R
ravi
Give a one-line C expression to test whether a number is a power of 2.
[No loops allowed]
[No loops allowed]
M
Martin Ambuhl
No, and why are you giving orders?ravi said:
D
Default User
ravi said:
Do your own homework.
Brian
C
CBFalconer
ravi said:
For unsigned integers:
if (!((n - 1) & n)) puts("n is power of 2");
R
ravi
Beacuse I am your father
E
Erik de Castro Lopo
ravi said:
static inline int
is_power_of_2 (int x)
{
return ((x & (x - 1)) == 0) ;
}
--
R
Richard Heathfield
Erik de Castro Lopo said:
Having proved willing to do homework for free, you and Chuck might want
to brace yourselves for the rush.
Having proved willing to do homework for free, you and Chuck might want
to brace yourselves for the rush.
S
santosh
ravi said:
Most participants of this group an, (not unreasonable), expectation of
people who post homework questions to have at least made an honest
attempt at the problem. This group hosts, perhaps, the best minds in C
you're likely to meet, but you, (as a new participant and a learner),
need to show willingness to put in some effort on your part, (like
trying to remain civil), to get the best response and help. At least
that been my experience in my participation in this group.
A
Army1987
What if x <= 0 (in which case x cannot be a power of two)?
P
pete
C
CBFalconer
Richard said:
I like my version better
In all seriousness, this is not sucha simple thing, so I doubt it was homework. If he hadn't used such
rude terminology I would be virtually sure it is not.
E
Eric Sosman
ravi said:
That explains my congenital idiocy.
P
pete
F
Flash Gordon
Eric Sosman wrote, On 08/07/07 13:27:
Probably. Had you enough sense you would have instantly known the answer
was:
int powerof2( double num ) { return 1; }
After all, the OP did not specify integer power of 2, or even real power
of 2, and I think if you allow complex powers, all numbers will qualify.
Probably. Had you enough sense you would have instantly known the answer
was:
int powerof2( double num ) { return 1; }
After all, the OP did not specify integer power of 2, or even real power
of 2, and I think if you allow complex powers, all numbers will qualify.
H
Harald van =?UTF-8?B?RMSzaw==?=
Flash said:
What about zeroes, infinities, and NaNs? I would think it should return 0
for those.
F
Flash Gordon
Harald van Dijk wrote, On 08/07/07 23:37:
Zero is easy to deal with, infinities could be argued as being powers of
2, and change the input parameter to an integer type to get rid of the
problem of NaNs Alternatively, in C99 you can use isnan and isinf to
solve the problem.
int powerof2(double num) {return !(isnan(num) || isinf(num) || num==0)}
There is, of course, the question of whether you want to count numbers
that are almost zero as zero because of rounding, but I'll leave dealing
with that as an exercise to anyone wanting that functionality.
Zero is easy to deal with, infinities could be argued as being powers of
2, and change the input parameter to an integer type to get rid of the
problem of NaNs
Alternatively, in C99 you can use isnan and isinf to solve the problem.
int powerof2(double num) {return !(isnan(num) || isinf(num) || num==0)}
There is, of course, the question of whether you want to count numbers
that are almost zero as zero because of rounding, but I'll leave dealing
with that as an exercise to anyone wanting that functionality.
C
Christopher Benson-Manica
[OP wrote:]
Given the number of ridiculous questions that are routinely asked here
that clearly *are* homework, I'm surprised you find it unlikely that
the above question is not homework. Why else would there be
constraints such as "one line" or "no loops allowed" (snipped from
above context)? I personally find it highly unlikely that anyone
asking the question seriously would phrase it so tersely.
I like my version better
a simple thing, so I doubt it was homework. If he hadn't used such
rude terminology I would be virtually sure it is not.
Given the number of ridiculous questions that are routinely asked here
that clearly *are* homework, I'm surprised you find it unlikely that
the above question is not homework. Why else would there be
constraints such as "one line" or "no loops allowed" (snipped from
above context)? I personally find it highly unlikely that anyone
asking the question seriously would phrase it so tersely.
C
CBFalconer
Christopher said:
You have a definite point, and are probably right.
W
websnarf
Oh for crying out loud! The other answers had the OP perfectly set up
with the wrong answer (brilliant coordination, BTW, guys -- all of you
getting it simultaneously wrong in exactly the same way). Now the OP
can figure it out completely correctly without any research himself.
Good job.
N
Nick Keighley
ah, but the spec said test a *number* and I don't think infinity is a
number and as for NaN...
So it should indicate some sort of domain error or assert on a debug
build.