Step by Step solution about How to resolve the algorithm Partial function application step by step in the C programming language

The provided C code demonstrates the use of the partial function, which creates a specialized function that applies a given function to each element of an array partially. Here's a detailed explanation of the code:

1. Header Includes: The code includes necessary header files:

   • <stdio.h> for input and output
   • <unistd.h> for fork, execvp, and other system calls
   • <stdlib.h> for exit and system
   • <dlfcn.h> for dynamic library loading and symbol lookup
   • <sys/wait.h> for waitpid
   • <err.h> for error handling

2. Function Declarations:

   • typedef int (*intfunc)(int);: Defines a function pointer type intfunc that points to functions taking an integer argument and returning an integer.
   • typedef void (*pfunc)(int*, int);: Defines a function pointer type pfunc that points to functions taking an integer array and its length as arguments.

3. partial Function:

   • The partial function takes an intfunc (a function pointer to a function that takes an integer and returns an integer) as input and returns a pfunc (a function pointer to a function that takes an integer array and its length).
   • It generates a dynamic library (/tmp/stuff<idx>.so) using the C preprocessor (#define, #xat, and #). The library defines a function _ that applies the provided intfunc to each element of an integer array.
   • Static variable idx keeps track of which dynamic library to name.
   • It loads the dynamic library, retrieves the symbol _ (the specialized function), and unlinks the library after use.

4. Sample Functions:

   • square: A sample function that squares its integer input.
   • dbl: A sample function that doubles its integer input.

5. main Function:

   • In main, two integer arrays x and y are initialized.
   • f is a pfunc that partially applies square to each element of an array.
   • g is a pfunc that partially applies dbl to each element of an array.
   • The code demonstrates the use of f and g by applying them to x and y and then printing the result.

This code showcases a technique for dynamically generating specialized functions that apply a given function to each element of an array in a partial fashion. This technique can be useful for optimizing or customizing computations.

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <dlfcn.h>
#include <sys/wait.h>
#include <err.h>

typedef int (*intfunc)(int);
typedef void (*pfunc)(int*, int);

pfunc partial(intfunc fin)
{
	pfunc f;
	static int idx = 0;
	char cc[256], lib[256];
	FILE *fp;
	sprintf(lib, "/tmp/stuff%d.so", ++idx);
	sprintf(cc, "cc -pipe -x c -shared -o %s -", lib);

	fp = popen(cc, "w");
	fprintf(fp, "#define t typedef\xat int _i,*i;t _i(*__)(_i);__ p =(__)%p;"
		"void _(i _1, _i l){while(--l>-1)l[_1]=p(l[_1]);}", fin);
	fclose(fp);

	*(void **)(&f) = dlsym(dlopen(lib, RTLD_LAZY), "_");
	unlink(lib);
	return f;
}

int square(int a)
{
	return a * a;
}

int dbl(int a)
{
	return a + a;
}

int main()
{
	int x[] = { 1, 2, 3, 4 };
	int y[] = { 1, 2, 3, 4 };
	int i;

	pfunc f = partial(square);
	pfunc g = partial(dbl);

	printf("partial square:\n");
	f(x, 4);
	for (i = 0; i < 4; i++) printf("%d\n", x[i]);

	printf("partial double:\n");
	g(y, 4);
	for (i = 0; i < 4; i++) printf("%d\n", y[i]);

	return 0;
}


partial square:
1
4
9
16
partial double:
2
4
6
8