PERLNUMBER

NAME SYNOPSIS DESCRIPTION Storing numbers Numeric operators and numeric conversions Flavors of Perl numeric operations AUTHOR SEE ALSO

perlnumber - semantics of numbers and numeric operations in Perl

$n = 1234; # decimal integer

$n = 0b1110011; # binary integer $n = 01234; # octal integer $n = 0x1234; # hexadecimal integer $n = 12.34e-56; # exponential notation $n =

This document describes how Perl internally handles numeric values.

Perl's operator overloading facility is completely ignored here. Operator overloading allows user-defined behaviors for numbers, such as operations over arbitrarily large integers, floating points numbers with arbitrary precision, operations over ``exotic'' numbers such as modular arithmetic or p-adic arithmetic, and so on. See overload for details.

Perl can internally represent numbers in 3 different ways:
as native integers, as native floating point numbers, and as
decimal strings. Decimal strings may have an exponential
notation part, as in .
*Native* here means ``a format supported by the C
compiler which was used to build perl''.

The term ``native* does not mean quite as much when we talk
about native integers, as it does when native floating point
numbers are involved. The only implication of the term
``native* on integers is that the limits for the maximal
and the minimal supported true integral quantities are close
to powers of 2. However, ``native* floats have a most
fundamental restriction: they may represent only those
numbers which have a relatively ``short* representation
when converted to a binary fraction. For example, 0.9 cannot
be represented by a native float, since the binary fraction

- for 0.9 is infinite
- binary0.1110011001100...

with the sequence 1100 repeating again and again. In addition to this limitation, the exponent of the binary number is also restricted when it is represented as a floating point number. On typical hardware, floating point values can store numbers with up to 53 binary digits, and with binary exponents between -1024 and 1024. In decimal representation this is close to 16 decimal digits and decimal exponents in the range of -304..304. The upshot of all this is that Perl cannot store a number like 12345678901234567 as a floating point number on such architectures without loss of information.

Similarly, decimal strings can represent only those numbers
which have a finite decimal expansion. Being strings, and
thus of arbitrary length, there is no practical limit for
the exponent or number of decimal digits for these numbers.
(But realize that what we are discussing the rules for just
the *storage* of these numbers. The fact that you can
store such ``large* numbers does not mean that the
*operations* over these numbers will use all of the
significant digits. See ``Numeric operators and numeric
conversions* for details.)

In fact numbers stored in the native integer format may be stored either in the signed native form, or in the unsigned native form. Thus the limits for Perl numbers stored as native integers would typically be -2**31..2**32-1, with appropriate modifications in the case of 64-bit integers. Again, this does not mean that Perl can do operations only over integers in this range: it is possible to store many more integers in floating point format.

Summing up, Perl numeric values can store only those numbers which have a finite decimal expansion or a ``short'' binary expansion.

As mentioned earlier, Perl can store a number in any one of three formats, but most operators typically understand only one of those formats. When a numeric value is passed as an argument to such an operator, it will be converted to the format understood by the operator.

- Six such conversions are possible
- native integer --

These conversions are governed by the following general rules:

If the source number can be represented in the target form, that representation is used.

If the source number is outside of the limits representable
in the target form, a representation of the closest limit is
used. (*Loss of information*)

If the source number is between two numbers representable in
the target form, a representation of one of these numbers is
used. (*Loss of information*)

In native floating point --
conversions the magnitude of the result is less than or
equal to the magnitude of the source. (*``Rounding to
zero*.'')

If the decimal string -- conversion cannot be done without loss of information, the result is compatible with the conversion sequence decimal_string -- . In particular, rounding is strongly biased to 0, though a number like

has a chance of

being rounded to 1.

**RESTRICTION** : The conversions marked
with (*) above involve steps performed by the C
compiler. In particular, bugs/features of the compiler used
may lead to breakage of some of the above
rules.

Perl operations which take a numeric argument treat that argument in one of four different ways: they may force it to one of the integer/floating/ string formats, or they may behave differently depending on the format of the operand. Forcing a numeric value to a particular format does not change the number stored in the value.

All the operators which need an argument in the integer format treat the argument as in modular arithmetic, e.g., mod 2**32 on a 32-bit architecture. sprintf

therefore provides the same result

as sprintf .

Arithmetic operators except, no integer

force the argument into the floating point format.

Arithmetic operators except, use integer

Bitwise operators, no integer

force the argument into the integer format if it is not a string.

Bitwise operators, use integer

force the argument into the integer format

Operators which expect an integer

force the argument into the integer format. This is applicable to the third and fourth arguments of sysread, for example.

Operators which expect a string

force the argument into the string format. For example, this is applicable to printf .

Though forcing an argument into a particular form does not change the stored number, Perl remembers the result of such conversions. In particular, though the first such conversion may be time-consuming, repeated operations will not need to redo the conversion.

Ilya Zakharevich ilya@math.ohio-state.edu

Editorial adjustments by Gurusamy Sarathy

overload

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