Difference between revisions of "Category:LSL Float"

If you need to validate an arbitrary float without limitations then the following function is ideal:

integer isValidFloat(string s) { return (string)((float)s) != (string)((float)("-" + llStringTrim(s, STRING_TRIM_HEAD))); }

However, the following is more efficient, but comes with the noted caveats. If these are not an issue to you then it is the recommended option, particularly under Mono:

integer isValidFloat(string s) { return (float)(s + "1") != 0.0; }

Caveats:

• LSO-LSL scientific notation with an exponent greater than 38 will fail (throw a Math Error). Mono is unaffected as it supports infinity
• Under both Mono and LSO-LSL you may find strange results if dealing with strings containing more than 9 decimal places. Remember that string casting in LSL only gives up to 6 so is safe, and human input is rarely going to be that accurate, plus values that small are not usually all that useful.
• Due to the limited precision with which floats are stored, not all integer values can be accurately held in a float: only the values between -16,777,216 and 16,777,216 are precise. Between +/-16,777,216 and +/-33,554,432 values are rounded to even numbers, beyond +/-33,544,432 they are rounded to multiples of 4, etc. The rounding is towards the nearest value, or towards zero if both are equally far.
• "nan" (not-a-number), "inf" (infinity) and their negatives are special text values that can be cast from a string (with any leading spaces or trailing characters). those values will cause a math error when the variable is evaluated in LSO. If you are parsing user data, by casting a string to a float, use the following code (replacing vStrDta with your string variable name) see SVC-6847:

  (float)llList2String( llParseStringKeepNulls( llToLower( llStringTrim( vStrDta, STRING_TRIM ) ), ["inf", "nan"], [] ), 0 )
  

However, both of the above snippets will stop validating at the first character that is not valid in a float string. The following code rigorously validates the whole of a string to ensure it represents a float (and nothing else), at the cost of speed and memory footprint.

// Validate a string containing a float value
// Does not handle scientific notation, or hex floats (!!)
// After all, this is designed for 95% of likely human entered data

integer  ValidateSimpleFloat(string sin)
{
    sin = llToLower(sin);
    // Avoid run time fail (for lslEditor at least) if string looks remotely like scientific notation 
    if (llSubStringIndex(sin, "e") != -1)   	return FALSE; 	
    list temp = llParseStringKeepNulls(sin, ["."], [] );
    string subs = llList2String(temp, 0);
    if ( (string) ( (integer) subs) != subs)    return FALSE;
    if ( (temp != []) > 2)                      return FALSE;
    if ( (temp != [])== 2)
    {
	subs = llList2String(temp, 1);    // extract the decimal part
        // must have no sign after DP, so handle first decimal discretely
	string first = llGetSubString(subs, 0, 0);
	if ( (string) ( (integer) first) != first)     return FALSE;  
	if ( (string) ( (integer) subs)  != subs)      return FALSE;
    }
    return TRUE;
}

There are several ways to convert a float to a string. The first of which is to typecast it to a string (string)(1.0). This however has the disadvantage of rounding and being limited to six decimal places. Several functions have been written to provide more options. They fall into two categories, lossless and lossy.

• Infinity is only accessible in Mono.