enum枚举类型赋值之switch语句与显示类型转换(Explicit Type Conversion)速度之比较

最新推荐文章于 2024-04-22 22:34:40 发布

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最新推荐文章于 2024-04-22 22:34:40 发布

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分类专栏： c++ 文章标签： c++ enum switch 显示类型转换速度比较

本文链接：https://blog.youkuaiyun.com/u010452749/article/details/12618879

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先开门见山，直接给结论：switch语句比显示类型转换要快，至于快多少，在500000（50W）次下200us

以下代码运行平台：windows7，x86(32位)，2G内存，双核，CPU频率：3GHz，IDE：VS2010

有个疑问是：我的电脑是3GHz，为什么用QueryPerformanceFrequency，得出的是：2922451，应该是2922451000才对吧？

大家有什么意见？

#include <iostream>
#include <windows.h>
using namespace std;

class HARQ
{
public:
	EHARQFeedback m_eFeedback;
};

class Entity
{
public:	
	HARQ m_HARQPro[1];
	unsigned char m_byFeebackProNum;

	LARGE_INTEGER listart;
	LARGE_INTEGER liend;
	LONGLONG freq;
	LONGLONG start;
	LONGLONG end;
	double elapse;

	Entity();
	bool testSwitchSpeed(unsigned char *t_pbyMsg);
	bool testExplicitTypeConversion(unsigned char *t_pbyMsg);
};



void test_eNBULHARQ();

int main()
{
	unsigned char abyMsg[2];
	abyMsg[1] = 0;
	Entity en;
	en.testSwitchSpeed(abyMsg);
	en.testExplicitTypeConversion(abyMsg);
	return 0;
	/* 
	 * frq = 2922451
	 * 10000
	 * 1st
	 * 0.0444832 ms testSwitchSpeed
	 * 0.0472206 ms testExplicitTypeConversion	 
	 * 2nd
	 * 0.044141 ms testSwitchSpeed
	 * 0.0472206 ms testExplicitTypeConversion
	 * 3rd
	 * 0.0557751 ms testSwitchSpeed
	 * 0.0585125 ms testExplicitTypeConversion
	 * ******************************************
	 * 50000
	 * 1st
	 * 0.282297 ms testSwitchSpeed
	 * 0.300091 ms testExplicitTypeConversion
	 * 2nd
	 * 0.261424 ms testSwitchSpeed
	 * 0.311382 ms testExplicitTypeConversion
	 * 3rd
	 * 0.266899 ms testSwitchSpeed
	 * 0.285377 ms testExplicitTypeConversion
	 * ******************************************
	 * 500000
	 * 1st
	 * 2.77165 ms testSwitchSpeed
	 * 2.93007 ms testExplicitTypeConversion
	 * 2nd
	 * 2.70732 ms testSwitchSpeed
	 * 2.91262 ms testExplicitTypeConversion
	 * 3rd
	 * 2.67857 ms testSwitchSpeed
	 * 2.86609 ms testExplicitTypeConversion
	 */
	/*******************************************
	 * conclusion: switch语句比显示类型转换要快 *
	 *******************************************/
}

Entity::Entity()
{
	m_byFeebackProNum = 0;
	listart;
	QueryPerformanceFrequency(&listart);
	freq = listart.QuadPart;
	start = 0;
	end = 0;
	elapse = 0.0;
}

bool Entity::testSwitchSpeed(unsigned char *t_pbyMsg)
{
	QueryPerformanceCounter(&listart);
	for (int i = 0; i != 500000; ++i)
	{

		switch (t_pbyMsg[1])
		{ 
		case 0:
			m_HARQPro[m_byFeebackProNum].m_eFeedback = ACK;
			break;
		case 1:
			m_HARQPro[m_byFeebackProNum].m_eFeedback = NACK;
			break;
		default:
			cout << "error In Ue ULEntityProcess: m_eFeedback != ACK And NACK" << endl;
			return false;
			break;
		}
	}
	QueryPerformanceCounter(&liend);
	start = listart.QuadPart;
	end = liend.QuadPart;
	elapse = (end - start) * 1000.0 / freq; // s
	cout << elapse << " ms testSwitchSpeed" << endl;
	return true;
}

bool Entity::testExplicitTypeConversion(unsigned char *t_pbyMsg)
{
// 	start = 0;
// 	end = 0;
	QueryPerformanceCounter(&listart);
	for (int i = 0; i != 500000; ++i)
	{
		if (t_pbyMsg[1] != 0 && t_pbyMsg[1] != 1)
		{
			cout << "error In Ue ULEntityProcess: m_eFeedback != ACK And NACK" << endl;
			return false;
		}
		m_HARQPro[m_byFeebackProNum].m_eFeedback = (EHARQFeedback)(t_pbyMsg[1]);
	}
	QueryPerformanceCounter(&liend);
	start = listart.QuadPart;
	end = liend.QuadPart;
	elapse = (end - start) * 1000.0 / freq; // s
	cout << elapse << " ms testExplicitTypeConversion" << endl;
	return true;
}