Strange integer behaviour

[my216]

It's been 40 years since I last wrote any code for the ZX81 and I've forgotten any idiosyncrasies it may have had.

If I assign a number to a variable that is greater than 8 digits and then retrieve it with Print it is returned rounded.For example:

LET A = 123456789

PRINT A

1234567900

Also, if I convert A to a string it becomes "1234567900".

Can anyone remind me what is happening here? Thanks.

[stroebeljc]

The ZX81 is only capable of precision to 8 digits. Thus, the rounding.

[Moggy]

Internally accurate to 9 - 10 digits with 8 displayed after rounding.

[stroebeljc]

Internally accurate down to 1/(2^32) ~= 0.0000000002328306437. So, yes, 9 to 10 digits. 32/log2(10)=9.63, to be more precise.

[my216]

But it's not just printing. As converting the stored value to a string will also give the rounded to 8 digits number.

[stroebeljc]

Sort of like the calculators of the day.

[zx81jens]

Hello Users.

This is shown on Page 28:

https://www.historybit.it/wp-content/up ... amming.pdf

Greetings
Jens

[my216]

yep, but what it doesn't say is that although all digits of 4294967295 are apparently stored, if you do STR$ A (assuming the number is in A) you do not get "4294967295" but "4294967300"

[1024MAK]

The internal ROM function that converts a floating point number to a string is almost certainly the same routine that converts it for printing to the screen.

Mark

[Paul]

The internal ROM function that converts a floating point number to a string is almost certainly the same routine that converts it for printing to the screen.

Mark

You can delete the "almost"