Pack.writeInt()

[Phil Rhodes]

Hi,

 

I'm having trouble writing 8-byte ints (QWORDs) to Pack instances:

 

var foo = new Buffer();

var bar = new Pack(Buffer);

var largeNumber = Math.pow(2^63);

bar.writeInt(largeNumber,8);

 

> struct3.js:123: Error: Unable to manage this size.

 

This does not occur with four-byte ints.

 

I'm writing a custom chunk into a RIFF WAVE file which includes a time reference value as a number of audio samples in <24 hours. Since the number of 48KHz PCM audio samples in up-to-24 hours may be very large, the format uses a QWORD.

 

P

[soubok]

Hi,
Tracemonkey is not able to manage 64bit integers natively. However, a
big integer can be stored in a double data type without loosing
precision using the mantissa bits only.
This mean that 2^53 will be the higher integer value you will be able
to manage in pure JavaScript.
If it is not suitable, the only alternative will be to split your
64bit integer in two 32bit integers.

Franck.

[Phil Rhodes]

The maximum (sane) value for this field is 16588800000.

I don't know if I can get away with that :)

P

[Phil Rhodes]

Here's what I came up with, anyway:


if (this.byteLen === 8) {
packer.writeInt(this.value >> 32, 4); // big
packer.writeInt(this.value & 0xFFFFFFFF, 4); // little
} else {
packer.writeInt(this.value, this.byteLen);
}

[soubok]

On Tue, Dec 15, 2009 at 00:14, Phil Rhodes <phil_...@rocketmail.com> wrote:
> The maximum (sane) value for this field is 16588800000.

I can support integers from -9007199254740991 to +9007199254740991

>
> I don't know if I can get away with that :)
>
> P
>

> --
> Group jslibs - http://groups.google.com/group/jslibs - jsl...@googlegroups.com
> Unsubscribe: jslibs-un...@googlegroups.com

[Phil Rhodes]

> I can support integers from -9007199254740991 to +9007199254740991

Great!

I think that writeInt(n,8) should be supported, anyway, even if there's a
possible lack of precision.

P

[soubok]

FYI, The modification has been committed in the trunk.

[Phil Rhodes]

We're going to have to buy this guy a christmas present...

P

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08:02:00

[Phil Rhodes]

> FYI, The modification has been committed in the trunk.

Just out of interest - does this enable writing of ints of arbitrary length,
or just 8?

For instance, in wave files, any sample between 9 and 24 bits is packed into
a three-byte word - can I write three-byte words now?

P

[soubok]

On Wed, Dec 16, 2009 at 23:58, Phil Rhodes <phil_...@rocketmail.com> wrote:
>
>> FYI, The modification has been committed in the trunk.
>
> Just out of interest - does this enable writing of ints of arbitrary length,
> or just 8?

Currently I support 1,2,4,8 Bytes

>
> For instance, in wave files, any sample between 9 and 24 bits is packed into
> a three-byte word - can I write three-byte words now?

I will have a look at 3 bytes support.

[Phil Rhodes]

>> For instance, in wave files, any sample between 9 and 24 bits is packed
>> into
>> a three-byte word - can I write three-byte words now?
>
> I will have a look at 3 bytes support.

Sorry... I feel like I keep throwing jobs at you!

P