测试100M(1亿)个元素的初始化时间长度作为效率对比参考值。CPU: Intel i5@2.90GHZ
最后封装一个优化后的自定义双字节memset函数。
cpp
typedef unsigned char uint8_t;
typedef unsigned short uint16_t;
typedef unsigned int uint32_t;
typedef unsigned long long uint64_t;
#define MAX_SIZE (1024*1024*100) //100MiByte
uint8_t pBuff[MAX_SIZE] = { 0 };
uint64_t len = MAX_SIZE;
uint16_t value = 0x1234;
uint8_t ch_High = value >> 8;
uint8_t ch_Low = value&0xFF;
//测试1:传统for运行耗时47ms
for (uint64_t i = 0; i < len/2; i++)
{
pBuff[i] = ch_High;
pBuff[i+1] = ch_Low;
}
//测试2:指针for运行耗时31ms
uint8_t* pt = pBuff;
for (uint64_t i = 0; i < len/2; i ++ )
{
*(uint16_t*)pt = value;
pt += 2;
}
//通过以上测试可以看出用指针赋值比传统数组赋值快51%
//故有优化后的my_memset函数,用于初始化双字节函数。
void my_memset(uint8_t *buf,uint16_t value,uint64_t len)
{
for (uint64_t i = 0; i < len/2; i ++)
{
*(uint16_t*)buf = value;//关键:指针类型的转换
buf += 2;
}
}
//整体测试使用
void main()
{
uint8_t testData[10] = { 0 };
my_memset(testData, 0x1234, sizeof(testData));
for (size_t i = 0; i < sizeof(testData); i++)
{
printf("%02x ",testData[i]);
}
}
//最终输出:34 12 34 12 34 12 34 12 34 12