Re: NSLog with %f and comparisons using ==
Re: NSLog with %f and comparisons using ==
- Subject: Re: NSLog with %f and comparisons using ==
- From: James Maxwell <email@hidden>
- Date: Sat, 11 Apr 2009 13:45:50 -0700
hmm... Well, this all sounds like a sledge-hammer approach to my
immediate problem.
The actual explanation of what I'm doing is kind of long-winded, so
I'll spare you that. For now, I know the calculated values will always
come out the same, since there are a limited number of possible
inputs, and I know they'll very nearly match my stored constants (and
my constants are well separated, so is more than enough).
In future, I may want to handle a more continuous range of inputs, in
which case I'll have to look at the solutions you've provided, so I
appreciate your tips. Mind you, if that does become necessary, then
I'll probably have to approach the entire problem differently!
thanks,
J.
On 11-Apr-09, at 12:16 PM, Greg Guerin wrote:
James Maxwell wrote:
Now, when I run the calculation "live" and try to compare to my
stored constants, I'm not getting matches. I'm assuming this is
because the result of the calculation *isn't* actually what I
stored in my constants, since the constants were rounded during the
NSLog. So, how do I make sure my "live" calculation returns a value
that will be rounded in the same way as an NSLog(@"%f", aFloat)?
Maybe you're trying to solve the wrong problem.
Just because you have a constant float doesn't mean it has to be:
extern const float Foo;
It could also be:
#define Foo (Foo_Value())
extern float Foo_Value();
Then you run some initializing code that calculates your "constant"
values and stores them in static variables to be returned by the
functions. E.g.:
static float const_Foo;
extern float Foo_Value() { return const_Foo; }
extern void initializeConstants()
{ const_Foo = calc_Foo(); ..calculate and store other results.. }
You could use inline functions, too, if that's your thing.
Whether an approach like this is sufficient to avoid problems with
rounding error and precision loss, only you can say, because you
haven't explained anything about the actual calculations.
-- GG
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