1 Nov
2004
1 Nov
'04
12:37 p.m.
(Ted Harding) Ted.Harding@nessie.mcc.ac.uk writes:
But I'd first learned the chip on the Sinclair ZX-81, actually disassembling the ROM by hand with pencil and paper (and the Z80 ref manual to hand). Incidentally, the ZX-81 stored numbers, and did arithmetic on them, in a very strange format. Not BCD at all, and not straight binary floats either, but binary floats with weird extras. I never worked out why they did it that way.
I believe it used the same mechanism as the Spectrum, which used binary floating point with a one byte exponent and a 4 byte mantissa, but could also represent integers in [-65535,65535] as straight integers for faster calculation (and got the conversion wrong at one of the edge cases).