Bounds checking

Abstract

A data processing apparatus is provided, for performing a determination of whether a value falls within a boundary defined by a lower limit between 0 and 2 m and an upper limit between 0 and 2 m. Theapparatus includes storage circuitry that stores each of the lower limit and the upper limit in a compressed form as a mantissa of q < m bits and a shared exponent e. A most significant m-q-e bits ofsaid lower limit and said upper limit are equal to a most significant m-q-e bits of said value. Adjustment circuitry performs adjustments to the lower limit and the upper limit in compressed form andboundary comparison circuitry performs the determination on the value using the lower limit and the upper limit in the compressed form.

Description

technical field [0001] This disclosure relates to bounds checking. By way of example only, the present disclosure may relate to memory bounds checking. Background technique [0002] It is often desirable to determine whether a value lies within boundaries defined by a lower bound and an upper bound. For example, in a memory system, memory may be partitioned into regions, where different processes "own" particular regions of memory. For security reasons, it is often desirable to prevent non-owning processes from accessing memory regions owned by another process. For this reason, attempts to access memory should be bounds checked in order to check whether the access is within the memory access area belonging to the currently executing process. As the memory system becomes larger, the size of the memory address also increases. So this not only increases the number of bits required to represent the memory location to be accessed, but also increases the number of bits require...

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Problems solved by technology

This in turn increases circuit size and thus power consumption

Also, comparing such a large number of bits becomes time-consuming

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