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The name "peek" is similar to the basic "push" and "pop" operations on a stack, but the name for this operation varies depending on data type and language. Peek is generally considered an inessential operation, compared with the more basic operations of adding and removing data, and as such is not included in the basic definition of these data ...
Similarly to a stack of plates, adding or removing is only practical at the top. Simple representation of a stack runtime with push and pop operations.. In computer science, a stack is an abstract data type that serves as a collection of elements with two main operations:
The stack is often used to store variables of fixed length local to the currently active functions. Programmers may further choose to explicitly use the stack to store local data of variable length. If a region of memory lies on the thread's stack, that memory is said to have been allocated on the stack, i.e. stack-based memory allocation (SBMA).
With a stack stored completely in RAM, this does implicit writes and reads of the in-memory stack: Load X, push to memory; Load 1, push to memory; Pop 2 values from memory, add, and push result to memory; for a total of 5 data cache references. The next step up from this is a stack machine or interpreter with a single top-of-stack register.
An abstract stack is a last-in-first-out structure, It is generally defined by three key operations: push, that inserts a data item onto the stack; pop, that removes a data item from it; and peek or top, that accesses a data item on top of the stack without removal.
The Sinclair QL has PEEK_W and POKE_W for 16-bit values and PEEK_L and POKE_L for 32-bit values. ST BASIC for the Atari ST uses the traditional names but allows defining 8/16/32 bit memory segments and addresses that determine the size. A Linux command line peekpoke [6] utility has been developed mainly for ARM based single board computers.
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Typically push and pop are translated into multiple micro-ops, to separately add/subtract the stack pointer, and perform the load/store in memory. [3] Newer processors contain a dedicated stack engine to optimize stack operations. Pentium M was the first x86 processor to introduce a stack engine.