I'm still a beginner at programming and I always have more questions than our book or internet searches can answer (unless I missed something). So I apologize in advance if this was answered but I couldn't find it.
I understand that float has a smaller range than double making it less precise, and from what I understand, long double is even more precise(?). So my question is why would you want to use a variable that is less precise in the first place? Does it have something to do with different platforms, different OS versions, different compilers? Or are there specific moments in programming where its strategically more advantageous to use a float over a double/long double?
Thanks everyone!
A float uses less memory than a double, so if you don't need your number to be the size of a double, you might as well use a float since it will take up less memory. Just like you wouldn't use a bus to drive yourself and a friend to the beach... you would be far better off going in a 2 seater car.
They have different sizes and precision. Basically all of them represent the decimal values such as 3.14 The main difference between them is that in float we can store values upto 4 bytes (6 places after decimal point) Double upto 8 bytes And long double even more than float and double.
The type double provides at least as much precision as float, and the type long double provides at least as much precision as double. The set of values of the type float is a subset of the set of values of the type double; the set of values of the type double is a subset of the set of values of the type long double.
Integers and floats are two different kinds of numerical data. An integer (more commonly called an int) is a number without a decimal point. A float is a floating-point number, which means it is a number that has a decimal place. Floats are used when more precision is needed.
In nearly all processors, "smaller" floating point numbers take the same or less clock-cycles in execution. Sometimes the difference isn't very big (or nothing), other times it can be literally twice the number of cycles for double
vs. float
.
Of course, memory foot-print, which is affecting cache-usage, will also be a factor. float
takes half the size of double
, and long double
is bigger yet.
Edit: Another side-effect of smaller size is that the processor's SIMD extensions (3DNow!, SSE, AVX in x86, and similar extensions are available in several other architectures) may either only work with float
, or can take twice as many float
vs. double
(and as far as I know, no SIMD instructions are available for long double
in any processor). So this may improve performance if float
is used vs. double
, by processing twice as much data in one go. End edit.
So, assuming 6-7 digits of precision is good enough for what you need, and the range of +/-10+/-38 is sufficient, then float
should be used. If you need either more digits in the number, or a bigger range, move to double
, and if that's not good enough, use long double
. But for most things, double
should be perfectly adequate.
Obviously, the importance of using "the right size" becomes more important when you have either lots of calculations, or lots of data to work with - if there are 5 variables, and you just use each a couple of times in a program that does a million other things, who cares? If you are doing fluid dynamics calculations for how well a Formula 1 car is doing at 200 mph, then you probably have several tens of million datapoints to calculate, and every data point needs to be calculated dozens of times per second of the cars travel, then using up just a few clockcycles extra in each calculation will make the whole simulation take noticeably longer.
There are two costs to using float, the obvious one of its limited range and precision, and, less obviously, the more difficult analysis those limitations impose.
It is often relatively easy to determine that double is sufficient, even in cases where it would take significant numerical analysis effort to show that float is sufficient. That saves development cost, and risk of incorrect results if the more difficult analysis is not done correctly.
Float's biggest advantage on many processors is its reduced memory footprint. That translates into more numbers per cache line, and more memory bandwidth in terms of numbers transferred per second. Any gain in compute performance is usually relatively slight - indeed, popular processors do all floating point arithmetic in one format that is wider than double.
It seems best to use double unless two conditions are met - there are enough numbers for their memory footprint to be a significant performance issue, and the developers can show that float is precise enough.
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