LSL Wiki : float

Float

A float is an IEEE-754 32-bit floating point value ranging from ±1.401298464E-45 to ±3.402823466E+38.

Examples:

9.9
10.0
100000.1

LSL floats can be specified in scientific notation, e.g. 1.123E-2 or 512E+3.

Additionally, the letter f or F can be appended. This is a relic from C, where the f is needed to specify for the compiler that it is a float and not a double (LSL only uses floats).

A 32-bit float is divided into a 24-bit signed "mantissa" (containing the actual significant digits) and an 8-bit signed "exponent" (representing the magnitude that the mantissa will be multiplied with). A 23-bit (1 bit lost for sign) mantissa gives a precision equivalent to approximately 7 decimal digits (more exactly log₁₀(2²³)). This means values are rarely exactly stored and, often more disturbingly, addition or subtraction of two numbers of vastly different magnitudes might yield unexpected results, as the mantissa can't hold all the significant digits.

As per IEEE-754, LSL supports negative zero, there is currently no way of detecting negative zero, except by typecasting to a string .

Example:
340000000.0 + 4.0 = 340000000.0
The correct answer (340000004.0) has 9 significant digits, thus the last two digits are lost.

Some functions have tooltips within the LSL editor that say "F32", indicating a 32-bit float, rather than simply "float". However, all floats in LSL are 32-bit. So if it says "F32", it may be read as just "float".

Certain things are picky about whether they are passed a float or an integer. -To make an integer into a float, add .0 to the end. Other functions don't require this, and so the joys of non-uniform functions can be experienced. However, it is necessary to explicitly cast a float to an integer, since precision is lost.

There are 4 techniques for converting a float to an integer.

Function Name	Purpose
`(integer)`	Returns the integer portion of the float, ignoring the decimal.
`llRound`	Rounds float around 1/2 (1.2 rounds to 1, 1.6 rounds to 2, -2.5 rounds to -3).
`llCeil`	Rounds float up to an integer, partially equivelent to typecast.
`llFloor`	Rounds down to an integer, partially equivelent to typecast.

Note: using the typecast equivalent, if available, is going to be faster and use less memory.

Note Details: If speed is a concern (integer) should always be used.
Typecasting uses slightly less memory(10-20b)

Function Name	Slower	Sign	Code
`llFloor`	50%	+	(integer)float
`llRound`	30%	-	(integer)(float - 0.5)
`llRound`	30%	+	(integer)(float + 0.5)
`llCeil`	50%	-	(integer)float

If you wish to typecast a float to a string whilst omitting the trailing zeroes (and dot if it is actually an integer value), this code may help you:

string float2string(float input) {
    string result=(string)input;
    integer i=llStringLength(result);
    while(llGetSubString(result,--i,i)=="0");
    result = llDeleteSubString(result,i+1,llStringLength(result));
    integer dot = llStringLength(result)-1;
    if(llGetSubString(result,dot,dot) == ".") result = llDeleteSubString(result,dot,dot);
    return result;
}

For the interested reader, there is a good article about the floating standard:
What Every Computer Scientist Should Know About Floating-Point Arithmetic
So before you compain about problems with floats at least read the first few pages of the article :P

Q: Is there a non-lossy way to convert a float to a string and then back to a float again so that the resulting float has the same value as the original float?
A: I am not fully sure, but I strongly suspect not since I seem to remember IEEE floats use base 2 for the mantissa (and exponent), which cannot be losslessly converted to base 10 that the string would display, meaning truly binary-equivalent conversion to string (and therefore communication via strings) would be impossible. Someone please double-check this. (The same would go for the equivalent questions in vector and rotation, and if true, this answer should probably go here, not three places.) -?
AA: While the answer to this question is closely related to the answers to the equivalent questions on the vector and rotation pages, the technique used to "serialize" vectors and rotations would be more involved at the very least including some method of dismantling them into their component floats. I think this FAQ is useful on the vector and rotation pages independent of its presence on this page. -GordonPrior

I will go ahead and make a serialization page. Mono will probably obsolete any hacks we come up with to accomplish serialization in LSL but then again Mono will obsolete most of the pages on this wiki. -?

Q: What is a NaN?
A: See NaN.

Types | Binary | Memory Usages