Variable Substitution in darktable, Multiplication Possible?

Software darktable
1

I’d like to show the pixel count of the cropped image in Megapixels in the image information line, so I would like to do something such as

$(WIDTH.CROP*HEIGHT.CROP/1e6-$(WIDTH.RAW*HEIGHT.RAW/1e6))

instead of what I currently use:

$(WIDTH.CROP-$(WIDTH.RAW)):$(HEIGHT.CROP-$(HEIGHT.RAW))

Is this possible somehow? I cannot find it here: https://darktable-org.github.io/dtdocs/en/special-topics/variables/.

Edit:

Thinking more about it, I think this would not help, but I would need something such as

$(round(WIDTH.CROP*HEIGHT.CROP/1e6-$(WIDTH.RAW*HEIGHT.RAW/1e5)/10))

or fprint …