cpp-asm-comparison/main.cpp at main · slymachenko/cpp-asm-comparison · GitHub

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#include <stdio.h>
#include <windows.h>

#define MAX_ITER 1000000000

__forceinline unsigned GetVal()
{
	return rand() % 100 + 1;
}

/* original equation
a * i + b * (c + i) + d * (j + i)
i, j - loop dependent
a, b, c, d - constants
*/

/* opitimized equation
(a + b + d) * i + b * c + d * j
Allows b * c and (a + b + d) to be calculated out of loop
*/

unsigned calc_cpp(unsigned a, unsigned b, unsigned c, unsigned d)
{
	unsigned res = 0, i = 0, j = MAX_ITER;
	// Assuming, n > 0
	do
	{
		res += (a + b + d) * i + b * c + d * j;
		--j;
	} while (++i < MAX_ITER);
	return res;
}

// UNOPTIMIZED READABLE VERSION
//
// unsigned calc_asm(unsigned a, unsigned b, unsigned c, unsigned d)
//{
//	__asm
//	{
//		// ecx = b * c
//		mov		ebx, b
//		mov		eax, c
//		mul		ebx // ebx (b) * eax (c) (result: first 32bit in eax, last 32bit in edx)
//		mov		ecx, eax
//		// ebx = a + b
//		add		ebx, a
//		// edx = d * MAX_ITER
//		mov		edx, d
//		mov		eax, MAX_ITER
//		mul		edx // edx (d) * eax (MAX_ITER) (result: first 32bit in eax, last 32bit in edx)
//		mov		edx, eax
//		// edx (d * MAX_ITER) += ecx (b * c)
//		add		edx, ecx
//		// ecx = MAX_ITER
//		mov		ecx, MAX_ITER
//		// eax = 0
//		xor eax, eax
//
//		/*
//			eax = 0
//			ebx = a + b
//			ecx = MAX_ITER
//			edx = d * MAX_ITER + b * c
//		*/
//
//	CNT:
//		// eax += edx (d * j + b * c)
//		// edx += ebx (a + b)
//		add		eax, edx
//		add		edx, ebx
//		dec		ecx // same as -> sub ecx, 1
//		jnz		CNT
//	}
//	// return eax (4byte value)
// }

unsigned calc_asm(unsigned a, unsigned b, unsigned c, unsigned d)
{
	__asm
	{
		// ecx = b * c
		mov		ebx, b
		mov		eax, c
		mul		ebx // ebx (b) * eax (c) (result: first 32bit in eax, last 32bit in edx)
		mov		edx, d
		mov		ecx, eax
		// ebx = a + b
		add		ebx, a
		// edx = d * MAX_ITER
		mov		eax, MAX_ITER
		mul		edx // edx (d) * eax (MAX_ITER) (result: first 32bit in eax, last 32bit in edx)
		mov		edx, eax
		// edx (d * MAX_ITER) += ecx (b * c)
		add		edx, ecx
		// ecx = MAX_ITER
		mov		ecx, MAX_ITER
		// eax = 0
		xor eax, eax

		/*
			eax = 0
			ebx = a + b
			ecx = MAX_ITER
			edx = d * MAX_ITER + b * c
		*/

	CNT:
		// eax += edx (d * j + b * c)
		// edx += ebx (a + b)
		add		eax, edx
			add		edx, ebx
			dec		ecx // same as -> sub ecx, 1
			jnz		CNT
	}
	// return eax (4byte value)
}

int main()
{
	unsigned a = GetVal(), b = GetVal(), c = GetVal(), d = GetVal();

	printf("Constants: a=%u\tb=%u\tc=%u\td=%u\n\n", a, b, c, d);

	printf("LAB RESULTS for (a + b + d) * i + b * c + d * j:\n");
	DWORD time_st = GetTickCount();
	printf("Result = %u\n", calc_cpp(a, b, c, d));
	time_st = GetTickCount() - time_st;
	printf("Work time of %u iterations of cpp code = %u ms\n", MAX_ITER, time_st);

	time_st = GetTickCount();
	printf("\nResult = %u\n", calc_asm(a, b, c, d));
	time_st = GetTickCount() - time_st;
	printf("Work time of %u iterations of asm code = %u ms\n", MAX_ITER, time_st);

	return 0;
}