long mfseek(MEMFILE *mf,long offset,int whence)
{
long length;
assert(mf!=NULL);
if (mf->usedoffs == 0)
return 0L; /* early exit: not a single byte in the file */
/* find the size of the memory file */
length=mflength(mf);
/* convert the offset to an absolute position */
switch (whence) {
case SEEK_SET:
break;
case SEEK_CUR:
offset+=mf->offs;
break;
case SEEK_END:
assert(offset<=0);
offset+=length;
break;
} /* switch */
/* clamp to the file length limit */
if (offset<0)
offset=0;
else if (offset>length)
offset=length;
/* set new position and return it */
memfile_seek(mf, offset);
return offset;
}
unsigned int mfread(MEMFILE *mf,unsigned char *buffer,unsigned int size)
{
long length;
long numblocks;
int blockpos,blocksize;
unsigned int bytes;
MEMFILE *block;
assert(mf!=NULL);
/* adjust the size to read */
length=mflength(mf);
assert(mf->bufpos>=0 && mf->bufpos<=length);
if (mf->bufpos+size>(unsigned long)length)
size=(int)(length-mf->bufpos);
assert(mf->bufpos+size<=(unsigned long)length);
if (size==0)
return 0;
/* find the block to start reading from */
numblocks=mf->bufpos/BUFFERSIZE; /* # blocks to skip */
block=mf->next;
while (numblocks-->0) {
assert(block!=NULL);
block=block->next;
} /* while */
assert(block!=NULL);
/* copy out of memory */
bytes=0;
blockpos=(int)(mf->bufpos % BUFFERSIZE);
do {
blocksize=BUFFERSIZE-blockpos;
if ((unsigned int)blocksize>size)
blocksize=size;
assert(block!=NULL);
assert(block->bufpos>=0 && (unsigned long)block->bufpos<=BUFFERSIZE);
assert(blockpos+blocksize<=block->bufpos);
memcpy(buffer,block->buffer+blockpos,blocksize);
buffer+=blocksize;
size-=blocksize;
bytes+=blocksize;
block=block->next;
blockpos=0;
} while (size>0);
/* adjust file pointer */
mf->bufpos+=bytes;
return bytes;
}
unsigned int mfwrite(MEMFILE *mf,unsigned char *buffer,unsigned int size)
{
long length;
long numblocks;
int blockpos,blocksize;
unsigned int bytes;
MEMFILE *block;
assert(mf!=NULL);
/* see whether more memory must be allocated */
length=mflength(mf);
assert(mf->bufpos>=0 && mf->bufpos<=length);
numblocks=(length+BUFFERSIZE-1)/BUFFERSIZE; /* # allocated blocks */
while (mf->bufpos+size>numblocks*BUFFERSIZE) {
/* append a block */
MEMFILE *last;
block=(MEMFILE*)malloc(sizeof(MEMFILE));
if (block==NULL)
return 0;
memset(block,0,sizeof(MEMFILE));
block->buffer=(unsigned char*)malloc(BUFFERSIZE);
if (block->buffer==NULL) {
free(block);
return 0;
} /* if */
for (last=mf; last->next!=NULL; last=last->next)
/* nothing */;
assert(last!=NULL);
assert(last->next==NULL);
last->next=block;
numblocks++;
} /* while */
if (size==0)
return 0;
/* find the block to start writing to */
numblocks=mf->bufpos/BUFFERSIZE; /* # blocks to skip */
block=mf->next;
while (numblocks-->0) {
assert(block!=NULL);
block=block->next;
} /* while */
assert(block!=NULL);
/* copy into memory */
bytes=0;
blockpos=(int)(mf->bufpos % BUFFERSIZE);
do {
blocksize=BUFFERSIZE-blockpos;
assert(blocksize>=0);
if ((unsigned int)blocksize>size)
blocksize=size;
assert(block!=NULL);
memcpy(block->buffer+blockpos,buffer,blocksize);
buffer+=blocksize;
size-=blocksize;
bytes+=blocksize;
if (blockpos+blocksize>block->bufpos)
block->bufpos=blockpos+blocksize;
assert(block->bufpos>=0 && (unsigned long)block->bufpos<=BUFFERSIZE);
block=block->next;
blockpos=0;
} while (size>0);
/* adjust file pointer */
mf->bufpos+=bytes;
return bytes;
}
