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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.
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.
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:
If the offset is zero, this becomes an example of register indirect addressing; the effective address is just the value in the base register. On many RISC machines, register 0 is fixed at the value zero. If register 0 is used as the base register, this becomes an example of absolute addressing.
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.
Whether you’ve got a can of bacon grease at the ready or you’re Team Butter, we won’t be swearing off the fats when we’re cooking around here.
PostScript is an example of a postfix stack-based language. An expression example in this language is 2 3 mul ('mul' being the command for the multiplication operation). Calculating the expression involves understanding how stack orientation works. Stack orientation can be presented as the following conveyor belt analogy.