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Diffstat (limited to '3rd-party/xfpt/src/tree.c')
| -rw-r--r-- | 3rd-party/xfpt/src/tree.c | 216 |
1 files changed, 216 insertions, 0 deletions
diff --git a/3rd-party/xfpt/src/tree.c b/3rd-party/xfpt/src/tree.c new file mode 100644 index 000000000..e9825cbb3 --- /dev/null +++ b/3rd-party/xfpt/src/tree.c @@ -0,0 +1,216 @@ +/************************************************* +* xfpt - Simple ASCII->Docbook processor * +*************************************************/ + +/* Copyright (c) University of Cambridge, 2006 */ +/* Written by Philip Hazel. */ + +/* This module contains tree management routines. A tree is used for locally +defined entity values. */ + +#include "xfpt.h" + + +/*********************************************************** +* Binary Balanced Tree Management Routines * +***********************************************************/ + +/* This set of routines maintains a balanced binary tree using +the algorithm given in Knuth Vol 3 page 455. + +The routines make use of uschar * pointers as byte pointers, +so as to be able to do arithmetic on them, since ANSI Standard +C does not permit additions and subtractions on void pointers. */ + + +/************************************************* +* Flags and Parameters * +*************************************************/ + +#define tree_lbal 1 /* left subtree is longer */ +#define tree_rbal 2 /* right subtree is longer */ +#define tree_bmask 3 /* mask for flipping bits */ + + +/************************************************* +* Insert a new node into a tree * +*************************************************/ + +/* The node->name field must (obviously) be set, but the other +fields need not be initialized. + +Arguments: + treebase pointer to the root of the tree + node the note to insert, with name field set + +Returns: TRUE if node inserted; FALSE if not (duplicate) +*/ + +int +tree_insertnode(tree_node **treebase, tree_node *node) +{ +tree_node *p = *treebase; +tree_node **q, *r, *s, **t; +int a; + +node->left = node->right = NULL; +node->balance = 0; + +/* Deal with an empty tree */ + +if (p == NULL) + { + *treebase = node; + return TRUE; + } + +/* The tree is not empty. While finding the insertion point, +q points to the pointer to p, and t points to the pointer to +the potential re-balancing point. */ + +q = treebase; +t = q; + +/* Loop to search tree for place to insert new node */ + +for (;;) + { + int c = Ustrcmp(node->name, p->name); + if (c == 0) return FALSE; /* Duplicate node encountered */ + + /* Deal with climbing down the tree, exiting from the loop + when we reach a leaf. */ + + q = (c > 0)? &(p->right) : &(p->left); + p = *q; + if (p == NULL) break; + + /* Save the address of the pointer to the last node en route + which has a non-zero balance factor. */ + + if (p->balance != 0) t = q; + } + +/* When the above loop completes, q points to the pointer to NULL; +that is the place at which the new node must be inserted. */ + +*q = node; + +/* Set up s as the potential re-balancing point, and r as the +next node after it along the route. */ + +s = *t; +r = (Ustrcmp(node->name, s->name) > 0)? s->right : s->left; + +/* Adjust balance factors along the route from s to node. */ + +p = r; + +while (p != node) + { + if (Ustrcmp(node->name, p->name) < 0) + { + p->balance = tree_lbal; + p = p->left; + } + else + { + p->balance = tree_rbal; + p = p->right; + } + } + +/* Now the World-Famous Balancing Act */ + +a = (Ustrcmp(node->name, s->name) < 0)? tree_lbal : tree_rbal; + +if (s->balance == 0) s->balance = (uschar)a; /* The tree has grown higher */ + else if (s->balance != (uschar)a) s->balance = 0; /* It's become more balanced */ +else /* It's got out of balance */ + { + /* Perform a single rotation */ + + if (r->balance == (uschar)a) + { + p = r; + if (a == tree_rbal) + { + s->right = r->left; + r->left = s; + } + else + { + s->left = r->right; + r->right = s; + } + s->balance = 0; + r->balance = 0; + } + + /* Perform a double rotation There was an occasion when the balancing + factors were screwed up by a bug in the code that reads a tree from + the spool. In case this ever happens again, check for changing p to NULL + and don't do it. It is better to have an unbalanced tree than a crash. */ + + else + { + if (a == tree_rbal) + { + if (r->left == NULL) return TRUE; /* Bail out if tree corrupt */ + p = r->left; + r->left = p->right; + p->right = r; + s->right = p->left; + p->left = s; + } + else + { + if (r->right == NULL) return TRUE; /* Bail out if tree corrupt */ + p = r->right; + r->right = p->left; + p->left = r; + s->left = p->right; + p->right = s; + } + + s->balance = (p->balance == (uschar)a)? (uschar)(a^tree_bmask) : 0; + r->balance = (p->balance == (uschar)(a^tree_bmask))? (uschar)a : 0; + p->balance = 0; + } + + /* Finishing touch */ + + *t = p; + } + +return TRUE; /* Successful insertion */ +} + + + +/************************************************* +* Search tree for node by name * +*************************************************/ + +/* +Arguments: + p root of tree + name key to search for + +Returns: pointer to node, or NULL if not found +*/ + +tree_node * +tree_search(tree_node *p, uschar *name) +{ +while (p != NULL) + { + int c = Ustrcmp(name, p->name); + if (c == 0) return p; + p = (c < 0)? p->left : p->right; + } +return NULL; +} + + +/* End of tree.c */ |