[YZF]

Yeah, there was a C compiler, a Pascal compiler... I'm pretty sure others. I would guess at least 100x for an optimized assembly version. Even 500x between this sort of interpreter and assembly is not unheard of.

[lproven]

And a BASIC compiler.

https://spectrumcomputing.co.uk/entry/8249/ZX-Spectrum/HiSof...

The manual:

http://hayne.net/Spectrum/HiSoftBASIC/manual.html

[YZF]

HiSoft... that does bring back some memories.