how to use AtomiccmpExchange with double?

I have a double value that I need to access to inside a backgroundThread. I would like to use somethink like AtomiccmpExchange but seam to not work with double. is their any other equivalent that I can use with double ? I would like to avoid to use Tmonitor.enter / Tmonitor.exit as I need something the most fast as possible. I m under android/ios so under firemonkey

Solution

You could type cast the double values into UInt64 values:

PUInt64(@dOld)^ := AtomicCmpExchange(PUInt64(@d)^,PUInt64(@dNew)^,PUInt64(@dCom‌p)^);

Note that you need to align the variables properly, according to platforms specifications.

As @David pointed out, comparing doublevalues is not the same as comparing UInt64 values. There are some specific double values that will behave out of the ordinary:

A NaN is normally (as specified in IEEE-754) detected by comparing a value by itself.
```
IsNaN := d <> d; 
```
footnote: Delphi default exception handler is triggered in the event of comparing a NaN, but other compilers may behave differently. In Delphi there is an IsNaN() function to use instead.
Likewise the value zero could be both positive and negative, for a special meaning. Comparing double 0 with double -0 will return true, but comparing the memory footprint will return false.