Converting a hexidecimal string to a floating point array

[Bushido Hacks]

Hey c.l.c++ and/or c.g.a.opengl posters,

How do I convert a hexidecimal string, traditionally used for defining
colors with HTML, into a floating point array?

In other words, how do I convert this:
char* hex = "#FF9933";

into this:

float fpa = { 1.0, 0.6, 0.2 };

[Victor Bazarov]

Bushido Hacks wrote:

Hey c.l.c++ and/or c.g.a.opengl posters,

How do I convert a hexidecimal string, traditionally used for defining
colors with HTML, into a floating point array?

In other words, how do I convert this:
char* hex = "#FF9933";

into this:

float fpa = { 1.0, 0.6, 0.2 };

Skip the #, extract the first two hex digits and convert it to
an integer from base-16 string using strtol, divide the integer
by 255. (double constant, don't forget the dot). Then repeat
for the other two pairs of hex digits. Wrap it up in a function
and you get yourself something you can use over and over. Or
you could do it without extracting digits. Just convert the
entire number into a long, then split it into three integers
using / and %, then do the division by 255. like before.

V

[Wolfgang Draxinger]

Victor Bazarov wrote:

using / and %, then do the division by 255. like before.

division and module are expensive. Better is bitwise masking and
bitshifting. It's strange but I've seen a lot of programs using
division and module for operaions that would have been better
done with bitwise operations. Is there a certain reason other
than ignorance?

Wolfgang Draxinger
--

[abecedarian]

Wolfgang Draxinger wrote:

Victor Bazarov wrote:

using / and %, then do the division by 255. like before.

division and module are expensive. Better is bitwise masking and
bitshifting. It's strange but I've seen a lot of programs using
division and module for operaions that would have been better
done with bitwise operations. Is there a certain reason other
than ignorance?

Hear, hear! A real expert speaking!

[JB West]

"Victor Bazarov" <v.********@com Acast.net> wrote in message
news:ed******** ************@co mcast.com...

Bushido Hacks wrote:

Hey c.l.c++ and/or c.g.a.opengl posters,

How do I convert a hexidecimal string, traditionally used for defining
colors with HTML, into a floating point array?

In other words, how do I convert this:
char* hex = "#FF9933";

into this:

float fpa = { 1.0, 0.6, 0.2 };

Skip the #, extract the first two hex digits and convert it to
an integer from base-16 string using strtol, divide the integer
by 255. (double constant, don't forget the dot). Then repeat
for the other two pairs of hex digits. Wrap it up in a function
and you get yourself something you can use over and over. Or
you could do it without extracting digits. Just convert the
entire number into a long, then split it into three integers
using / and %, then do the division by 255. like before.

V

If you are using as a color argument, you may not need to convert to float.
Just parse & pass to OpenGL. void glColor3us( GLushort red, GLushort green,
GLushort blue )
-jbw

[Victor Bazarov]

Wolfgang Draxinger wrote:

Victor Bazarov wrote:

using / and %, then do the division by 255. like before.

division and module are expensive. Better is bitwise masking and
bitshifting. It's strange but I've seen a lot of programs using
division and module for operaions that would have been better
done with bitwise operations. Is there a certain reason other
than ignorance?

For 255 (256) there probably isn't. For other values there may
not be a simple solution using bit shifts and masks.

[Peter Koch Larsen]

"Wolfgang Draxinger" <wd********@dar kstargames.de> skrev i en meddelelse
news:91******** ****@darkstarga mes.dnsalias.ne t...

Victor Bazarov wrote:

using / and %, then do the division by 255. like before.
division and module are expensive. Better is bitwise masking and
bitshifting. It's strange but I've seen a lot of programs using
division and module for operaions that would have been better
done with bitwise operations. Is there a certain reason other
than ignorance?

Well, if you divide i by 128 what expression looks best?

i/128 -or- 1 >> 7 ?

The naïve programmer might prefer the first one, but any expert hacker would
naturally prefer option number 2.

The only problem is that the second option is non-portable whereas the first
is fine - and just as fast on any compiler i've encountered the last 15
years.
So take your poison. Are you a hacker or just a naïve programmer like me?

/Peter

Wolfgang Draxinger
--

[Bushido Hacks]

Gee people. Come'on! IT'S A SIMPLE QUESTION. Im not interested in
doing all this goofy crap right now. I just want to use a simple
straightforward method. I'm not trying to hack the Pentagon.

I want an answer that only uses char, int, double, or float. Not long.
Not short. Not string. And certainly nothing to do with C or Assembly,
or Visual whatever. Just regular ISO standard C++. That's all.

Man. You know what our problem is, we just take thing too literally.
Where as you guys take a ten page list of codes, I could probably
factor into about a page and a half.

And since when did division and mod become expensive operations? I
doubt any of that is true. If they are, why bother using +, -, *, !,
&&, ||, &, |, <, >, == , or even = ?

My only interest in this is to just make a simple OpenGL model using
C++.

I just want to break the string apart into characters. First character
divsible by FF (255) and the second character divsable by F (15) then
add the two digits and assign them to an array of size 3.

But my first road block is to break apart the string. Remember, I want
to use a STRING not an actual hexidecimal.

[Alvin]

Bushido Hacks wrote:

Gee people. Come'on! IT'S A SIMPLE QUESTION. Im not interested in
doing all this goofy crap right now. I just want to use a simple
straightforward method. I'm not trying to hack the Pentagon.

I want an answer that only uses char, int, double, or float. Not long.
Not short. Not string. And certainly nothing to do with C or Assembly,
or Visual whatever. Just regular ISO standard C++. That's all.

Man. You know what our problem is, we just take thing too literally.
Where as you guys take a ten page list of codes, I could probably
factor into about a page and a half.

And since when did division and mod become expensive operations? I
doubt any of that is true. If they are, why bother using +, -, *, !,
&&, ||, &, |, <, >, == , or even = ?

My only interest in this is to just make a simple OpenGL model using
C++.

I just want to break the string apart into characters. First character
divsible by FF (255) and the second character divsable by F (15) then
add the two digits and assign them to an array of size 3.

But my first road block is to break apart the string. Remember, I want
to use a STRING not an actual hexidecimal.

The answer has been given. Ignore the #. Read two chars from the string.
Convert those chars into a single number (in base-16...this is important).
Then divide that number by 255. Then convert the resulting number (it will
be a decimal number between 0 and 1) into it's string equivalent.

Alvin

[Peter Koch Larsen]

"Bushido Hacks" <bu**********@g mail.com> skrev i en meddelelse
news:11******** **************@ z14g2000cwz.goo glegroups.com.. .

Gee people. Come'on! IT'S A SIMPLE QUESTION. Im not interested in
doing all this goofy crap right now. I just want to use a simple
straightforward method. I'm not trying to hack the Pentagon.

I want an answer that only uses char, int, double, or float. Not long.
Not short. Not string. And certainly nothing to do with C or Assembly,
or Visual whatever. Just regular ISO standard C++. That's all.

Man. You know what our problem is, we just take thing too literally.
Where as you guys take a ten page list of codes, I could probably
factor into about a page and a half.

And since when did division and mod become expensive operations? I
doubt any of that is true. If they are, why bother using +, -, *, !,
&&, ||, &, |, <, >, == , or even = ?

My only interest in this is to just make a simple OpenGL model using
C++.

I just want to break the string apart into characters. First character
divsible by FF (255) and the second character divsable by F (15) then
add the two digits and assign them to an array of size 3.

But my first road block is to break apart the string. Remember, I want
to use a STRING not an actual hexidecimal.

That question was answered in Victor Bazarovs reply - so why this post?

/Peter