Re: compression of NSData... how to?
Re: compression of NSData... how to?
- Subject: Re: compression of NSData... how to?
- From: Benjámin Salánki <email@hidden>
- Date: Tue, 29 Aug 2006 15:55:16 +0200
Thank you, this looks promising. I'll take a look at it.
Ben
On Aug 29, 2006, at 12:01 PM, Fredrik Olsson wrote:
Benjámin Salánki skrev:
Hey there,
I'm looking for a way to compress my NSData before writing it to
file and then of course decompress it after reading it from file.
I looked at zlib, but to tell you the truth I couldn't get it to
work.
Is there a sample code snippet that I can take a look at? Can
anyone suggest a way to do this?
You can have mine, I have added compression and decompression as a
category to NSData, do not forget to link with zlib by adding -lz
to other linker flags. Change the AUTORELEASE and RELEASE macros to
normal release and autorelease messages if you need to, I jusy use
these macros not to forget to set pointers to nil for unused objects.
- (NSData *) compressedData
{
NSData *result = nil;
unsigned int srcLength = [self length];
if (srcLength > 0) {
uLong buffLength = srcLength * 1.001 + 12;
NSMutableData *compData = [[NSMutableData alloc]
initWithCapacity:buffLength];
[compData increaseLengthBy:buffLength];
int error = compress([compData mutableBytes], &buffLength,
[self bytes], srcLength);
switch( error ) {
case Z_OK:
[compData setLength: buffLength];
COPY(result, compData);
break;
default:
NSAssert(NO, @"Error compressing: Memory Error!");
break;
}
RELEASE(compData);
}
AUTORELEASE(result);
return result;
}
- (NSData *) decompressedData
{
if ([self length] == 0) return self;
unsigned full_length = [self length];
unsigned half_length = [self length] / 2;
NSMutableData *decompressed = [NSMutableData dataWithLength:
full_length + half_length];
BOOL done = NO;
int status;
z_stream strm;
strm.next_in = (Bytef *)[self bytes];
strm.avail_in = [self length];
strm.total_out = 0;
strm.zalloc = Z_NULL;
strm.zfree = Z_NULL;
strm.opaque = Z_NULL;
if (inflateInit(&strm) != Z_OK) {
return nil;
}
while (!done) {
// Make sure we have enough room and reset the lengths.
if (strm.total_out >= [decompressed length]) {
[decompressed increaseLengthBy: half_length];
}
strm.next_out = [decompressed mutableBytes] + strm.total_out;
strm.avail_out = [decompressed length] - strm.total_out;
// Inflate another chunk.
status = inflate (&strm, Z_SYNC_FLUSH);
if (status == Z_STREAM_END) {
done = YES;
} else if (status != Z_OK) {
break;
}
}
if (inflateEnd (&strm) != Z_OK) {
return nil;
}
// Set real length.
if (done) {
[decompressed setLength: strm.total_out];
return [NSData dataWithData: decompressed];
} else {
return nil;
}
}
// Fredrik Olsson
Thanks,
Ben
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