Tuesday, 5 March 2013

Arithmetic overflow



The term arithmetic overflow or simply overflow has the following meanings. In a computer, the condition that occurs when a calculation produces a result that is greater in magnitude than that which a given register or storage location can store or represent. In a computer, the amount by which a calculated value is greater in magnitude than that which a given register or storage location can store or represent. Note that the overflow may be placed at another location.

Most computers distinguish between two kinds of overflow conditions. A carry occurs when the result of an addition or subtraction, considering the operands and result as unsigned numbers, does not fit in the result. Therefore, it is useful to check the carry flag after adding or subtracting numbers that are interpreted as unsigned values. An overflow proper occurs when the result does not have the sign that one would predict from the signs of the operands. Therefore, it is useful to check the overflow flag after adding or subtracting numbers that are represented in two's complement form.

Thursday, 12 July 2012

Traffic shaping

Traffic shaping (also known as "packet shaping") is a computer network traffic management technique which delays some or all datagrams to bring them into compliance with a desired traffic profile. Traffic shaping is a form of rate limiting.

Traffic shaping is used to optimize or guarantee performance, improve latency, and/or increase usable bandwidth for some kinds of packets by delaying other kinds of packets that meet certain criteria. If a link becomes saturated to the point where there is a significant level of contention (either upstream or downstream) latency can rise substantially. As a result, traffic shaping can be used to prevent this from occurring and keep latency in check. Traffic shaping provides a means to control the volume of traffic being sent into a network in a specified period (bandwidth throttling), or the maximum rate at which the traffic is sent (rate limiting), or more complex criteria such as GCRA. This control can be accomplished in many ways and for many reasons; however traffic shaping is always achieved by delaying packets.

Traffic shaping is commonly applied at the network edges to control traffic entering the network, but can also be applied by the traffic source (for example, computer or network card) or by an element in the network. Traffic policing is the distinct but related practice of packet dropping and packet marking. The technique of selecting or categorising traffic into different types or classes is traffic classification.

Tuesday, 20 September 2011

Overflow (software)

OVERFLOW - the OVERset grid FLOW solver - is a software package for simulating fluid flow around solid bodies using computational fluid dynamics (CFD). It is a compressible 3-D flow solver that solves the time-dependent, Reynolds-averaged, Navier-Stokes equations using multiple overset structured grids.