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In a stack machine, the operands used in the instructions are always at a known offset (set in the stack pointer), from a fixed location (the bottom of the stack, which in a hardware design might always be at memory location zero), saving precious in-cache or in-CPU storage from being used to store quite so many memory addresses or index ...
(In the examples that follow, a, b, and c are (direct or calculated) addresses referring to memory cells, while reg1 and so on refer to machine registers.) C = A+B 0-operand (zero-address machines), so called stack machines: All arithmetic operations take place using the top one or two positions on the stack: [9] push a, push b, add, pop c.
Enter stack frame: Modifies stack for entry to procedure for high level language. Takes two operands: the amount of storage to be allocated on the stack and the nesting level of the procedure. INSB/INSW: 6C Input from port to string. May be used with a REP prefix to repeat the instruction CX times. equivalent to:
A stack machine has most or all of its operands on an implicit stack. Special purpose instructions also often lack explicit operands; for example, CPUID in the x86 architecture writes values into four implicit destination registers.
The 8087 (The floating point math coprocessor) is a stack machine, though. Added x87 as an example of hybrids between stack and register machines. DBSand 05:30, 1 April 2011 (UTC)DBSand Most stack machines are, infact two-stack machines. One for operands and one for loop counters.
In an attempt to make Turing machine more intuitive, Z. A. Melzak consider the task of computing with positive numbers. The machine has an infinite abacus, an infinite number of counters (pebbles, tally sticks) initially at a special location S. The machine is able to do one operation:
The simple model provided in a stack-oriented language allows expressions and programs to be interpreted simply and theoretically evaluated much faster, since no syntax analysis needs to be done but lexical analysis. The way such programs are written facilitates being interpreted by machines, which is why PostScript suits printers well for its use.
This type of stack is also known as an execution stack, program stack, control stack, run-time stack, or machine stack, and is often shortened to simply the "stack". Although maintenance of the call stack is important for the proper functioning of most software , the details are normally hidden and automatic in high-level programming languages .