On Fri, 2001-09-14 at 15:42, Dan Sugalski wrote:
> At 03:10 PM 9/14/2001 -0500, Brian Wheeler wrote:
> >I've been thinking alot about the bytecode file format lately. Its
> >going to get really gross really fast when we start adding other
> >(optional) sections to the code.
> >
> >So, with that in mind, here's what I propose:
> >
> >* All data sizes are in longwords (4 bytes) because that's just the way
> >things are :)
>
> Nope. At the very least, a bytecode file needs to start with:
>
> 8-byte word: endianness (magic value 0x123456789abcdef0)
> byte: word size
> byte[7]: empty
> word: major version
> word: minor version
>
> Where all word values are as big as the word size says they are.
>
> The magic value can be something else, but it should byteswap such that if
> you read it in you can tell whether it was a big-endian write or a
> little-endian write.
>
> Followed by the offsets to the various segments in the file. The directory
> (basically the offsets) *must* be at the very beginning, right after the
> header.
>
> Also, don't choose a stream format that makes writing the file easy--choose
> one that makes reading easy and fast. Two or three passes before writing
> are fine.
>
And...in another message....
> Heh. Doing our bytecode files in IFF format would be really nifty. We
> could even see about raiding the old Fred Fish library for C source to
> read and write 'em... :)
Fred Fish...that's a name I've not heard in a long time. I still have a
floppy or two with "fish disk ###" stuck on them.
Ok, I'll admit I was initially considering IFF but it seemed too
scary...but then it could be residual feelings from when I was a
youngster and tried to write them with BASIC :)
Ok, what if we did IFF with these caveats:
* all chunks must be padded to 4 bytes (instead of IFF's 2)
* no nesting of FORMs
Chunks we'd need are:
Name: 'PINF' - Parrot Information
Size: 28 bytes + size of directory
Optional: No
Data:
long magic cookie (or will PINF) be enough?
8-byte word: endianness (magic value 0x123456789abcdef0)
byte: word size
byte[7]: empty
word: major version
word: minor version
long count of directory entries
--- directory goes here ---
-- each entry as follows --
long type of chunk
long offset
Name: 'PBYT' - Parrot Bytecode
Size: Varies
Optional: Sure. :)
Data:
bytes of the bytecode
Name: 'PSTR' - Parrot String Table
Size: Varies
Optional: Yes
Data:
long Count of string entries
--- each string as follows ---
long byte length
n bytes + pad string data
Name: 'PFIX' - Parrot Fixup Table
Size: Varies
Optional: Yes
Data:
--- beats me...how are we doing fixups? ---
Name: 'PNOT' - Parrot Notes Block
Size: Varies
Optional: Yes
Data:
free-form text for 'notes' about the file.
How's this?
Brian
