The following seems to be accurate 

$max_unsigned_int = ~0;
$max_signed_int   = -1 >> 1;

[download]

according to perlop:

Unary "~" performs bitwise negation, i.e., 1’s complement. For example, "0666 & ~027" is 0640. (See also "Integer Arithmetic" and "Bitwise String Operators".) Note that the width of the result is platform-dependent: ~0 is 32 bits wide on a 32-bit platform, but 64 bits wide on a 64-bit platform, so if you are expecting a certain bit width, remember to use the & operator to mask off the excess bits.

In reply to Re: portably finding max integer by shmem
in thread portably finding max integer by martin

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