基于位图的最高优先级算法，256级

 

抢占式RTOS中目前常用的最高优先级搜索算法，用一个BIT标记该优先级是否有任务等待运行：

1、最低BIT表明最高优先级，最高自然是最低的优先级；

2、该BIT标记为1表明该优先级有等待激活的线程；

3，用一个256字节的数组标记每8bit(一个字节的位宽)的所有可能情况（空间换时间），因为只需要第一个不为0的最低位，即只对应一种状态。

 

这个算法能优点网上一大把，我就不说了，自己做了一个实现，相对用循环查标记字节来说，用了二分查找，对所有情况来说时间复杂度都是一样的，为RTOS线程调度提供比较高的可预测性。

 

用到的数据结构：

typedef union tagSysThrBitMapType
{
    SysU8    U8[32];
    SysU16    U16[16];
    SysU32    U32[8];
    SysU64    U64[4];
} SysThrBitMapType;
typedef struct tagSysThrPriorityArrayType
{
    SysU32                TheadCount;
    SysThrBitMapType    BitMap;
    SysThrType*         ActiveThreadList[SYS_MAX_PRIORITY];
    SysThrType*         InactiveThreadList[SYS_MAX_PRIORITY-1];
} SysThrPriorityArrayType;

 

 

实现细节

SysU8 SysThrGetHighestActivePriority()
{
    SysU8 HighestActivePriority;

    if(SysThrPriorityArray.BitMap.U64[0])
    {
        if(SysThrPriorityArray.BitMap.U32[0])
        {
            if(SysThrPriorityArray.BitMap.U16[0])
            {
                if(SysThrPriorityArray.BitMap.U8[0]) HighestActivePriority=SysThrBytePriority[SysThrPriorityArray.BitMap.U8[0]];
                else HighestActivePriority=8+SysThrBytePriority[SysThrPriorityArray.BitMap.U8[1]];
            }
            else
            {
                if(SysThrPriorityArray.BitMap.U8[2]) HighestActivePriority=2*8+SysThrBytePriority[SysThrPriorityArray.BitMap.U8[2]];
                else HighestActivePriority=3*8+SysThrBytePriority[SysThrPriorityArray.BitMap.U8[3]];
            }
        }
        else
        {
            if(SysThrPriorityArray.BitMap.U16[2])
            {
                if(SysThrPriorityArray.BitMap.U8[4]) HighestActivePriority=4*8+SysThrBytePriority[SysThrPriorityArray.BitMap.U8[4]];
                else HighestActivePriority=5*8+SysThrBytePriority[SysThrPriorityArray.BitMap.U8[5]];
            }
            else
            {
                if(SysThrPriorityArray.BitMap.U8[6]) HighestActivePriority=6*8+SysThrBytePriority[SysThrPriorityArray.BitMap.U8[6]];
                else HighestActivePriority=7*8+SysThrBytePriority[SysThrPriorityArray.BitMap.U8[7]];
            }
        }
    }
    else if(SysThrPriorityArray.BitMap.U64[1])
    {
        if(SysThrPriorityArray.BitMap.U32[2])
        {
            if(SysThrPriorityArray.BitMap.U16[4])
            {
                if(SysThrPriorityArray.BitMap.U8[8]) HighestActivePriority=8*8+SysThrBytePriority[SysThrPriorityArray.BitMap.U8[8]];
                HighestActivePriority=9*8+SysThrBytePriority[SysThrPriorityArray.BitMap.U8[9]];
            }
            else
            {
                if(SysThrPriorityArray.BitMap.U8[10]) HighestActivePriority=10*8+SysThrBytePriority[SysThrPriorityArray.BitMap.U8[10]];
                else HighestActivePriority=11*8+SysThrBytePriority[SysThrPriorityArray.BitMap.U8[11]];
            }
        }
        else
        {
            if(SysThrPriorityArray.BitMap.U16[6])
            {
                if(SysThrPriorityArray.BitMap.U8[12]) HighestActivePriority=12*8+SysThrBytePriority[SysThrPriorityArray.BitMap.U8[12]];
                else HighestActivePriority=13*8+SysThrBytePriority[SysThrPriorityArray.BitMap.U8[13]];
            }
            else
            {
                if(SysThrPriorityArray.BitMap.U8[14]) HighestActivePriority=14*8+SysThrBytePriority[SysThrPriorityArray.BitMap.U8[14]];
                else HighestActivePriority=15*8+SysThrBytePriority[SysThrPriorityArray.BitMap.U8[15]];;
            }
        }
    }
    else if(SysThrPriorityArray.BitMap.U64[2])
    {
        if(SysThrPriorityArray.BitMap.U32[4])
        {
            if(SysThrPriorityArray.BitMap.U16[8])
            {
                if(SysThrPriorityArray.BitMap.U8[16]) HighestActivePriority=16*8+SysThrBytePriority[SysThrPriorityArray.BitMap.U8[16]];
                else HighestActivePriority=17*8+SysThrBytePriority[SysThrPriorityArray.BitMap.U8[17]];
            }
            else
            {
                if(SysThrPriorityArray.BitMap.U8[18]) HighestActivePriority=18*8+SysThrBytePriority[SysThrPriorityArray.BitMap.U8[18]];
                else HighestActivePriority=19*8+SysThrBytePriority[SysThrPriorityArray.BitMap.U8[19]];
            }
        }
        else
        {
            if(SysThrPriorityArray.BitMap.U16[10])
            {
                if(SysThrPriorityArray.BitMap.U8[20]) HighestActivePriority=20*8+SysThrBytePriority[SysThrPriorityArray.BitMap.U8[20]];
                else HighestActivePriority=21*8+SysThrBytePriority[SysThrPriorityArray.BitMap.U8[21]];
            }
            else
            {
                if(SysThrPriorityArray.BitMap.U8[22]) HighestActivePriority=22*8+SysThrBytePriority[SysThrPriorityArray.BitMap.U8[22]];
                else HighestActivePriority=23*8+SysThrBytePriority[SysThrPriorityArray.BitMap.U8[23]];
            }
        }
    }
    else if(SysThrPriorityArray.BitMap.U64[3])
    {
        if(SysThrPriorityArray.BitMap.U32[6])
        {
            if(SysThrPriorityArray.BitMap.U16[12])
            {
                if(SysThrPriorityArray.BitMap.U8[24]) HighestActivePriority=24*8+SysThrBytePriority[SysThrPriorityArray.BitMap.U8[24]];
                else HighestActivePriority=25*8+SysThrBytePriority[SysThrPriorityArray.BitMap.U8[23]];
            }
            else
            {
                if(SysThrPriorityArray.BitMap.U8[26]) HighestActivePriority=26*8+SysThrBytePriority[SysThrPriorityArray.BitMap.U8[26]];
                else HighestActivePriority=27*8+SysThrBytePriority[SysThrPriorityArray.BitMap.U8[27]];
            }
        }
        else
        {
            if(SysThrPriorityArray.BitMap.U16[14])
            {
                if(SysThrPriorityArray.BitMap.U8[28]) HighestActivePriority=28*8+SysThrBytePriority[SysThrPriorityArray.BitMap.U8[28]];
                else HighestActivePriority=29*8+SysThrBytePriority[SysThrPriorityArray.BitMap.U8[29]];
            }
            else
            {
                if(SysThrPriorityArray.BitMap.U8[30]) HighestActivePriority=30*8+SysThrBytePriority[SysThrPriorityArray.BitMap.U8[30]];
                else HighestActivePriority=31*8+SysThrBytePriority[SysThrPriorityArray.BitMap.U8[31]];
            }
        }
    }
    return HighestActivePriority;
}

 

 忘记添加数组了

const SysU8 SysThrBytePriority[] =
{
    0, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
    4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
    5, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
    4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
    6, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
    4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
    5, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
    4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
    7, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
    4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
    5, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
    4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
    6, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
    4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
    5, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
    4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0
};

 

转载于:https://www.cnblogs.com/xivisi/archive/2012/05/01/2477593.html