Path: utzoo!attcan!uunet!lll-winken!ames!mailrus!cornell!uw-beaver!uw-june!uw-entropy!dataio!bright
From: bright@Data-IO.COM (Walter Bright)
Newsgroups: comp.lang.c
Subject: Re: Playing with the bits of floats
Message-ID: <1825@dataio.Data-IO.COM>
Date: 16 Jan 89 19:24:17 GMT
References: <MAX.89Jan13163256@george.lbl.gov>
Reply-To: bright@dataio.Data-IO.COM (Walter Bright)
Distribution: comp
Organization: Data I/O Corporation; Redmond, WA
Lines: 26

In article <MAX.89Jan13163256@george.lbl.gov> max@george.lbl.gov (Max Rible) writes:
>I'm trying to do deal with floating point numbers as if they're ints.
>Things like "if(((3.1 - 3.14) & 0x7FFFFFF) <= 0.1)"--- lousy
>programming style, I know, but I'm interested in speed, not
>portability for this application.

Two ways to do it:
	1. Define a union such as:
		typedef union
		{	double d;
			unsigned short u[4];
		} dblunion;
	   Assign values into d, and do the bit testing with u.
	2. Try this:
		double d;
		d = expression;
		if (*(unsigned short *)&d & 0x1234)
			...
I've generally used method 2. I know it violates all notions of
portability, but it was for very specific hardware! Using method
1 sometimes implies passing/returning unions to functions, which
is inefficiently implemented in a lot of compilers.

Unless your compiler supports something like (dblunion)(1.2) as
a 'type paint', I see no way to do this without going through a
memory location.