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cordbscs.c

/*
 * 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;
      if (depth >= MAX_DEPTH) {
          return(CORD_balance((CORD)result));
      } else {
          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);
}

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