Corner cases - Manual - SIMATIC AX - System.FastMath - System.FastMath,

For this function, different behaviors occur between the targets 1500 and llvm in certain corner cases:

Operand	Result 1500	Result llvm	Description
Positive subnormal number	0.0	Square root of operand
Signaling NaN	Signaling NaN	Quiet NaN	1500 returns the operand as result. llvm also, except that the most significant bit of mantissa is set to 1 to indicate qNaN.

Notes

A subnormal number is also called a denormalized number, see IEEE 754. In ST, this means

• a REAL number with an absolute value smaller than 1.1754944E-38,
• or an LREAL number with an absolute value smaller than 2.22507385850720138309023271733E-308.

For definitions and using recommendations of signaling NaN and quite NaN, also see IEEE 754.

In case identical behaviors of both targets are needed for these corner cases, System.FastMath.Sqrt() might not be suitable. Use System.Math.Sqrt() instead, which has worse runtime performance but gives identical results for both targets.