Initial revision

1 files changed, 915 insertions, 0 deletions

diff --git a/gc/cord/cordbscs.c b/gc/cord/cordbscs.c
new file mode 100644
index 0000000..9fc894d
--- /dev/null
+++ b/gc/cord/cordbscs.c
@@ -0,0 +1,915 @@
+/*
+ * Copyright (c) 1993-1994 by Xerox Corporation.  All rights reserved.
+ *
+ * THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
+ * OR IMPLIED.  ANY USE IS AT YOUR OWN RISK.
+ *
+ * Permission is hereby granted to use or copy this program
+ * for any purpose,  provided the above notices are retained on all copies.
+ * Permission to modify the code and to distribute modified code is granted,
+ * provided the above notices are retained, and a notice that the code was
+ * modified is included with the above copyright notice.
+ *
+ * Author: Hans-J. Boehm (boehm@parc.xerox.com)
+ */
+/* Boehm, October 3, 1994 5:19 pm PDT */
+# include "gc.h"
+# include "cord.h"
+# include <stdlib.h>
+# include <stdio.h>
+# include <string.h>
+
+/* An implementation of the cord primitives.  These are the only 	*/
+/* Functions that understand the representation.  We perform only	*/
+/* minimal checks on arguments to these functions.  Out of bounds	*/
+/* arguments to the iteration functions may result in client functions	*/
+/* invoked on garbage data.  In most cases, client functions should be	*/
+/* programmed defensively enough that this does not result in memory	*/
+/* smashes.								*/ 
+
+typedef void (* oom_fn)(void);
+
+oom_fn CORD_oom_fn = (oom_fn) 0;
+
+# define OUT_OF_MEMORY {  if (CORD_oom_fn != (oom_fn) 0) (*CORD_oom_fn)(); \
+			  ABORT("Out of memory\n"); }
+# define ABORT(msg) { fprintf(stderr, "%s\n", msg); abort(); }
+
+typedef unsigned long word;
+
+typedef union {
+    struct Concatenation {
+    	char null;
+	char header;
+	char depth;	/* concatenation nesting depth. */
+	unsigned char left_len;
+			/* Length of left child if it is sufficiently	*/
+			/* short; 0 otherwise.				*/
+#	    define MAX_LEFT_LEN 255
+	word len;
+	CORD left;	/* length(left) > 0	*/
+	CORD right;	/* length(right) > 0	*/
+    } concatenation;
+    struct Function {
+	char null;
+	char header;
+	char depth;	/* always 0	*/
+	char left_len;	/* always 0	*/
+	word len;
+	CORD_fn fn;
+	void * client_data;
+    } function;
+    struct Generic {
+    	char null;
+	char header;
+	char depth;
+	char left_len;
+	word len;
+    } generic;
+    char string[1];
+} CordRep;
+
+# define CONCAT_HDR 1
+	
+# define FN_HDR 4
+# define SUBSTR_HDR 6
+	/* Substring nodes are a special case of function nodes.  	*/
+	/* The client_data field is known to point to a substr_args	*/
+	/* structure, and the function is either CORD_apply_access_fn 	*/
+	/* or CORD_index_access_fn.					*/
+
+/* The following may be applied only to function and concatenation nodes: */
+#define IS_CONCATENATION(s)  (((CordRep *)s)->generic.header == CONCAT_HDR)
+
+#define IS_FUNCTION(s)  ((((CordRep *)s)->generic.header & FN_HDR) != 0)
+
+#define IS_SUBSTR(s) (((CordRep *)s)->generic.header == SUBSTR_HDR)
+
+#define LEN(s) (((CordRep *)s) -> generic.len)
+#define DEPTH(s) (((CordRep *)s) -> generic.depth)
+#define GEN_LEN(s) (CORD_IS_STRING(s) ? strlen(s) : LEN(s))
+
+#define LEFT_LEN(c) ((c) -> left_len != 0? \
+				(c) -> left_len \
+				: (CORD_IS_STRING((c) -> left) ? \
+					(c) -> len - GEN_LEN((c) -> right) \
+					: LEN((c) -> left)))
+
+#define SHORT_LIMIT (sizeof(CordRep) - 1)
+	/* Cords shorter than this are C strings */
+
+
+/* Dump the internal representation of x to stdout, with initial 	*/
+/* indentation level n.							*/
+void CORD_dump_inner(CORD x, unsigned n)
+{
+    register size_t i;
+    
+    for (i = 0; i < (size_t)n; i++) {
+        fputs("  ", stdout);
+    }
+    if (x == 0) {
+      	fputs("NIL\n", stdout);
+    } else if (CORD_IS_STRING(x)) {
+        for (i = 0; i <= SHORT_LIMIT; i++) {
+            if (x[i] == '\0') break;
+            putchar(x[i]);
+        }
+        if (x[i] != '\0') fputs("...", stdout);
+        putchar('\n');
+    } else if (IS_CONCATENATION(x)) {
+        register struct Concatenation * conc =
+        			&(((CordRep *)x) -> concatenation);
+        printf("Concatenation: %p (len: %d, depth: %d)\n",
+               x, (int)(conc -> len), (int)(conc -> depth));
+        CORD_dump_inner(conc -> left, n+1);
+        CORD_dump_inner(conc -> right, n+1);
+    } else /* function */{
+        register struct Function * func =
+        			&(((CordRep *)x) -> function);
+        if (IS_SUBSTR(x)) printf("(Substring) ");
+        printf("Function: %p (len: %d): ", x, (int)(func -> len));
+        for (i = 0; i < 20 && i < func -> len; i++) {
+            putchar((*(func -> fn))(i, func -> client_data));
+        }
+        if (i < func -> len) fputs("...", stdout);
+        putchar('\n');
+    }
+}
+
+/* Dump the internal representation of x to stdout	*/
+void CORD_dump(CORD x)
+{
+    CORD_dump_inner(x, 0);
+    fflush(stdout);
+}
+
+CORD CORD_cat_char_star(CORD x, const char * y, size_t leny)
+{
+    register size_t result_len;
+    register size_t lenx;
+    register int depth;
+    
+    if (x == CORD_EMPTY) return(y);
+    if (leny == 0) return(x);
+    if (CORD_IS_STRING(x)) {
+        lenx = strlen(x);
+        result_len = lenx + leny;
+        if (result_len <= SHORT_LIMIT) {
+            register char * result = GC_MALLOC_ATOMIC(result_len+1);
+        
+            if (result == 0) OUT_OF_MEMORY;
+            memcpy(result, x, lenx);
+            memcpy(result + lenx, y, leny);
+            result[result_len] = '\0';
+            return((CORD) result);
+        } else {
+            depth = 1;
+        }
+    } else {
+    	register CORD right;
+    	register CORD left;
+    	register char * new_right;
+    	register size_t right_len;
+    	
+    	lenx = LEN(x);
+    	
+        if (leny <= SHORT_LIMIT/2
+    	    && IS_CONCATENATION(x)
+            && CORD_IS_STRING(right = ((CordRep *)x) -> concatenation.right)) {
+            /* Merge y into right part of x. */
+            if (!CORD_IS_STRING(left = ((CordRep *)x) -> concatenation.left)) {
+            	right_len = lenx - LEN(left);
+            } else if (((CordRep *)x) -> concatenation.left_len != 0) {
+                right_len = lenx - ((CordRep *)x) -> concatenation.left_len;
+            } else {
+            	right_len = strlen(right);
+            }
+            result_len = right_len + leny;  /* length of new_right */
+            if (result_len <= SHORT_LIMIT) {
+            	new_right = GC_MALLOC_ATOMIC(result_len + 1);
+            	memcpy(new_right, right, right_len);
+            	memcpy(new_right + right_len, y, leny);
+            	new_right[result_len] = '\0';
+            	y = new_right;
+            	leny = result_len;
+            	x = left;
+            	lenx -= right_len;
+            	/* Now fall through to concatenate the two pieces: */
+            }
+            if (CORD_IS_STRING(x)) {
+                depth = 1;
+            } else {
+                depth = DEPTH(x) + 1;
+            }
+        } else {
+            depth = DEPTH(x) + 1;
+        }
+        result_len = lenx + leny;
+    }
+    {
+      /* The general case; lenx, result_len is known: */
+    	register struct Concatenation * result;
+    	
+    	result = GC_NEW(struct Concatenation);
+    	if (result == 0) OUT_OF_MEMORY;
+    	result->header = CONCAT_HDR;
+    	result->depth = depth;
+    	if (lenx <= MAX_LEFT_LEN) result->left_len = lenx;
+    	result->len = result_len;
+    	result->left = x;
+    	result->right = y;
+    	if (depth > MAX_DEPTH) {
+    	    return(CORD_balance((CORD)result));
+    	} else {
+    	    return((CORD) result);
+    	}
+    }
+}
+
+
+CORD CORD_cat(CORD x, CORD y)
+{
+    register size_t result_len;
+    register int depth;
+    register size_t lenx;
+    
+    if (x == CORD_EMPTY) return(y);
+    if (y == CORD_EMPTY) return(x);
+    if (CORD_IS_STRING(y)) {
+        return(CORD_cat_char_star(x, y, strlen(y)));
+    } else if (CORD_IS_STRING(x)) {
+        lenx = strlen(x);
+        depth = DEPTH(y) + 1;
+    } else {
+        register int depthy = DEPTH(y);
+        
+        lenx = LEN(x);
+        depth = DEPTH(x) + 1;
+        if (depthy >= depth) depth = depthy + 1;
+    }
+    result_len = lenx + LEN(y);
+    {
+    	register struct Concatenation * result;
+    	
+    	result = GC_NEW(struct Concatenation);
+    	if (result == 0) OUT_OF_MEMORY;
+    	result->header = CONCAT_HDR;
+    	result->depth = depth;
+    	if (lenx <= MAX_LEFT_LEN) result->left_len = lenx;
+    	result->len = result_len;
+    	result->left = x;
+    	result->right = y;
+    	return((CORD) result);
+    }
+}
+
+
+
+CORD CORD_from_fn(CORD_fn fn, void * client_data, size_t len)
+{
+    if (len <= 0) return(0);
+    if (len <= SHORT_LIMIT) {
+        register char * result;
+        register size_t i;
+        char buf[SHORT_LIMIT+1];
+        register char c;
+        
+        for (i = 0; i < len; i++) {
+            c = (*fn)(i, client_data);
+            if (c == '\0') goto gen_case;
+            buf[i] = c;
+        }
+        buf[i] = '\0';
+        result = GC_MALLOC_ATOMIC(len+1);
+        if (result == 0) OUT_OF_MEMORY;
+        strcpy(result, buf);
+        result[len] = '\0';
+        return((CORD) result);
+    }
+  gen_case:
+    {
+    	register struct Function * result;
+    	
+    	result = GC_NEW(struct Function);
+    	if (result == 0) OUT_OF_MEMORY;
+    	result->header = FN_HDR;
+    	/* depth is already 0 */
+    	result->len = len;
+    	result->fn = fn;
+    	result->client_data = client_data;
+    	return((CORD) result);
+    }
+}
+
+size_t CORD_len(CORD x)
+{
+    if (x == 0) {
+     	return(0);
+    } else {
+	return(GEN_LEN(x));
+    }
+}
+
+struct substr_args {
+    CordRep * sa_cord;
+    size_t sa_index;
+};
+
+char CORD_index_access_fn(size_t i, void * client_data)
+{
+    register struct substr_args *descr = (struct substr_args *)client_data;
+    
+    return(((char *)(descr->sa_cord))[i + descr->sa_index]);
+}
+
+char CORD_apply_access_fn(size_t i, void * client_data)
+{
+    register struct substr_args *descr = (struct substr_args *)client_data;
+    register struct Function * fn_cord = &(descr->sa_cord->function);
+    
+    return((*(fn_cord->fn))(i + descr->sa_index, fn_cord->client_data));
+}
+
+/* A version of CORD_substr that simply returns a function node, thus	*/
+/* postponing its work.	The fourth argument is a function that may	*/
+/* be used for efficient access to the ith character.			*/
+/* Assumes i >= 0 and i + n < length(x).				*/
+CORD CORD_substr_closure(CORD x, size_t i, size_t n, CORD_fn f)
+{
+    register struct substr_args * sa = GC_NEW(struct substr_args);
+    CORD result;
+    
+    if (sa == 0) OUT_OF_MEMORY;
+    sa->sa_cord = (CordRep *)x;
+    sa->sa_index = i;
+    result = CORD_from_fn(f, (void *)sa, n);
+    ((CordRep *)result) -> function.header = SUBSTR_HDR;
+    return (result);
+}
+
+# define SUBSTR_LIMIT (10 * SHORT_LIMIT)
+	/* Substrings of function nodes and flat strings shorter than 	*/
+	/* this are flat strings.  Othewise we use a functional 	*/
+	/* representation, which is significantly slower to access.	*/
+
+/* A version of CORD_substr that assumes i >= 0, n > 0, and i + n < length(x).*/
+CORD CORD_substr_checked(CORD x, size_t i, size_t n)
+{
+    if (CORD_IS_STRING(x)) {
+        if (n > SUBSTR_LIMIT) {
+            return(CORD_substr_closure(x, i, n, CORD_index_access_fn));
+        } else {
+            register char * result = GC_MALLOC_ATOMIC(n+1);
+            
+            if (result == 0) OUT_OF_MEMORY;
+            strncpy(result, x+i, n);
+            result[n] = '\0';
+            return(result);
+        }
+    } else if (IS_CONCATENATION(x)) {
+    	register struct Concatenation * conc
+    			= &(((CordRep *)x) -> concatenation);
+    	register size_t left_len;
+    	register size_t right_len;
+    	
+    	left_len = LEFT_LEN(conc);
+    	right_len = conc -> len - left_len;
+    	if (i >= left_len) {
+    	    if (n == right_len) return(conc -> right);
+    	    return(CORD_substr_checked(conc -> right, i - left_len, n));
+    	} else if (i+n <= left_len) {
+    	    if (n == left_len) return(conc -> left);
+    	    return(CORD_substr_checked(conc -> left, i, n));
+    	} else {
+    	    /* Need at least one character from each side. */
+    	    register CORD left_part;
+    	    register CORD right_part;
+    	    register size_t left_part_len = left_len - i;
+     	
+    	    if (i == 0) {
+    	        left_part = conc -> left;
+    	    } else {
+    	        left_part = CORD_substr_checked(conc -> left, i, left_part_len);
+    	    }
+    	    if (i + n == right_len + left_len) {
+    	         right_part = conc -> right;
+    	    } else {
+    	         right_part = CORD_substr_checked(conc -> right, 0,
+    	    				          n - left_part_len);
+    	    }
+    	    return(CORD_cat(left_part, right_part));
+    	}
+    } else /* function */ {
+        if (n > SUBSTR_LIMIT) {
+            if (IS_SUBSTR(x)) {
+            	/* Avoid nesting substring nodes.	*/
+            	register struct Function * f = &(((CordRep *)x) -> function);
+            	register struct substr_args *descr =
+            			(struct substr_args *)(f -> client_data);
+            	
+            	return(CORD_substr_closure((CORD)descr->sa_cord,
+            				   i + descr->sa_index,
+            				   n, f -> fn));
+            } else {
+                return(CORD_substr_closure(x, i, n, CORD_apply_access_fn));
+            }
+        } else {
+            char * result;
+            register struct Function * f = &(((CordRep *)x) -> function);
+            char buf[SUBSTR_LIMIT+1];
+            register char * p = buf;
+            register char c;
+            register int j;
+            register int lim = i + n;
+            
+            for (j = i; j < lim; j++) {
+            	c = (*(f -> fn))(j, f -> client_data);
+            	if (c == '\0') {
+            	    return(CORD_substr_closure(x, i, n, CORD_apply_access_fn));
+            	}
+            	*p++ = c;
+            }
+            *p = '\0';
+            result = GC_MALLOC_ATOMIC(n+1);
+            if (result == 0) OUT_OF_MEMORY;
+            strcpy(result, buf);
+            return(result);
+        }
+    }
+}
+
+CORD CORD_substr(CORD x, size_t i, size_t n)
+{
+    register size_t len = CORD_len(x);
+    
+    if (i >= len || n <= 0) return(0);
+    	/* n < 0 is impossible in a correct C implementation, but	*/
+    	/* quite possible  under SunOS 4.X.				*/
+    if (i + n > len) n = len - i;
+#   ifndef __STDC__
+      if (i < 0) ABORT("CORD_substr: second arg. negative");
+    	/* Possible only if both client and C implementation are buggy.	*/
+    	/* But empirically this happens frequently.			*/
+#   endif
+    return(CORD_substr_checked(x, i, n));
+}
+
+/* See cord.h for definition.  We assume i is in range.	*/
+int CORD_iter5(CORD x, size_t i, CORD_iter_fn f1,
+			 CORD_batched_iter_fn f2, void * client_data)
+{
+    if (x == 0) return(0);
+    if (CORD_IS_STRING(x)) {
+    	register const char *p = x+i;
+    	
+    	if (*p == '\0') ABORT("2nd arg to CORD_iter5 too big");
+        if (f2 != CORD_NO_FN) {
+            return((*f2)(p, client_data));
+        } else {
+	    while (*p) {
+                if ((*f1)(*p, client_data)) return(1);
+                p++;
+	    }
+	    return(0);
+        }
+    } else if (IS_CONCATENATION(x)) {
+    	register struct Concatenation * conc
+    			= &(((CordRep *)x) -> concatenation);
+    	
+    	
+    	if (i > 0) {
+    	    register size_t left_len = LEFT_LEN(conc);
+    	    
+    	    if (i >= left_len) {
+    	        return(CORD_iter5(conc -> right, i - left_len, f1, f2,
+    	        		  client_data));
+    	    }
+    	}
+    	if (CORD_iter5(conc -> left, i, f1, f2, client_data)) {
+    	    return(1);
+    	}
+    	return(CORD_iter5(conc -> right, 0, f1, f2, client_data));
+    } else /* function */ {
+        register struct Function * f = &(((CordRep *)x) -> function);
+        register size_t j;
+        register size_t lim = f -> len;
+        
+        for (j = i; j < lim; j++) {
+            if ((*f1)((*(f -> fn))(j, f -> client_data), client_data)) {
+                return(1);
+            }
+        }
+        return(0);
+    }
+}
+			
+#undef CORD_iter
+int CORD_iter(CORD x, CORD_iter_fn f1, void * client_data)
+{
+    return(CORD_iter5(x, 0, f1, CORD_NO_FN, client_data));
+}
+
+int CORD_riter4(CORD x, size_t i, CORD_iter_fn f1, void * client_data)
+{
+    if (x == 0) return(0);
+    if (CORD_IS_STRING(x)) {
+	register const char *p = x + i;
+	register char c;
+               
+	for(;;) {
+	    c = *p;
+	    if (c == '\0') ABORT("2nd arg to CORD_riter4 too big");
+            if ((*f1)(c, client_data)) return(1);
+	    if (p == x) break;
+            p--;
+	}
+	return(0);
+    } else if (IS_CONCATENATION(x)) {
+    	register struct Concatenation * conc
+    			= &(((CordRep *)x) -> concatenation);
+    	register CORD left_part = conc -> left;
+    	register size_t left_len;
+    	
+    	left_len = LEFT_LEN(conc);
+    	if (i >= left_len) {
+    	    if (CORD_riter4(conc -> right, i - left_len, f1, client_data)) {
+    	    	return(1);
+    	    }
+    	    return(CORD_riter4(left_part, left_len - 1, f1, client_data));
+    	} else {
+    	    return(CORD_riter4(left_part, i, f1, client_data));
+    	}
+    } else /* function */ {
+        register struct Function * f = &(((CordRep *)x) -> function);
+        register size_t j;
+        
+        for (j = i; ; j--) {
+            if ((*f1)((*(f -> fn))(j, f -> client_data), client_data)) {
+                return(1);
+            }
+            if (j == 0) return(0);
+        }
+    }
+}
+
+int CORD_riter(CORD x, CORD_iter_fn f1, void * client_data)
+{
+    return(CORD_riter4(x, CORD_len(x) - 1, f1, client_data));
+}
+
+/*
+ * The following functions are concerned with balancing cords.
+ * Strategy:
+ * Scan the cord from left to right, keeping the cord scanned so far
+ * as a forest of balanced trees of exponentialy decreasing length.
+ * When a new subtree needs to be added to the forest, we concatenate all
+ * shorter ones to the new tree in the appropriate order, and then insert
+ * the result into the forest.
+ * Crucial invariants:
+ * 1. The concatenation of the forest (in decreasing order) with the
+ *     unscanned part of the rope is equal to the rope being balanced.
+ * 2. All trees in the forest are balanced.
+ * 3. forest[i] has depth at most i.
+ */
+
+typedef struct {
+    CORD c;
+    size_t len;		/* Actual length of c 	*/
+} ForestElement;
+
+static size_t min_len [ MAX_DEPTH ];
+
+static int min_len_init = 0;
+
+int CORD_max_len;
+
+typedef ForestElement Forest [ MAX_DEPTH ];
+			/* forest[i].len >= fib(i+1)	        */
+			/* The string is the concatenation	*/
+			/* of the forest in order of DECREASING */
+			/* indices.				*/
+
+void CORD_init_min_len()
+{
+    register int i;
+    register size_t last, previous, current;
+        
+    min_len[0] = previous = 1;
+    min_len[1] = last = 2;
+    for (i = 2; i < MAX_DEPTH; i++) {
+    	current = last + previous;
+    	if (current < last) /* overflow */ current = last;
+    	min_len[i] = current;
+    	previous = last;
+    	last = current;
+    }
+    CORD_max_len = last - 1;
+    min_len_init = 1;
+}
+
+
+void CORD_init_forest(ForestElement * forest, size_t max_len)
+{
+    register int i;
+    
+    for (i = 0; i < MAX_DEPTH; i++) {
+    	forest[i].c = 0;
+    	if (min_len[i] > max_len) return;
+    }
+    ABORT("Cord too long");
+}
+
+/* Add a leaf to the appropriate level in the forest, cleaning		*/
+/* out lower levels as necessary.					*/
+/* Also works if x is a balanced tree of concatenations; however	*/
+/* in this case an extra concatenation node may be inserted above x;	*/
+/* This node should not be counted in the statement of the invariants.	*/
+void CORD_add_forest(ForestElement * forest, CORD x, size_t len)
+{
+    register int i = 0;
+    register CORD sum = CORD_EMPTY;
+    register size_t sum_len = 0;
+    
+    while (len > min_len[i + 1]) {
+    	if (forest[i].c != 0) {
+    	    sum = CORD_cat(forest[i].c, sum);
+    	    sum_len += forest[i].len;
+    	    forest[i].c = 0;
+    	}
+        i++;
+    }
+    /* Sum has depth at most 1 greter than what would be required 	*/
+    /* for balance.							*/
+    sum = CORD_cat(sum, x);
+    sum_len += len;
+    /* If x was a leaf, then sum is now balanced.  To see this		*/
+    /* consider the two cases in which forest[i-1] either is or is 	*/
+    /* not empty.							*/
+    while (sum_len >= min_len[i]) {
+    	if (forest[i].c != 0) {
+    	    sum = CORD_cat(forest[i].c, sum);
+    	    sum_len += forest[i].len;
+    	    /* This is again balanced, since sum was balanced, and has	*/
+    	    /* allowable depth that differs from i by at most 1.	*/
+    	    forest[i].c = 0;
+    	}
+        i++;
+    }
+    i--;
+    forest[i].c = sum;
+    forest[i].len = sum_len;
+}
+
+CORD CORD_concat_forest(ForestElement * forest, size_t expected_len)
+{
+    register int i = 0;
+    CORD sum = 0;
+    size_t sum_len = 0;
+    
+    while (sum_len != expected_len) {
+    	if (forest[i].c != 0) {
+    	    sum = CORD_cat(forest[i].c, sum);
+    	    sum_len += forest[i].len;
+    	}
+        i++;
+    }
+    return(sum);
+}
+
+/* Insert the frontier of x into forest.  Balanced subtrees are	*/
+/* treated as leaves.  This potentially adds one to the depth	*/
+/* of the final tree.						*/
+void CORD_balance_insert(CORD x, size_t len, ForestElement * forest)
+{
+    register int depth;
+    
+    if (CORD_IS_STRING(x)) {
+        CORD_add_forest(forest, x, len);
+    } else if (IS_CONCATENATION(x)
+               && ((depth = DEPTH(x)) >= MAX_DEPTH
+                   || len < min_len[depth])) {
+    	register struct Concatenation * conc
+    			= &(((CordRep *)x) -> concatenation);
+    	size_t left_len = LEFT_LEN(conc);
+    	
+    	CORD_balance_insert(conc -> left, left_len, forest);
+    	CORD_balance_insert(conc -> right, len - left_len, forest);
+    } else /* function or balanced */ {
+    	CORD_add_forest(forest, x, len);
+    }
+}
+
+
+CORD CORD_balance(CORD x)
+{
+    Forest forest;
+    register size_t len;
+    
+    if (x == 0) return(0);
+    if (CORD_IS_STRING(x)) return(x);
+    if (!min_len_init) CORD_init_min_len();
+    len = LEN(x);
+    CORD_init_forest(forest, len);
+    CORD_balance_insert(x, len, forest);
+    return(CORD_concat_forest(forest, len));
+}
+
+
+/* Position primitives	*/
+
+/* Private routines to deal with the hard cases only: */
+
+/* P contains a prefix of the  path to cur_pos.	Extend it to a full	*/
+/* path and set up leaf info.						*/
+/* Return 0 if past the end of cord, 1 o.w.				*/
+void CORD__extend_path(register CORD_pos p)
+{
+     register struct CORD_pe * current_pe = &(p[0].path[p[0].path_len]);
+     register CORD top = current_pe -> pe_cord;
+     register size_t pos = p[0].cur_pos;
+     register size_t top_pos = current_pe -> pe_start_pos;
+     register size_t top_len = GEN_LEN(top);
+     
+     /* Fill in the rest of the path. */
+       while(!CORD_IS_STRING(top) && IS_CONCATENATION(top)) {
+     	 register struct Concatenation * conc =
+     	 		&(((CordRep *)top) -> concatenation);
+     	 register size_t left_len;
+     	 
+     	 left_len = LEFT_LEN(conc);
+     	 current_pe++;
+     	 if (pos >= top_pos + left_len) {
+     	     current_pe -> pe_cord = top = conc -> right;
+     	     current_pe -> pe_start_pos = top_pos = top_pos + left_len;
+     	     top_len -= left_len;
+     	 } else {
+     	     current_pe -> pe_cord = top = conc -> left;
+     	     current_pe -> pe_start_pos = top_pos;
+     	     top_len = left_len;
+     	 }
+     	 p[0].path_len++;
+       }
+     /* Fill in leaf description for fast access. */
+       if (CORD_IS_STRING(top)) {
+         p[0].cur_leaf = top;
+         p[0].cur_start = top_pos;
+         p[0].cur_end = top_pos + top_len;
+       } else {
+         p[0].cur_end = 0;
+       }
+       if (pos >= top_pos + top_len) p[0].path_len = CORD_POS_INVALID;
+}
+
+char CORD__pos_fetch(register CORD_pos p)
+{
+    /* Leaf is a function node */
+    struct CORD_pe * pe = &((p)[0].path[(p)[0].path_len]);
+    CORD leaf = pe -> pe_cord;
+    register struct Function * f = &(((CordRep *)leaf) -> function);
+    
+    if (!IS_FUNCTION(leaf)) ABORT("CORD_pos_fetch: bad leaf");
+    return ((*(f -> fn))(p[0].cur_pos - pe -> pe_start_pos, f -> client_data));
+}
+
+void CORD__next(register CORD_pos p)
+{
+    register size_t cur_pos = p[0].cur_pos + 1;
+    register struct CORD_pe * current_pe = &((p)[0].path[(p)[0].path_len]);
+    register CORD leaf = current_pe -> pe_cord;
+    
+    /* Leaf is not a string or we're at end of leaf */
+    p[0].cur_pos = cur_pos;
+    if (!CORD_IS_STRING(leaf)) {
+    	/* Function leaf	*/
+    	register struct Function * f = &(((CordRep *)leaf) -> function);
+    	register size_t start_pos = current_pe -> pe_start_pos;
+    	register size_t end_pos = start_pos + f -> len;
+    	
+    	if (cur_pos < end_pos) {
+    	  /* Fill cache and return. */
+    	    register size_t i;
+    	    register size_t limit = cur_pos + FUNCTION_BUF_SZ;
+    	    register CORD_fn fn = f -> fn;
+    	    register void * client_data = f -> client_data;
+    	    
+    	    if (limit > end_pos) {
+    	        limit = end_pos;
+    	    }
+    	    for (i = cur_pos; i < limit; i++) {
+    	        p[0].function_buf[i - cur_pos] =
+    	        	(*fn)(i - start_pos, client_data);
+    	    }
+    	    p[0].cur_start = cur_pos;
+    	    p[0].cur_leaf = p[0].function_buf;
+    	    p[0].cur_end = limit;
+    	    return;
+    	}
+    }
+    /* End of leaf	*/
+    /* Pop the stack until we find two concatenation nodes with the 	*/
+    /* same start position: this implies we were in left part.		*/
+    {
+    	while (p[0].path_len > 0
+    	       && current_pe[0].pe_start_pos != current_pe[-1].pe_start_pos) {
+    	    p[0].path_len--;
+    	    current_pe--;
+    	}
+    	if (p[0].path_len == 0) {
+	    p[0].path_len = CORD_POS_INVALID;
+            return;
+	}
+    }
+    p[0].path_len--;
+    CORD__extend_path(p);
+}
+
+void CORD__prev(register CORD_pos p)
+{
+    register struct CORD_pe * pe = &(p[0].path[p[0].path_len]);
+    
+    if (p[0].cur_pos == 0) {
+        p[0].path_len = CORD_POS_INVALID;
+        return;
+    }
+    p[0].cur_pos--;
+    if (p[0].cur_pos >= pe -> pe_start_pos) return;
+    
+    /* Beginning of leaf	*/
+    
+    /* Pop the stack until we find two concatenation nodes with the 	*/
+    /* different start position: this implies we were in right part.	*/
+    {
+    	register struct CORD_pe * current_pe = &((p)[0].path[(p)[0].path_len]);
+    	
+    	while (p[0].path_len > 0
+    	       && current_pe[0].pe_start_pos == current_pe[-1].pe_start_pos) {
+    	    p[0].path_len--;
+    	    current_pe--;
+    	}
+    }
+    p[0].path_len--;
+    CORD__extend_path(p);
+}
+
+#undef CORD_pos_fetch
+#undef CORD_next
+#undef CORD_prev
+#undef CORD_pos_to_index
+#undef CORD_pos_to_cord
+#undef CORD_pos_valid
+
+char CORD_pos_fetch(register CORD_pos p)
+{
+    if (p[0].cur_start <= p[0].cur_pos && p[0].cur_pos < p[0].cur_end) {
+    	return(p[0].cur_leaf[p[0].cur_pos - p[0].cur_start]);
+    } else {
+        return(CORD__pos_fetch(p));
+    }
+}
+
+void CORD_next(CORD_pos p)
+{
+    if (p[0].cur_pos < p[0].cur_end - 1) {
+    	p[0].cur_pos++;
+    } else {
+    	CORD__next(p);
+    }
+}
+
+void CORD_prev(CORD_pos p)
+{
+    if (p[0].cur_end != 0 && p[0].cur_pos > p[0].cur_start) {
+    	p[0].cur_pos--;
+    } else {
+    	CORD__prev(p);
+    }
+}
+
+size_t CORD_pos_to_index(CORD_pos p)
+{
+    return(p[0].cur_pos);
+}
+
+CORD CORD_pos_to_cord(CORD_pos p)
+{
+    return(p[0].path[0].pe_cord);
+}
+
+int CORD_pos_valid(CORD_pos p)
+{
+    return(p[0].path_len != CORD_POS_INVALID);
+}
+
+void CORD_set_pos(CORD_pos p, CORD x, size_t i)
+{
+    if (x == CORD_EMPTY) {
+    	p[0].path_len = CORD_POS_INVALID;
+    	return;
+    }
+    p[0].path[0].pe_cord = x;
+    p[0].path[0].pe_start_pos = 0;
+    p[0].path_len = 0;
+    p[0].cur_pos = i;
+    CORD__extend_path(p);
+}