which code runs faster?

[nelu]

I know I can use unsinged byte, but I need it for java, which code runs
faster in C?

int f1(char b) {
return (b&0x80)|(b&0x7 f);
}

or

int f2(char b) {
return b>0?b:256+bl
}

?

In my tests f2 performs better. I need a better opinion. :-)
Thanks.

[Keith Thompson]

ro******@ibd.nr c-cnrc.gc.ca (Walter Roberson) writes:

In article <11************ **********@z14g 2000cwz.googleg roups.com>,
nelu <ta********@gma il.com> wrote:

Walter Roberson wrote:

Or, if it is known that CHAR_BIT is 8, then return (int)(unsigned char)b; Thus, the designer must decide whether the intent is to get at the
native bit pattern, or to get at the value "as if" it were 2s complement.

I was wondering which is the best way to get the value of a byte
between 0 and 255.

I guess the safest way is to use the if function for what I need since
bit operations can have different results in that form from machine to
machine, right?

Suppose, though, that CHAR_BIT is not 8. Imagine, for example, that
the "Windows" key operated by setting the 9th bit. How is your function
defined in such a case?

"byte" is a general concept, but the size of a "byte" varies
with different architectures. Same with "char". "byte" and "char"
are not exactly synonyms either.

No, they're not synonyms, but a "byte" is by definition the size of
type "char" in C. (Of course the terms are used differently outside
the context of C.)

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.

[Peter Nilsson]

nelu wrote:

Keith Thompson wrote:

No, they're not synonyms, but a "byte" is by definition the size of
type "char" in C. (Of course the terms are used differently outside
the context of C.)
In Java byte (8 bits) is the equivalent of signed char.

No. In C, signed char needn't be two's complement. You should be trying
to
use int8_t, rather than signed char.
char in java has 2 bytes.

I have never used a machine that has more or less than 8 bits in 1 byte
(not even on Sinclair Spectrum).
Some of the older PDP implementations had non-8-bit byte sizes.
Can you tell me how they work?
Like any other implementation, just with wider than usual bytes.
Is it possible for them to comunicate with 8 bits bytes machines and if yes,
how?

The same way that 8-bit byte machines communicate through 7-pin din
connectors.
Any number of ways. But none of them are necessarily topical in
comp.lang.c.

--
Peter

[nelu]

Peter Nilsson wrote:

No. In C, signed char needn't be two's complement. You should be trying
to
use int8_t, rather than signed char.

True, I was thinking about char the way I used it on my machine :-).

[nelu]

Keith Thompson wrote:

No, they're not synonyms, but a "byte" is by definition the size of
type "char" in C. (Of course the terms are used differently outside
the context of C.)

In Java byte (8 bits) is the equivalent of signed char. char in java
has 2 bytes.
I have never used a machine that has more or less than 8 bits in 1 byte
(not even on Sinclair Spectrum). Can you tell me how they work? Is it
possible for them to comunicate with 8 bits bytes machines and if yes,
how?

Thanks

[Mark McIntyre]

On 12 Dec 2005 15:09:08 -0800, in comp.lang.c , "nelu"
<ta********@gma il.com> wrote:

I was wondering which is the best way to get the value of a byte
between 0 and 255.

In C, a byte is the same size as a char. You get its value by
examining it. No casts are needed.

----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==----
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[Keith Thompson]

Mark McIntyre <ma**********@s pamcop.net> writes:

On 12 Dec 2005 15:09:08 -0800, in comp.lang.c , "nelu"
<ta********@gma il.com> wrote:

I was wondering which is the best way to get the value of a byte
between 0 and 255.

In C, a byte is the same size as a char. You get its value by
examining it. No casts are needed.

Unless it's a signed char (or a plain char and plain char happens to
be signed); then you can cast it to unsigned char.

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.

[Dave Thompson]

On 12 Dec 2005 20:22:02 -0800, "Peter Nilsson" <ai***@acay.com .au>
wrote:

nelu wrote:

<snip>

I have never used a machine that has more or less than 8 bits in 1 byte
(not even on Sinclair Spectrum).

Some of the older PDP implementations had non-8-bit byte sizes.

Terminology: this sounds like you mean different C implementations on
one "PDP" machine, or several "PDP" machines that implement a common
architecture. In fact Programmed Data Processor was the name used for
a series of machines by DEC (Digital Equipment Corporation) that were
mostly quite different, some with multiple implementations . There were
four models of PDP-10 namely KA-10, KI-10, KL-10, KS-10 which
implemented the same architecture, which was nearly the same as PDP-6.
There were several models of PDP-8 of which I recall 8/s, 8/i, 8/e,
8/m and 8/a, which implemented one architecture, nearly the same as
PDP-5 and similar to PDP-12 aka LINC-12, but very different from -6
and -10. PDP-7 and -9 were similar, and I believe also similar to -4
and -1, but different from -6/10 and -5/8/12. There were many
(numbered) models of PDP-11 like 11/20, 11/40, 11/45, 11/34, 11/70
etc. all implementing basically the same architecture, different from
all other PDP series machines.

There were also quite a few non-DEC machines with non-8-bit bytes.

Can you tell me how they work?

Like any other implementation, just with wider than usual bytes.

Is it possible for them to comunicate with 8 bits bytes machines and if yes,
how?

The same way that 8-bit byte machines communicate through 7-pin din
connectors.
Any number of ways. But none of them are necessarily topical in
comp.lang.c.

In the early days of the Internet and before that ARPANET, this was a
significant issue and there are a number of features (still) specified
especially in FTP to deal with data exchange with systems having a
byte other than 8 bits, no longer used today except perhaps
occasionally by mistake.

- David.Thompson1 at worldnet.att.ne t