cordbscs.c

A garbage collector for C and 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 ([e-mail])
 */
/* 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));
}