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--- a/parse/bitset.c

+++ b/parse/bitset.c

@@ -9,6 +9,13 @@

 #define Sizetbits (CHAR_BIT*sizeof(size_t)) /* used in graph reprs */

+/* Equalizes the size of a and b by

+ * growing the smaller to the size of the

+ * larger, zeroing out the new elements.

+ * This allows the code to simply iterate

+ * over both without keeping track of the

+ * minimum size.

+ */

 static void eqsz(Bitset *a, Bitset *b)

 {

     size_t sz;

@@ -35,6 +42,7 @@

     b->nchunks = sz;

 }

+/* Creates a new all-zero bit set */

 Bitset *mkbs()

 {

     Bitset *bs;

@@ -45,12 +53,16 @@

     return bs;

 }

+/* Frees a bitset. Safe to call on NULL. */

 void bsfree(Bitset *bs)

 {

+    if (!bs)

+        return;

     free(bs->chunks);

     free(bs);

 }

+/* Duplicates a bitset. NULL is duplicated to NULL. */

 Bitset *bsdup(Bitset *a)

 {

     Bitset *bs;

@@ -64,6 +76,7 @@

     return bs;

 }

+/* Zeroes all values in a bit set */

 Bitset *bsclear(Bitset *bs)

 {

     size_t i;

@@ -75,6 +88,7 @@

     return bs;

 }

+/* Counts the number of values held in a bit set */

 size_t bscount(Bitset *bs)

 {

     size_t i, j, n;

@@ -87,6 +101,23 @@

     return n;

 }

+/* A slightly tricky function to iterate over the contents

+ * of a bitset. It returns true immediately if 'elt' is in

+ * the bitset, otherwise it seeks forward to the next value

+ * held in the bitset and stores it in elt. If there are no

+ * more values, it returns false to stop iteration. Note,

+ * this means that you need to increment elt every time you

+ * pass through.

+ *

+ * Typical usage of this function:

+ *

+ *      for (i = 0; bsiter(set, &i); i++)

+ *          use(i);

+ *

+ * The increment of 'i' in the for loop is needed in order

+ * to prevent the function from returning the same value

+ * repeatedly.

+ */

 int bsiter(Bitset *bs, size_t *elt)

 {

     size_t i;

@@ -108,12 +139,6 @@

 size_t bsmax(Bitset *bs)

 {

     return bs->nchunks*Sizetbits;

-}

-

-void delbs(Bitset *bs)

-{

-    free(bs->chunks);

-    free(bs);

 }

 void bsput(Bitset *bs, size_t elt)