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/*
 * realloc.c
 * Fits System V requirements.
 * Knows format of malloc arena.
 */

#include <stdio.h>
#include <sys/malloc.h>

extern char *malloc();

char *
realloc(cp, size) register char *cp; unsigned size;
{
	register unsigned len, needed, nlen;
	register MBLOCK *mp, *nmp;

	if (cp == NULL)
		return malloc(size);
	else if (size == 0) {
		free(cp);
		return NULL;
	}

	/* Add space for blksize, round up to word boundary, fail if too big. */
	needed = roundup(size + sizeof(unsigned), BLOCKSIZE);
	if (needed < size)
		return NULL;

	/* Find mblock of the given cp and its length. */
	mp = mblockp(cp);
	len = realsize(mp->blksize);

	/* Request to shrink. */
	if (len >= needed) {
		if ((len -= needed) > LEASTFREE) {
			/* Split block into used and free parts. */
			mp->blksize = needed;
			mp = bumpp(mp, needed);
			mp->blksize = (len|FREE);
			__a_count++;
		}
		return cp;
	}

	/* Request to grow. */
	nmp = bumpp(mp, len);		/* next block */
	nlen = nmp->blksize;		/* length of next block (+1 if free) */
	if (isfree(nlen) && (nlen += len) > needed) {
		/* The next block is free and the two are big enough. */
		if ((nlen - needed) > LEASTFREE) {
			/* Combine blocks, split into used and free parts. */
			mp->blksize = needed;
			mp = bumpp(mp, needed);
			mp->blksize = nlen - needed;
		}
		else {	/* Combine blocks, using all of both. */
			mp->blksize = nlen = realsize(nlen);
			mp = bumpp(mp, nlen);
			__a_count--;
		}
		if (nmp == __a_scanp)
			__a_scanp = mp;
		return cp;
	}

	/* Otherwise, malloc new arena, copy current to it, free current. */
	if ((mp = (MBLOCK *)malloc(size)) == NULL)
		return NULL;
	memcpy(mp, cp, len - sizeof(unsigned));
	free(cp);
	return((char *)mp);
}

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