From mboxrd@z Thu Jan  1 00:00:00 1970
To: 9fans@cse.psu.edu
Subject: Re: [9fans] fun and scary evil C code
From: "Russ Cox" <rsc@swtch.com>
Date: Wed, 19 Dec 2007 15:37:25 -0500
In-Reply-To: <3e1162e60712190715q3f50d601sd88b1e0c6c74afc8@mail.gmail.com>
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> #define TRIO_DOUBLE_INDEX(x) (((unsigned char *)&internalEndianMagic)[7-(x)])

this is actually done in /sys/src/9/port/devcons.c too:

	static uvlong uvorder = 0x0001020304050607ULL;
	
	static uchar*
	le2vlong(vlong *to, uchar *f)
	{
		uchar *t, *o;
		int i;
	
		t = (uchar*)to;
		o = (uchar*)&uvorder;
		for(i = 0; i < sizeof(vlong); i++)
			t[o[i]] = f[i];
		return f+sizeof(vlong);
	}
	
	static uchar*
	vlong2le(uchar *t, vlong from)
	{
		uchar *f, *o;
		int i;
	
		f = (uchar*)&from;
		o = (uchar*)&uvorder;
		for(i = 0; i < sizeof(vlong); i++)
			t[i] = f[o[i]];
		return t+sizeof(vlong);
	}

presotto wrote the code but said he learned the trick from ken.

there, of course, we have a real compiler and don't have to
write uvlong constants as floating point numbers
(wow that seems fragile).

russ