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From: mouse@mcgill-vision.UUCP (der Mouse)
Newsgroups: comp.lang.c
Subject: Re: C and Floating Point
Message-ID: <742@mcgill-vision.UUCP>
Date: Sun, 12-Apr-87 05:56:22 EST
Article-I.D.: mcgill-v.742
Posted: Sun Apr 12 05:56:22 1987
Date-Received: Sun, 19-Apr-87 10:19:48 EST
References: <15958@sun.uucp> <5716@brl-smoke.ARPA> <1283@dataio.Data-IO.COM>
Organization: McGill University, Montreal
Lines: 60
Keywords: C Fortran Floating Point

In article <1283@dataio.Data-IO.COM>, bright@dataio.Data-IO.COM (Walter Bright) writes:
> How about allowing numbers to be specified in binary radix, as in
> 0b00110101 ? [...] It seems odd that decimal, octal, hex, floating
> and ascii formats are supported, but not binary in a language
> supposedly designed for bit twiddling!

Good idea.  I've often wished for this.

> As a corollary, support %b in printf and scanf.

This will get dreadfully confusing.  At least in BSD UNIX, there is
already a %b in the kernel's version of printf; it is designed for
printing device register bits.  For example, this (hypotheical) error
message

hw3c: hard error sn12345: csr=402<IE,ERR> ers=1002<CRC,HARD>

might have been produced by (yes, I know it would really call
harderr(), be quiet, this is an example!) the following printf() call:

printf( "hw%d%c: hard error sn%d: csr=%b ers=%b\n",
	unit >> 3,
	"abcdefgh"[unit&7],
	blkno,
	hwdev->csr, "\10\2IE\3GO\5READY\11ERR",
	hwdev->ers, "\10\1SOFT\2HARD\4TIMEO\12CRC\13NODATA" );

> Also, support specifying floating numbers in hex radix. This would
> avoid horrible kludges like:

> [horrible kludge, using pointer punning]

> The syntax would be:
> 		double def = 0x1324.5E678e+0x12;
> 		double abc = -0x.1B4F;
> def prescribes a mantissa of 0x12345E678 and an exponent of
> (4*16+0x12).

> Note that a + or - would be required before the exponent, to
> distinguish the e from the digit e.

Not good enough.  "double def = 0x1234e+0x12" can be read as either
"mantissa 1234, exponent 4*16+0x12"
or
"value 0x12360" (sum of 0x1234e and 0x12).

> Such syntax would be very useful to those of us writing numerical
> subroutines. Numerical analysis books frequently give the constants
> to use specified in hex or octal, so as to control the resulting
> values exactly.

And if you are on a BCD machine, rather than a binary machine?  Or,
though I doubt any such actually exist, a ternary machine?

I guess there just aren't any good numerical algorithms for BCD or
ternary machines....:-)

					der Mouse

				(mouse@mcgill-vision.uucp)