Overflow of Integer and Float Values

This section describes what an arithmetic overflow condition, how the PHP 5 engine handles integer and float value overflow, how to write a PHP code to detect overflow conditions.

What is overflow? Overflow or arithmetic overflow is a condition that occurs when a calculation produces a result that is greater in magnitude than what a given data type can store or represent.

When applying this definition to PHP integer data type, we can say that: PHP integer value overflow is a condition when an integer operation produces an integer outside the signed 32-bit integer value range.

When applying this definition to PHP float data type, we can say that: PHP float value overflow is a condition when a float operation produces a float value outside the 64-bit floating point number value range.

According to the PHP manual, here is how the PHP 5 engine handles arithmetic overflow conditions:

Note that in all arithmetic overflow cases, PHP will not abend the operation and raise any runtime errors. So if you are writing a PHP code dealing with numbers that close to integer or float value range limits, you need to be very careful and write extra code to detect overflow conditions yourself.

To help us understand what are integer and float value range and how to detect arithmetic overflow conditions, I wrote this tutorial sample PHP script:

<?php /* NumericOverflow.php
 - Copyright (c) 2015, HerongYang.com, All Rights Reserved.
*/
print "\n Signed 32-bit integer positive overflow test:\n";
$integerLimit =  0x7FFFFFFF; 
$integerOverflow = $integerLimit + 1;
print "    Integer upper limit: "; var_dump($integerLimit);
print "   Upper limit overflow: "; var_dump($integerOverflow);

print "\n Signed 32-bit integer positive overflow test:\n";
$integerLimit =  -0x7FFFFFFF - 1;
$integerOverflow = $integerLimit - 1;
print "    Integer lower limit: "; var_dump($integerLimit);
print "   Lower limit overflow: "; var_dump($integerOverflow);

print "\n 64-bit floating point number overflow test:\n";
$floatLimit = 1.0;
$floatOverflow = $floatLimit*10;
while (!is_infinite($floatOverflow)) {
   $floatLimit *= 10;
   $floatOverflow = $floatLimit*10;
}	
print "   Float high limit: "; var_dump($floatLimit);
print "     Float overflow: "; var_dump($floatOverflow);

print "\n 64-bit floating point number underflow test:\n";
$floatLimit = 1.0;
$floatUnderflow = $floatLimit/10;
while (!$floatUnderflow==0) {
   $floatLimit /= 10;
   $floatUnderflow = $floatLimit/10;
}
print "   Float low limit: "; var_dump($floatLimit);
print "   Float underflow: "; var_dump($floatUnderflow);
?>

If you run this sample script, you should get:

 Signed 32-bit integer positive overflow test:
    Integer upper limit: int(2147483647)
   Upper limit overflow: float(2147483648)

 Signed 32-bit integer positive overflow test:
    Integer lower limit: int(-2147483648)
   Lower limit overflow: float(-2147483649)

 64-bit floating point number overflow test:
   Float high limit: float(1.0E+308)
     Float overflow: float(INF)

 64-bit floating point number underflow test:
   Float low limit: float(9.88131291682E-324)
   Float underflow: float(0)

The result tells me that on my computer:

Exercise: Modify my sample script to find out the negative float value range.

Last update: 2015.

Table of Contents

 About This Book

 Introduction and Installation of PHP 7.0

 PHP Script File Syntax

PHP Data Types and Data Literals

 Data Types Supported in PHP

 Data Literals Supported in PHP

 Data Literals Examples for Integer, String and Other Data Types

Overflow of Integer and Float Values

 Variables, References, and Constants

 Expressions, Operations and Type Conversions

 Conditional Statements - "if" and "switch"

 Loop Statements - "while", "for", and "do ... while"

 Function Declaration, Arguments, and Return Values

 Arrays - Ordered Maps

 Configuring and Sending out Emails

 Retrieving Information from HTTP Requests

 Creating and Managing Sessions in PHP Scripts

 Sending and Receiving Cookies in PHP Scripts

 Controlling HTTP Response Header Lines in PHP Scripts

 MySQL Server Connection and Access Functions

 Functions to Manage Directories, Files and Images

 SOAP Extension Function and Calling Web Services

 SOAP Server Functions and Examples

 Localization Overview of Web Applications

 Using Non-ASCII Characters in HTML Documents

 Using Non-ASCII Characters as PHP Script String Literals

 Receiving Non-ASCII Characters from Input Forms

 "mbstring" Extension and Non-ASCII Encoding Management

 Managing Non-ASCII Character Strings with MySQL Servers

 Introduction of Class and Object

 Integrating PHP with Apache Web Server

 Outdated Tutorials

 References

 PDF Printing Version