(2^32) - ((2^32)-1) did not return 1
And the group of Cambridge mathamaticians that wrote the ROM turned out to be one man.
"ZX81 ROM Assembly Listing"
You have to type the following sequence of keys:
P [Shift]I 2 [Shift]H 3 2 [Shift]O -
[Shift]I [Shift]I 2 [Shift]H 3 2 [Shift]O
- 1 [Shift]O Enter
PRINT (2**32)-((2**32)-1)
Also try this (SQR is entered as: [Shift]Enter H):
PRINT SQR 0.25
I think what was interesting was it used a kind of bytecode to run maths routines (similar to the Apple II's SWEET16 code).
In [1]: 2.0**64 - (2.0**64-1.0)
Out[1]: 0.0
In [2]: 2.0**64 == (2.0**64 - 1.0)
Out[2]: TrueGiven a four byte mantissa, it should be 1 for anything under and equal to 2^32 and 0 for anything over 2^32. Instead it outputted some random number. A bug in checking the flags or some-such. Or maybe a bug in the float to string routine.
>(- (expt 2 64) (- (expt 2 64) 1))
1
(- (expt 2.0 64) (- (expt 2.0 64) 1)) yields 0.