Asked by Walter Roberson
on 12 Jul 2011

In releases before 2010a, literal numbers inside int64() and uint64() calls were understood by MATLAB as meaning to parse the numbers as class double and to call the int64() or uint64() method on the resulting double. For example,

>> uint64(18446744073709551600) ans = 18446744073709551615

Starting with release 2010a, the literal numbers are instead fully valued at parse time and given appropriate type.

I do not have R2010a or later available, so I would ask that people investigate the limits of that parsing in the new versions and report back.

For example:

- is uint64(18446744073709551600+0) the same as uint64(18446744073709551600) ?
- ditto uint64(18446744073709551600*1) ?
- ditto uint64(+18446744073709551600) ?
- ditto uint64(18446744073709551600.) ?
- ditto uint64(18446744073709551600.1) ?
- ditto uint64(18446744073709551600e0) ?
- how about int64(2^64-15) ?
- is uint64(18446744073709551600/2) equal to uint64(9223372036854775800) ?

And more generally, is there any expression X whose absolute value does not exceed 2^53, for which

B = int64(X);

is not the same as

A = X; B = uint64(A);

?

Answer by Friedrich
on 12 Jul 2011

Hi,

tested with R2011a 64bit on Win7:

>> int64(18446744073709551600)

ans =

9223372036854775807

>> uint64(18446744073709551600+0)

ans =

18446744073709551615

>> uint64(18446744073709551600*1)

ans =

18446744073709551615

>> uint64(+18446744073709551600)

ans =

18446744073709551615

>> uint64(18446744073709551600.)

ans =

18446744073709551615

>> uint64(18446744073709551600.1)

ans =

18446744073709551615

>> uint64(18446744073709551600e0)

ans =

18446744073709551615

>> int64(2^64-15)

ans =

9223372036854775807

>> uint64(18446744073709551600/2)

ans =

9223372036854775808

>> uint64(9223372036854775800)

ans =

9223372036854775800

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