How to resolve the algorithm Create an object at a given address step by step in the D programming language

Published on 12 May 2024 09:40 PM
#D

How to resolve the algorithm Create an object at a given address step by step in the D programming language

Table of Contents

Problem Statement

In systems programing it is sometimes required to place language objects at specific memory locations, like I/O registers, hardware interrupt vectors etc.

Show how language objects can be allocated at a specific machine addresses. Since most OSes prohibit access to the physical memory if it is not mapped by the application, as an example, rather than a physical address, take the address of some existing object (using suitable address operations if necessary).

For example:

Let's start with the solution:

Step by Step solution about How to resolve the algorithm Create an object at a given address step by step in the D programming language

Source code in the d programming language

import std.stdio ;

void main() {
    int[] arr ;
    foreach(i; [0,1,2,3])
        arr ~= i*(1 << 24) + 0x417e7e7e ;

    struct X {
        char[16] msg ;
    }

    X* xPtr ;
    int* iPtr ;
    float* fPtr ;

    int adrSpace = cast(int) arr.ptr ;
    // get address of an existing object arr

    xPtr = cast(X*) adrSpace ;
    // xPtr now point to arr, as a struct X
    writefln("arr(as X)'s msg = '%s' (len %d) @ 0x%08x",
        xPtr.msg, xPtr.msg.length, xPtr) ;

    iPtr = cast(int*) (adrSpace + 1 * 4 /*bytes*/) ;
    fPtr = cast(float*) iPtr ;
    // pointers now point to arr[1]
    writefln("arr[1] = 0x%8x (%9.4f) @ 0x%08X", *iPtr, *fPtr, iPtr) ;
    iPtr = cast(int*) (adrSpace + 3 * 4 /*bytes*/) ;
    fPtr = cast(float*) iPtr ;
    // pointers now point to arr[3]
    writefln("arr[3] = 0x%8x (%9.4f) @ 0x%08X", *iPtr, *fPtr, iPtr) ;
    *fPtr = 0.5f ; // change value
    writefln("arr[3] = 0x%8x (%9.4f) @ 0x%08X", *iPtr, *fPtr, iPtr) ;
}

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