The actual arithmetic (floating point) was not too much of a problem, the challenge was converting the result to hex. I managed to find a bit of code on the web which did the job a treat.

https://stackoverflow.com/questions/5301034/how-to-generate-random-64-bit-value-as-decimal-string-in-php/5302533#5302533

(Section 2 of the above link.)

Excellent response. Thank you. I found that the digits to the right of the decimal point in the value returned from Getdifficulty can safely be ignored.

Now, once I have figured how to handle the very large numbers in PHP I should be in good shape.

Thanks for the quick reply. A problem I have is how to interpret the number returned, for example

4306949573981.513

What does the period represent? Is it simply a decimal point? If so, do I ignore the digits to the right of the decimal point when converting the number to hex?

Does the period represent a floating point number?

I am using Bitcoin Core 64-bit, 0.16.0 (on Windows 7) and I am playing around with PHP to access Bitcoin client with RPC.

It's all going quite well but I have hit a bit of a roadblock trying to process Difficulty.

The "GetDifficulty" RPC call returns a value like

4306949573981.513

How do I transform this value into an actual target like 0x1b0404cb ?