching and switch() { } construction is implemented using this function,
+ * thus both are as fast as they can be.
  */
 struct f_tree *
 find_tree(struct f_tree *t, struct f_val val)
@@ -86,7 +89,7 @@ find_tree(struct f_tree *t, struct f_val val)
 
 /**
  * build_tree
- * @from: degenerated tree (linked by tree->left) to be transformed into form suitable for find_tree()
+ * @from: degenerated tree (linked by @tree->left) to be transformed into form suitable for find_tree()
  *
  * Transforms denerated tree into balanced tree.
  */
@@ -130,6 +133,13 @@ f_new_tree(void)
   return ret;
 }
 
+/**
+ * same_tree
+ * @t1: first tree to be compared
+ * @t2: second one
+ *
+ * Compares two trees and returns 1 if they are same
+ */
 int
 same_tree(struct f_tree *t1, struct f_tree *t2)
 {