From: nobu.nokada@...
Date: 2003-05-29T08:37:11+09:00
Subject: Re: RCR: unpack/pack Bignum

Hi,

At Thu, 29 May 2003 07:20:04 +0900,
Robert Feldt wrote:
> No one seems to be interested in this issue so I'll have to reply to
> myself... ;)

I've thought about same thing (and Bignum constructor from
binary data), but not found good template characters for them.

> It should work for both big and little endian architectures but I've only
> tried on little endian. Would be great if someone can try on big-endian
> machine.
> 
> This patch adds a 'W' template character to pack and unpack for
> packing/unpacking an unsigned integer (Fixnum *OR* Bignum). The packing
> is from MSB to LSB so that
> 
>  [0xff00].pack("W") == "\377\000"

I guess Bignum (un)packing would be used for external data
exchange, so it'd be better to provide each singned/unsigned
and big/little endian conversion, like as 'l', 'L' and so on.
But 'w' is used already.

> I choose W as in "raW binary representation of number" but its hard to
> find a good template char since most are taken.

Agree.

A nitpicking:
> -                len = RBIGNUM(from)->len * SIZEOF_BDIGITS;
> -                {
> -		    char tmp[len];
> -
> -                    rb_nonneg_bignum_pack(tmp, from);
> -		    // Skip leading zeroes if positive bignum. Extend
> -		    // this "strategy" for 'w' so that only negative
> -		    // bignums (and 0) can have leading zero?

Variable length array and C++ style comment are C99 feature (or
a compiler's extension).

-- 
Nobu Nakada