Overflow flag

Computer arithmetic

In computer processors, the overflow flag (sometimes called the V flag) is usually a single bit in a system status register used to indicate when an arithmetic overflow has occurred in an operation, indicating that the signed two's-complement result would not fit in the number of bits used for the result. Some architectures may be configured to automatically generate an exception on an operation resulting in overflow. An example, suppose we add 127 and 127 using 8-bit registers. 127+127 is 254, but using 8-bit arithmetic the result would be 1111 1110 binary, which is the two's complement encoding of −2, a negative number. A negative sum of positive operands (or vice versa) is an overflow. The overflow flag would then be set so the program can be aware of the problem and mitigate this or signal an error. The overflow flag is thus set when the most significant bit (here considered the sign bit) is changed by adding two numbers with the same sign (or subtracting two numbers with opposite signs). Overflow cannot occur when the sign of two addition operands are different (or the sign of two subtraction operands are the same). When binary values are interpreted as unsigned numbers, the overflow flag is meaningless and normally ignored. One of the advantages of two's complement arithmetic is that the addition and subtraction operations do not need to distinguish between signed and unsigned operands. For this reason, most computer instruction sets do not distinguish between signed and unsigned operands, generating both (signed) overflow and (unsigned) carry flags on every operation, and leaving it to following instructions to pay attention to whichever one is of interest. Internally, the overflow flag is usually generated by an exclusive or of the internal carry into and out of the sign bit. Bitwise operations (and, or, xor, not, rotate) do not have a notion of signed overflow, so the defined value varies on different processor architectures. Some processors clear the bit unconditionally (which is useful because bitwise operations set the sign flag, and the clear overflow flag then indicates that the sign flag is valid), others leave it unchanged, and some set it to an undefined value. Shifts and multiplies do permit a well-defined value, but it is not consistently implemented. For example, the x86 instruction set only defines the overflow flag for multiplies and 1-bit shifts; multi-bit shifts leave it undefined. (Wikipedia).

IDEspinner Buffer Overflows pt1

This movie tries to show how you can create a bufferoverflow Credits go out to IDEspinner

From playlist Buffer overflow

Buffer Overflow No ASLR

From playlist Buffer overflow

Tutorial: GeoHTTP Remote Buffer Overflow and DoS

A real example of a Buffer Overflow/Denial of Service attack! My favorite video: http://www.youtube.com/watch?v=z00kuZIVXlU Visit http://binslashshell.wordpress.com and join our forum community!!! This is a video showing what a Buffer Overflow Aattck can do to a Web Server. For th

From playlist Denial of Service attacks

Bufferoverflow part 3 - exploit coding for a commandline attack vector 1/2

Credits go out to IDEspinner, checkout his website: http://www.crackingislife.com/ clip 1/2

From playlist Buffer overflow

Hello LaTeX

In this video, we take a look at how you can quickly create the LaTeX logo on overleaf.

From playlist Tech Ideas

Bufferoverflow part 3 - exploit coding for a commandline attack vector 2/2

Credits go out to IDEspinner, checkout his website: http://www.crackingislife.com/ clip 2/2

From playlist Buffer overflow

Stack Overflow Inverted Index | MapReduce Use Case | MapReduce Design Patterns Tutorial | Edureka

Watch Sample Class recording: http://www.edureka.co/mapreduce-design-patterns?utm_source=youtube&utm_medium=referral&utm_campaign=stackover-mapreduce-design Stack overflow occurs if the stack pointer exceeds the stack bound. The call stack may consist of a limited amount of address space,

From playlist MapReduce Design Patterns Tutorial Videos

Bufferoverflow part 2- machine shellcoding 2/2

Credits go out to IDEspinner, checkout his website: http://www.crackingislife.com/ clip 2/2

From playlist Buffer overflow

Bufferoverflow part 2- machine shellcoding 1/2

Credits go out to IDEspinner, checkout his website: http://www.crackingislife.com/ clip 1/2

From playlist Buffer overflow

ELEC2141 Digital Circuit Design - Lecture 25

ELEC2141 Week 9 Lecture 3: Arithmetic Circuits

From playlist ELEC2141 Digital Circuit Design

NES Emulator Part #2: The CPU (6502 Implementation)

In this video I build a 6502 emulation in C++. I pay close attention to the instructions that can cause problems, ADC and SBC. Then I build a lightweight application to analyze running 6502 programs. Source: https://github.com/OneLoneCoder/olcNES YouTube: https://www.youtube.com/javidx9

From playlist NES Emulator From Scratch

28C3: Post Memory Corruption Memory Analysis (en)

For more information visit: http://bit.ly/28C3_information To download the video visit: http://bit.ly/28C3_videos Playlist 28C3: http://bit.ly/28C3_playlist Speaker: endrazine Automating exploitation of invalid memory writes Pmcma is a tool aimed at automating the most time cons

From playlist 28C3: Behind Enemy Lines

0037 (part 1) - Custom C++ Web Server: refactoring

This is #37 in my series of live (Twitch) coding streams, working on writing my own web server and service framework in C++. This stream I worked on more refactoring: * Removing std::shared_ptr where I don't really need it. * Use SHA-1 to calculate entity tags. * Clean up lifecycle method

From playlist Excalibur

Embedded Systems - Chap 5b - Timers - Professor E. Ambikairajah - UNSW Sydney

Electrical Systems Design (Embedded Systems Design) - Timers - Computer Interfacing - Microcontrollers - Electronic Whiteboard-Based Lecture - Lecture notes available from: http://eemedia.ee.unsw.edu.au/contents/elec2117/LectureNotes/

From playlist Introduction to Embedded Systems - by Professor Eliathamby Ambikairajah UNSW Sydney

How Computers Calculate - the ALU: Crash Course Computer Science #5

Today we're going to talk about a fundamental part of all modern computers. The thing that basically everything else uses - the Arithmetic and Logic Unit (or the ALU). The ALU may not have to most exciting name, but it is the mathematical brain of a computer and is responsible for all the

From playlist Computer Science

Section 9: More Comfortable

From playlist CS50 Sections 2012

RubyConf 2017: Buuuuugs iiiiin Spaaaaace! by Colin Fulton

RubyConf 2017: Buuuuugs iiiiin Spaaaaace! by Colin Fulton Space is really cool. From precision electronics, to giant rockets, spacecraft can represent the best of engineering. But sometimes things go wrong. Terribly wrong. What do exploding Soviet rockets have to do with Agile developmen

From playlist RubyConf 2017

DEFCON 15: (un)Smashing the Stack: Overflows, Countermeasures, and the Real World

Speaker: Shawn Moyer Chief Researcher, SpearTip Technologies As of today, Vista, XP, 2K03, OS X, every major Linux distro, and each of the BSD's either contain some facet of (stack|buffer|heap) protection, or have one available that's relatively trivial to implement/enable. So, this shoul

From playlist DEFCON 15

LESSON 30: Advanced Software Interrupt Techniques for Reading Serial Data on Arduino

You guys can help me out over at Patreon, and that will keep this high quality content coming: https://www.patreon.com/PaulMcWhorter This lesson shows how to use software interrupts to read serial data on the Arduino. This is demonstrated using the adafruit ultimate gps. You can follow t

From playlist Arduino Lessons

Underactive thyroid.mov

An general explanation of the underactive thyroid.

From playlist For Patients

Overflow flag

Related pages