From: tmoran@bix.com
Subject: Re: Newbie question : types , representation
Date: 1999/08/27
Date: 1999-08-27T00:00:00+00:00 [thread overview]
Message-ID: <5oAx3.5359$W5.510061@typhoon-sf.snfc21.pbi.net> (raw)
In-Reply-To: 37C621F3.C6C0DC3A@acenet.com.au
> In base64 decoding , each ASCII character must be translated to 6 'bit'.
> 4 characters translate then to 3 bytes. The problem and algorithms are
> trivial. In C I could do it within 5 minutes.
Given modern RAM sizes, how about the initally mentioned table lookup
type Base64 is range 0 .. 63;
type Base64_String is array(integer range <>) of Base64;
subtype Base64_Quad is Base64_String(1 .. 4);
type Byte is range 0 .. 255;
type Byte_String is array(integer range <>) of Byte;
subtype Byte_Triple is Byte_String(1 .. 3);
To_Base64 : array(Byte, Byte, Byte) of Base64_Quad;
From_Base64 : array(Base64, Base64, Base64, Base64) of Byte_Triple;
-- initialize the arrays once, at start time
-- timing test
data: Base64_String(1 .. 200);
result : Byte_String(1 .. 150);
si,di : positive;
begin
for i in 1 .. 100_000 loop
si := 1;
di := 1;
for j in 1 .. data'length/4 loop
result(di .. di+2) := From_Base64(Data(si), Data(si+1),
Data(si+2), Data(si+3));
di := di+3;
si := si+4;
end loop;
end loop;
On my P200, this sort of thing executes at a rate of about 6 Base64
characters, or 4 Byte's, converted each microsecond. Using a
modern fast CPU you would approach being I/O bound.
next prev parent reply other threads:[~1999-08-27 0:00 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
1999-08-22 0:00 Newbie question : types , representation Jos De Laender
1999-08-22 0:00 ` Wilhelm Spickermann
1999-08-23 0:00 ` Martin C. Carlisle
1999-08-23 0:00 ` Simon Wright
1999-08-22 0:00 ` Robert Dewar
1999-08-23 0:00 ` Wolfgang Jeltsch
1999-08-24 0:00 ` tmoran
1999-08-24 0:00 ` jdla
1999-08-24 0:00 ` Matthew Heaney
1999-08-24 0:00 ` Jos De Laender
1999-08-24 0:00 ` Brian Rogoff
1999-08-25 0:00 ` Jos De Laender
1999-08-22 0:00 ` Martin Dowie
[not found] ` <37C621F3.C6C0DC3A@acenet.com.au>
1999-08-27 0:00 ` tmoran [this message]
1999-08-27 0:00 ` Florian Weimer
1999-08-27 0:00 ` David C. Hoos, Sr.
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