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newstr.c

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/*
 * Copyright 1993, 1995 Christopher Seiwald.
 *
 * This file is part of Jam - see jam.c for Copyright information.
 */

# include "jam.h"
# include "newstr.h"
# include "hash.h"
# include <stddef.h>
# include <stdlib.h>

/*
 * newstr.c - string manipulation routines
 *
 * To minimize string copying, string creation, copying, and freeing
 * is done through newstr.
 *
 * External functions:
 *
 *    newstr() - return a dynamically allocated copy of a string
 *    copystr() - return a copy of a string previously returned by newstr()
 *    freestr() - free a string returned by newstr() or copystr()
 *    donestr() - free string tables
 *
 * Once a string is passed to newstr(), the returned string is readonly.
 *
 * This implementation builds a hash table of all strings, so that multiple 
 * calls of newstr() on the same string allocate memory for the string once.
 * Strings are never actually freed.
 */

typedef char *STRING;

static struct hash *strhash = 0;
static int strtotal = 0;

/*
 * Immortal string allocator implementation speeds string allocation
 * and cuts down on internal fragmentation
 */

# define STRING_BLOCK 4096
typedef struct strblock
{
    struct strblock* next;
    char data[STRING_BLOCK];
} strblock;

static strblock* strblock_chain = 0;

/* Storage remaining in the current strblock */
static char* storage_start = 0;
static char* storage_finish = 0;

/*
 * allocate() - Allocate n bytes of immortal string storage
 */
static char* allocate(size_t n)
{
    /* See if we can grab storage from an existing block */
    size_t remaining = storage_finish - storage_start;
    if ( remaining >= n )
    {
        char* result = storage_start;
        storage_start += n;
        return result;
    }
    else /* Must allocate a new block */
    {
        strblock* new_block;
        size_t nalloc = n;
        if ( nalloc < STRING_BLOCK )
            nalloc = STRING_BLOCK;

        /* allocate a new block and link into the chain */
        new_block = (strblock*)malloc( offsetof( strblock, data[0] ) + nalloc * sizeof(new_block->data[0]) );
        if ( new_block == 0 )
            return 0;
        new_block->next = strblock_chain;
        strblock_chain = new_block;

        /* Take future allocations out of the larger remaining space */
        if ( remaining < nalloc - n )
        {
            storage_start = new_block->data + n;
            storage_finish = new_block->data + nalloc;
        }
        return new_block->data;
    }
}

/*
 * newstr() - return a dynamically allocated copy of a string
 */

char *
newstr( char *string )
{
        STRING str, *s = &str;

        if( !strhash )
            strhash = hashinit( sizeof( STRING ), "strings" );

        *s = string;

        if( hashenter( strhash, (HASHDATA **)&s ) )
        {
            int l = strlen( string );
            char *m = (char *)allocate( l + 1 );

            strtotal += l + 1;
            memcpy( m, string, l + 1 );
            *s = m;
        }

        return *s;
}

/*
 * copystr() - return a copy of a string previously returned by newstr()
 */

char *
copystr( char *s )
{
        return s;
}

/*
 * freestr() - free a string returned by newstr() or copystr()
 */

void
freestr( char *s )
{
}

/*
 * donestr() - free string tables
 */

void
donestr()
{
    /* Reclaim string blocks */
    while ( strblock_chain != 0 )
    {
        strblock* n = strblock_chain->next;
        free(strblock_chain);
        strblock_chain = n;
    }
    
    hashdone( strhash );
    
    if( DEBUG_MEM )
        printf( "%dK in strings\n", strtotal / 1024 );
}

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