From: Martin <martin.dowie@btopenworld.com>
Subject: Re: How to put 200 into an integer sub-type of 16 bits (code included)
Date: Thu, 15 Jan 2009 00:57:17 -0800 (PST)
Date: 2009-01-15T00:57:17-08:00 [thread overview]
Message-ID: <00d83faa-26e5-4d7b-a36a-307ad699609a@v18g2000pro.googlegroups.com> (raw)
In-Reply-To: gkmmgp$aml$1@online.de
On Jan 15, 6:53 am, Michael Bode <m.g.b...@web.de> wrote:
> ChristopherL <clusard...@aol.com> writes:
> > The size of floating point number is 32 bits on my system, and my
> > float will
> > always be positive.
>
> > General information about floating point numbers in general:
>
> > Floating-point numbers are typically packed into a computer datum as
> > the sign bit, the exponent field, and the significand (mantissa).
>
> > Mantissa Exponent Value
> > 71 0 71
> > 71 1 710
> > 71 2 7100
> > 71 -1 7.1
> > 2 2 200
>
> > For example, it was shown above that π, rounded to 24 bits of
> > precision, has:
>
> > sign = 0 ; e = 1 ; s = 110010010000111111011011 (including the hidden
> > bit)
> > The sum of the exponent bias (127) and the exponent (1) is 128, so
> > this is represented in single precision format as
>
> > 0 10000000 10010010000111111011011 (excluding the hidden bit).
>
> > So, what is the proper way to store a number (never being greater
> > than
> > 200.5) in a 8 bit short number as outlined above?
>
> Try compressing it with gzip? Your question is how to store 4 bytes in
> 1 byte. The answer is, you don't. You use 4 8-bit numbers to store 1
> 32-bit number. In Ada you can do it like this:
>
> with Ada.Unchecked_Conversion;
> with Ada.Text_Io;
>
> procedure Convert is
> type SByte is range -128 .. 127;
> for SByte'Size use 8;
> type Float_Bytes is array (0 .. 3) of SByte;
>
> Arg : Float := 200.5;
> Result : Float_Bytes;
>
> function To_Bytes is new Ada.Unchecked_Conversion (Source => Float,
> Target => Float_Bytes);
> begin
> Result := To_Bytes (Arg);
> for I in Result'Range loop
> Ada.Text_Io.Put (Sbyte'Image (Result(I)) & " ");
> end loop;
> Ada.Text_Io.New_Line;
> end Convert;
>
> Output:
>
> 0 -128 72 67
For the insanely paranoid, you might want to add:
pragma Assert (Float'Size = 32);
next prev parent reply other threads:[~2009-01-15 8:57 UTC|newest]
Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <407ae64d-3cb3-4310-b59e-f1bbae9910a5@t39g2000prh.googlegroups.com>
2009-01-14 1:33 ` How to put 200 into an integer sub-type of 16 bits (code included) Brian Drummond
[not found] ` <3d3719f4-355c-4094-9902-495d612d46fe@n33g2000pri.googlegroups.com>
2009-01-14 9:06 ` Ludovic Brenta
2009-01-14 10:08 ` Georg Bauhaus
2009-01-14 10:29 ` Georg Bauhaus
2009-01-14 12:47 ` Brian Drummond
2009-01-14 12:53 ` Brian Drummond
[not found] ` <f4894476-851e-493f-93a2-168976bd97fb@s1g2000prg.googlegroups.com>
2009-01-14 16:08 ` Adam Beneschan
2009-01-14 21:17 ` sjw
[not found] ` <139961e9-bae6-4e60-8ff7-4f4779b27481@z6g2000pre.googlegroups.com>
2009-01-14 20:41 ` Adam Beneschan
[not found] ` <c265ffb7-6159-4d85-b259-78b830e115f9@v18g2000pro.googlegroups.com>
2009-01-15 2:39 ` SteveD@teranews.com
[not found] ` <3625f980-4406-4f51-b494-dd4a48cab840@p36g2000prp.googlegroups.com>
2009-01-15 6:53 ` Michael Bode
2009-01-15 8:57 ` Martin [this message]
[not found] ` <fc154f52-7168-447a-bcd3-6ece9066ebf7@r37g2000prr.googlegroups.com>
2009-01-15 10:29 ` Georg Bauhaus
[not found] ` <1a2b31ac-cf6b-44e3-85b7-04594460db87@d36g2000prf.googlegroups.com>
2009-01-14 22:47 ` Adam Beneschan
2009-01-14 23:11 ` Ludovic Brenta
2009-01-15 9:56 ` Stuart
2009-01-15 12:40 ` Stuart
2009-01-15 14:02 ` Stephen Leake
2009-01-15 15:54 ` Dmitry A. Kazakov
2009-01-15 16:29 ` Hyman Rosen
2009-01-15 22:15 ` Dmitry A. Kazakov
2009-01-16 9:11 ` Jacob Sparre Andersen
2009-01-16 11:03 ` Mike H
2009-01-16 22:16 ` Brian Drummond
2009-01-14 21:32 ` sjw
2009-01-14 21:51 ` Brian Drummond
2009-01-14 18:49 ` Jeffrey R. Carter
2009-01-15 10:12 ` Quote of the Day (Re: " Peter Hermann
2009-01-14 21:09 ` sjw
2009-01-14 21:16 ` Adam Beneschan
2009-01-14 23:09 ` Martin
2009-01-15 0:07 ` Adam Beneschan
2009-01-15 3:09 ` Randy Brukardt
2009-01-15 16:28 ` Adam Beneschan
2009-01-15 21:21 ` Robert A Duff
2009-01-16 1:17 ` Adam Beneschan
2009-01-16 14:55 ` Robert A Duff
2009-01-15 14:44 ` Brian Drummond
[not found] ` <3f1f2f67-5d69-4baf-8e8c-0d2b5f68475f@p36g2000prp.googlegroups.com>
2009-01-15 16:36 ` How to put 200.0 (is float variable of 32 bits) into an integer sub-type of 10 bits (complete program included) Adam Beneschan
[not found] ` <8e64f509-f6fe-4d86-ae1a-fe0b1c88555a@v5g2000pre.googlegroups.com>
2009-01-15 17:09 ` christoph.grein
2009-01-15 17:17 ` Adam Beneschan
2009-01-15 17:29 ` Georg Bauhaus
[not found] ` <09b4a056-688d-49c8-b935-fa0b30f1ae84@w1g2000prk.googlegroups.com>
2009-01-15 18:40 ` Mike H
[not found] ` <be26729d-9458-42fa-8c8c-004ca33b790d@f33g2000vbf.googlegroups.com>
2009-01-15 20:57 ` Niklas Holsti
[not found] ` <97231951-54a0-4df7-bb73-04261b34287f@e6g2000vbe.googlegroups.com>
2009-01-16 3:17 ` Steve D
[not found] ` <a61abb30-bc60-4d13-b298-f369ddc8f741@z6g2000pre.googlegroups.com>
2009-01-15 18:15 ` Martin
2009-01-15 18:34 ` Stuart
2009-01-15 17:23 ` Georg Bauhaus
[not found] ` <d3b7ad53-af51-4ac5-9167-7cb99e61b2b1@v5g2000pre.googlegroups.com>
2009-01-15 17:50 ` Stuart
[not found] <6c7964a6-1733-434b-b1b1-962baa4ebba2@p23g2000prp.googlegroups.com>
2009-01-13 21:01 ` How to put 200 into an integer sub-type of 16 bits (code included) Ludovic Brenta
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