Difference between revisions of "W1251 Parameter Passing"
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== Background == | |||
=== The Stack === | |||
An operating system provides an executing program with a structure called a '''stack'''. (Multithreaded programs may be provided with one stack per thread.) The stack is used by the application to ensure that when the invocation of a function completes, controls returns to the proper location, i.e., the next statement after the function invocation. A stack is a data structure that maintains its elements in a certain order, namely '''Last-In-First-Out'''. This means that the most recent element placed on the stack is the first one to be removed. Placing an element on the stack is performed by a '''PUSH''' operation, while removing an element from the stack (always the top-most element), is performed by a '''POP''' operation. The ''top'' of the stack is tracked in a special processor register called the '''stack pointer'''. | |||
=== PUSH Operation === | |||
The PUSH operation performs the following steps: | |||
# Write the data to the location immediately ''above'' the current stack pointer | |||
# Decrement the stack pointer so that it points at the next available location | |||
{| | |||
| style="vertical-align: top;" | Let's consider an example where we '''push''' three elements on to the stack: 57, 42, and 84. We begin with an empty stack. | |||
|[[File:Stack-Empty.png|thumb|right]] | |||
|- | |||
| style="vertical-align: top;" | We then PUSH(57). Remember that we write the data to the location immediately ''above'' the current stack pointer and then decrement the stack pointer. | |||
|[[File:Stack-57.png|thumb|right]] | |||
|- | |||
|We then PUSH(42). | |||
|- | |||
|And finally, we PUSH(84). | |||
|} | |||
== Research == | == Research == | ||
* Read [[Media:ComputerScienceOne.pdf| Section 5.2 (Computer Science I Textbook by Bourke)]] | * Read [[Media:ComputerScienceOne.pdf| Section 5.2 (Computer Science I Textbook by Bourke)]] | ||
Revision as of 21:41, 10 April 2019
Background[edit]
The Stack[edit]
An operating system provides an executing program with a structure called a stack. (Multithreaded programs may be provided with one stack per thread.) The stack is used by the application to ensure that when the invocation of a function completes, controls returns to the proper location, i.e., the next statement after the function invocation. A stack is a data structure that maintains its elements in a certain order, namely Last-In-First-Out. This means that the most recent element placed on the stack is the first one to be removed. Placing an element on the stack is performed by a PUSH operation, while removing an element from the stack (always the top-most element), is performed by a POP operation. The top of the stack is tracked in a special processor register called the stack pointer.
PUSH Operation[edit]
The PUSH operation performs the following steps:
- Write the data to the location immediately above the current stack pointer
- Decrement the stack pointer so that it points at the next available location
| Let's consider an example where we push three elements on to the stack: 57, 42, and 84. We begin with an empty stack. | |
| We then PUSH(57). Remember that we write the data to the location immediately above the current stack pointer and then decrement the stack pointer. | |
| We then PUSH(42). | |
| And finally, we PUSH(84). |
