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2010a and later parsing of int64() and uint64() ?

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);

?

0 Comments

Walter Roberson

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1 Answer

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

5 Comments

Friedrich on 19 Aug 2011

Hi,

sorry but I don't get your second part with the unary plus and minus. Could you please explain to me what I have to do?

int64(-9223372036854775808)

ans =

-9223372036854775808

Walter Roberson on 19 Aug 2011

Thanks. Could I ask you to check int64(+9223372036854775800) ?

Daniel on 19 Aug 2011

R2011a 64bit on Linux
>> int64(+9223372036854775800)
ans =
9223372036854775807

Friedrich

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