Author: ed
Date: Thu Oct 13 18:25:40 2016
New Revision: 307227
URL: https://svnweb.freebsd.org/changeset/base/307227

Log:
  Improve typing of POSIX search tree functions.
  
  Back in 2015 when I reimplemented these functions to use an AVL tree, I
  was annoyed by the weakness of the typing of these functions. Both tree
  nodes and keys are represented by 'void *', meaning that things like the
  documentation for these functions are an absolute train wreck.
  
  To make things worse, users of these functions need to cast the return
  value of tfind()/tsearch() from 'void *' to 'type_of_key **' in order to
  access the key. Technically speaking such casts violate aliasing rules.
  I've observed actual breakages as a result of this by enabling features
  like LTO.
  
  I've filed a bug report at the Austin Group. Looking at the way the bug
  got resolved, they made a pretty good step in the right direction. A new
  type 'posix_tnode' has been added to correspond to tree nodes. It is
  still defined as 'void' for source-level compatibility, but in the very
  far future it could be replaced by a proper structure type containing a
  key pointer.
  
  MFC after:    1 month
  Differential Revision:        https://reviews.freebsd.org/D8205

Modified:
  head/include/search.h
  head/lib/libc/stdlib/tdelete.c
  head/lib/libc/stdlib/tfind.c
  head/lib/libc/stdlib/tsearch.3
  head/lib/libc/stdlib/tsearch.c
  head/lib/libc/stdlib/twalk.c
  head/lib/libc/tests/stdlib/tsearch_test.c

Modified: head/include/search.h
==============================================================================
--- head/include/search.h       Thu Oct 13 18:02:29 2016        (r307226)
+++ head/include/search.h       Thu Oct 13 18:25:40 2016        (r307227)
@@ -34,16 +34,18 @@ typedef     enum {
 } VISIT;
 
 #ifdef _SEARCH_PRIVATE
-typedef        struct node {
-       void         *key;
-       struct node  *llink, *rlink;
-       signed char   balance;
-} node_t;
+typedef struct __posix_tnode {
+       void                    *key;
+       struct __posix_tnode    *llink, *rlink;
+       signed char              balance;
+} posix_tnode;
 
 struct que_elem {
        struct que_elem *next;
        struct que_elem *prev;
 };
+#else
+typedef void posix_tnode;
 #endif
 
 #if __BSD_VISIBLE
@@ -62,12 +64,15 @@ void        *lfind(const void *, const void *, 
 void   *lsearch(const void *, void *, size_t *, size_t,
            int (*)(const void *, const void *));
 void    remque(void *);
-void   *tdelete(const void * __restrict, void ** __restrict,
+void   *tdelete(const void * __restrict, posix_tnode ** __restrict,
            int (*)(const void *, const void *));
-void   *tfind(const void *, void * const *,
+posix_tnode *
+        tfind(const void *, posix_tnode * const *,
            int (*)(const void *, const void *));
-void   *tsearch(const void *, void **, int (*)(const void *, const void *));
-void    twalk(const void *, void (*)(const void *, VISIT, int));
+posix_tnode *
+        tsearch(const void *, posix_tnode **,
+           int (*)(const void *, const void *));
+void    twalk(const posix_tnode *, void (*)(const posix_tnode *, VISIT, int));
 
 #if __BSD_VISIBLE
 int     hcreate_r(size_t, struct hsearch_data *);

Modified: head/lib/libc/stdlib/tdelete.c
==============================================================================
--- head/lib/libc/stdlib/tdelete.c      Thu Oct 13 18:02:29 2016        
(r307226)
+++ head/lib/libc/stdlib/tdelete.c      Thu Oct 13 18:25:40 2016        
(r307227)
@@ -46,9 +46,9 @@ __FBSDID("$FreeBSD$");
                 * that we won't need to perform any rotations above    \
                 * this point. In this case rotations are always        \
                 * capable of keeping the subtree in balance. Make      \
-                * this the base node and reset the path.               \
+                * this the root node and reset the path.               \
                 */                                                     \
-               base = leaf;                                            \
+               rootp = leaf;                                           \
                path_init(&path);                                       \
        }                                                               \
        path_taking_left(&path);                                        \
@@ -59,7 +59,7 @@ __FBSDID("$FreeBSD$");
 #define        GO_RIGHT() do {                                                 
\
        if ((*leaf)->balance == 0 ||                                    \
            ((*leaf)->balance > 0 && (*leaf)->llink->balance == 0)) {   \
-               base = leaf;                                            \
+               rootp = leaf;                                           \
                path_init(&path);                                       \
        }                                                               \
        path_taking_right(&path);                                       \
@@ -67,18 +67,16 @@ __FBSDID("$FreeBSD$");
 } while (0)
 
 void *
-tdelete(const void *restrict key, void **restrict rootp,
+tdelete(const void *restrict key, posix_tnode **restrict rootp,
     int (*compar)(const void *, const void *))
 {
        struct path path;
-       node_t *root, **base, **leaf, *old, **n, *x, *y, *z;
-       void *result;
+       posix_tnode **leaf, *old, **n, *x, *y, *z, *result;
        int cmp;
 
        /* POSIX requires that tdelete() returns NULL if rootp is NULL. */
        if (rootp == NULL)
                return (NULL);
-       root = *rootp;
 
        /*
         * Find the leaf that needs to be removed. Return if we cannot
@@ -86,19 +84,18 @@ tdelete(const void *restrict key, void *
         * to get to the node, as we will need it to adjust the
         * balances.
         */
-       result = (void *)1;
+       result = (posix_tnode *)1;
        path_init(&path);
-       base = &root;
-       leaf = &root;
+       leaf = rootp;
        for (;;) {
                if (*leaf == NULL)
                        return (NULL);
                cmp = compar(key, (*leaf)->key);
                if (cmp < 0) {
-                       result = &(*leaf)->key;
+                       result = *leaf;
                        GO_LEFT();
                } else if (cmp > 0) {
-                       result = &(*leaf)->key;
+                       result = *leaf;
                        GO_RIGHT();
                } else {
                        break;
@@ -134,7 +131,7 @@ tdelete(const void *restrict key, void *
         * and left-left case that only exists when deleting. Hence the
         * duplication of code.
         */
-       for (n = base; n != leaf;) {
+       for (n = rootp; n != leaf;) {
                if (path_took_left(&path)) {
                        x = *n;
                        if (x->balance < 0) {
@@ -207,6 +204,5 @@ tdelete(const void *restrict key, void *
        }
 
        /* Return the parent of the old entry. */
-       *rootp = root;
        return (result);
 }

Modified: head/lib/libc/stdlib/tfind.c
==============================================================================
--- head/lib/libc/stdlib/tfind.c        Thu Oct 13 18:02:29 2016        
(r307226)
+++ head/lib/libc/stdlib/tfind.c        Thu Oct 13 18:25:40 2016        
(r307227)
@@ -4,8 +4,6 @@
  * Tree search generalized from Knuth (6.2.2) Algorithm T just like
  * the AT&T man page says.
  *
- * The node_t structure is for internal use only, lint doesn't grok it.
- *
  * Written by reading the System V Interface Definition, not the code.
  *
  * Totally public domain.
@@ -29,11 +27,10 @@ __FBSDID("$FreeBSD$");
  * vkey   - key to be found 
  * vrootp - address of the tree root 
  */
-void *
-tfind(const void *vkey, void * const *vrootp,
+posix_tnode *
+tfind(const void *vkey, posix_tnode * const *rootp,
     int (*compar)(const void *, const void *))
 {
-       node_t **rootp = (node_t **)vrootp;
 
        if (rootp == NULL)
                return NULL;

Modified: head/lib/libc/stdlib/tsearch.3
==============================================================================
--- head/lib/libc/stdlib/tsearch.3      Thu Oct 13 18:02:29 2016        
(r307226)
+++ head/lib/libc/stdlib/tsearch.3      Thu Oct 13 18:25:40 2016        
(r307227)
@@ -27,7 +27,7 @@
 .\"    OpenBSD: tsearch.3,v 1.2 1998/06/21 22:13:49 millert Exp
 .\" $FreeBSD$
 .\"
-.Dd December 6, 2015
+.Dd October 9, 2016
 .Dt TSEARCH 3
 .Os
 .Sh NAME
@@ -36,13 +36,13 @@
 .Sh SYNOPSIS
 .In search.h
 .Ft void *
-.Fn tdelete "const void * restrict key" "void ** restrict rootp" "int 
(*compar) (const void *, const void *)"
-.Ft void *
-.Fn tfind "const void *key" "void * const *rootp" "int (*compar) (const void 
*, const void *)"
-.Ft void *
-.Fn tsearch "const void *key" "void **rootp" "int (*compar) (const void *, 
const void *)"
+.Fn tdelete "const void * restrict key" "posix_tnode ** restrict rootp" "int 
(*compar) (const void *, const void *)"
+.Ft posix_tnode *
+.Fn tfind "const void *key" "posix_tnode * const *rootp" "int (*compar) (const 
void *, const void *)"
+.Ft posix_tnode *
+.Fn tsearch "const void *key" "posix_tnode **rootp" "int (*compar) (const void 
*, const void *)"
 .Ft void
-.Fn twalk "const void *root" "void (*action) (const void *, VISIT, int)"
+.Fn twalk "const posix_tnode *root" "void (*action) (const posix_tnode *, 
VISIT, int)"
 .Sh DESCRIPTION
 The
 .Fn tdelete ,
@@ -134,3 +134,18 @@ function returns no value.
 .Xr bsearch 3 ,
 .Xr hsearch 3 ,
 .Xr lsearch 3
+.Sh STANDARDS
+These functions conform to
+.St -p1003.1-2008 .
+.Pp
+The
+.Fa posix_tnode
+type is not part of
+.St -p1003.1-2008 ,
+but it is expected to be standardized by future versions of the standard.
+It is defined as
+.Fa void
+for source-level compatibility.
+Using
+.Fa posix_tnode
+makes it easier to distinguish between nodes and keys.

Modified: head/lib/libc/stdlib/tsearch.c
==============================================================================
--- head/lib/libc/stdlib/tsearch.c      Thu Oct 13 18:02:29 2016        
(r307226)
+++ head/lib/libc/stdlib/tsearch.c      Thu Oct 13 18:25:40 2016        
(r307227)
@@ -32,18 +32,17 @@ __FBSDID("$FreeBSD$");
 
 #include "tsearch_path.h"
 
-void *
-tsearch(const void *key, void **rootp,
+posix_tnode *
+tsearch(const void *key, posix_tnode **rootp,
     int (*compar)(const void *, const void *))
 {
        struct path path;
-       node_t *root, **base, **leaf, *result, *n, *x, *y, *z;
+       posix_tnode **leaf, *result, *n, *x, *y, *z;
        int cmp;
 
        /* POSIX requires that tsearch() returns NULL if rootp is NULL. */
        if (rootp == NULL)
-       return (NULL);
-               root = *rootp;
+               return (NULL);
 
        /*
         * Find the leaf where the new key needs to be inserted. Return
@@ -52,8 +51,7 @@ tsearch(const void *key, void **rootp,
         * balances.
        */
        path_init(&path);
-       base = &root;
-       leaf = &root;
+       leaf = rootp;
        while (*leaf != NULL) {
                if ((*leaf)->balance != 0) {
                        /*
@@ -62,9 +60,9 @@ tsearch(const void *key, void **rootp,
                         * need to perform any rotations above this
                         * point. In this case rotations are always
                         * capable of keeping the subtree in balance.
-                        * Make this the base node and reset the path.
+                        * Make this the root node and reset the path.
                         */
-                       base = leaf;
+                       rootp = leaf;
                        path_init(&path);
                }
                cmp = compar(key, (*leaf)->key);
@@ -75,7 +73,7 @@ tsearch(const void *key, void **rootp,
                        path_taking_right(&path);
                        leaf = &(*leaf)->rlink;
                } else {
-                       return (&(*leaf)->key);
+                       return (*leaf);
                }
        }
 
@@ -94,7 +92,7 @@ tsearch(const void *key, void **rootp,
         * have a balance of zero, meaning that these nodes will not get
         * out of balance.
        */
-       for (n = *base; n != *leaf;) {
+       for (n = *rootp; n != *leaf;) {
                if (path_took_left(&path)) {
                        n->balance += 1;
                        n = n->llink;
@@ -106,10 +104,10 @@ tsearch(const void *key, void **rootp,
 
        /*
         * Adjusting the balances may have pushed the balance of the
-        * base node out of range. Perform a rotation to bring the
+        * root node out of range. Perform a rotation to bring the
         * balance back in range.
         */
-       x = *base;
+       x = *rootp;
        if (x->balance > 1) {
                y = x->llink;
                if (y->balance < 0) {
@@ -129,7 +127,7 @@ tsearch(const void *key, void **rootp,
                        z->llink = y;
                        x->llink = z->rlink;
                        z->rlink = x;
-                       *base = z;
+                       *rootp = z;
 
                        x->balance = z->balance > 0 ? -1 : 0;
                        y->balance = z->balance < 0 ? 1 : 0;
@@ -146,7 +144,7 @@ tsearch(const void *key, void **rootp,
                         */
                        x->llink = y->rlink;
                        y->rlink = x;
-                       *base = y;
+                       *rootp = y;
 
                        x->balance = 0;
                        y->balance = 0;
@@ -165,12 +163,12 @@ tsearch(const void *key, void **rootp,
                         *      / \          A B   C D
                         *     B   C
                         */
-                       node_t *z = y->llink;
+                       posix_tnode *z = y->llink;
                        x->rlink = z->llink;
                        z->llink = x;
                        y->llink = z->rlink;
                        z->rlink = y;
-                       *base = z;
+                       *rootp = z;
 
                        x->balance = z->balance < 0 ? 1 : 0;
                        y->balance = z->balance > 0 ? -1 : 0;
@@ -187,7 +185,7 @@ tsearch(const void *key, void **rootp,
                         */
                        x->rlink = y->llink;
                        y->llink = x;
-                       *base = y;
+                       *rootp = y;
 
                        x->balance = 0;
                        y->balance = 0;
@@ -195,6 +193,5 @@ tsearch(const void *key, void **rootp,
        }
 
        /* Return the new entry. */
-       *rootp = root;
-       return (&result->key);
+       return (result);
 }

Modified: head/lib/libc/stdlib/twalk.c
==============================================================================
--- head/lib/libc/stdlib/twalk.c        Thu Oct 13 18:02:29 2016        
(r307226)
+++ head/lib/libc/stdlib/twalk.c        Thu Oct 13 18:25:40 2016        
(r307227)
@@ -4,8 +4,6 @@
  * Tree search generalized from Knuth (6.2.2) Algorithm T just like
  * the AT&T man page says.
  *
- * The node_t structure is for internal use only, lint doesn't grok it.
- *
  * Written by reading the System V Interface Definition, not the code.
  *
  * Totally public domain.
@@ -23,12 +21,11 @@ __FBSDID("$FreeBSD$");
 #include <search.h>
 #include <stdlib.h>
 
-typedef void (*cmp_fn_t)(const void *, VISIT, int);
+typedef void (*cmp_fn_t)(const posix_tnode *, VISIT, int);
 
 /* Walk the nodes of a tree */
 static void
-trecurse(const node_t *root,   /* Root of the tree to be walked */
-       cmp_fn_t action, int level)
+trecurse(const posix_tnode *root, cmp_fn_t action, int level)
 {
 
        if (root->llink == NULL && root->rlink == NULL)
@@ -46,7 +43,7 @@ trecurse(const node_t *root,  /* Root of 
 
 /* Walk the nodes of a tree */
 void
-twalk(const void *vroot, cmp_fn_t action) /* Root of the tree to be walked */
+twalk(const posix_tnode *vroot, cmp_fn_t action)
 {
        if (vroot != NULL && action != NULL)
                trecurse(vroot, action, 0);

Modified: head/lib/libc/tests/stdlib/tsearch_test.c
==============================================================================
--- head/lib/libc/tests/stdlib/tsearch_test.c   Thu Oct 13 18:02:29 2016        
(r307226)
+++ head/lib/libc/tests/stdlib/tsearch_test.c   Thu Oct 13 18:25:40 2016        
(r307227)
@@ -34,7 +34,7 @@ __FBSDID("$FreeBSD$");
 
 /* Validates the integrity of an AVL tree. */
 static inline unsigned int
-tnode_assert(const node_t *n)
+tnode_assert(const posix_tnode *n)
 {
        unsigned int height_left, height_right;
        int balance;
@@ -79,7 +79,7 @@ ATF_TC_BODY(tsearch_test, tc)
                keys[i] = i;
 
        /* Apply random operations on a binary tree and check the results. */
-       void *root = NULL;
+       posix_tnode *root = NULL;
        bool present[NKEYS] = {};
        for (int i = 0; i < NKEYS * 10; ++i) {
                int key = nrand48(random_state) % NKEYS;
_______________________________________________
svn-src-all@freebsd.org mailing list
https://lists.freebsd.org/mailman/listinfo/svn-src-all
To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"

Reply via email to