Self-modifying code: Difference between revisions

Revision as of 17:15, 9 July 2024

Latest revision as of 15:26, 16 March 2025

(One intermediate revision by one other user not shown)

Line 4:

{{Use list-defined references|date=December 2021}}

{{Use American English|date=January 2019}}

In [[computer science]], '''self-modifying code''' ('''SMC''' or '''SMoC''') is [[source code|code]] that alters its own [[instruction (computer science)|instruction]]s while it is [[execution (computing)|executing]] – usually to reduce the [[instruction path length]] and improve [[computer performance|performance]] or simply to reduce otherwise [[duplicate code|repetitively similar code]], thus simplifying [[software maintenance|maintenance]]. The term is usually only applied to code where the self-modification is intentional, not in situations where code accidentally modifies itself due to an error such as a [[buffer overflow]].

Line 24 ⟶ 25:

* '''overlay of existing instructions''' (or parts of instructions such as opcode, register, flags or addresses) or

* '''direct creation of whole instructions''' or sequences of instructions in memory

* '''creatingcreation or modification of [[source code]] statements''' followed by a 'mini compile' or a dynamic interpretation (see [[eval]] statement)

* '''creating an entire program dynamically''' and then executing it

Line 139 ⟶ 140:

===Specialization===

Suppose a set of statistics such as average, extrema, ___location of extrema, standard deviation, etc. are to be calculated for some large data set. In a general situation, there may be an option of associating weights with the data, so each x_i is associated with a w_i and rather than test for the presence of weights at every index value, there could be two versions of the calculation, one for use with weights and one not, with one test at the start. Now consider a further option, that each value may have associated with it a booleanBoolean to signify whether that value is to be skipped or not. This could be handled by producing four batches of code, one for each permutation and code bloat results. Alternatively, the weight and the skip arrays could be merged into a temporary array (with zero weights for values to be skipped), at the cost of processing and still there is bloat. However, with code modification, to the template for calculating the statistics could be added as appropriate the code for skipping unwanted values, and for applying weights. There would be no repeated testing of the options and the data array would be accessed once, as also would the weight and skip arrays, if involved.

===Use as camouflage===