How to "optimize" self-defined 32bit shift-left routine ?

Thanks for all your comments. After utilizing what you mentioned I got good result. Below is my routine for executing 32-bit shift left operation:

code UINT16 AndMask16bit[8]=
{
 0x0000,
 0x0001,0x0003,0x0007,0x000f,
 0x001f,0x003f,0x007f,
};

UINT32 ShiftLeft32Bits(UINT32 Operand, UINT8 ShiftValue)
{
        UINT8 remain;
        OperandDW = Operand;

        if(ShiftValue>=16)
        {
        remain = ShiftValue - 16;

        // shift left 16-bit first
        OperandDWHi = OperandDWLo;
        OperandDWLo = 0;

        // shift left with remaining bit number (<16)
        OperandDWHi = OperandDWHi << remain;
        }
        else if(ShiftValue>=8)
        {
        remain = ShiftValue - 8;
        // shift left 8 bit first
        OperandDWHiB3 = OperandDWHiB2;
        OperandDWHiB2 = OperandDWHiB1;
        OperandDWHiB1 = OperandDWHiB0;
        OperandDWHiB0 = 0;

        // shift left with remaining bit number (<8)

        // 1. shift high 16-bit first
        OperandDWHi = OperandDWHi << remain;

        // 2. rotate left low-16 bit
        OperandDWLo = _irol_(OperandDWLo,remain);

        // 3. get the part belonging to high 16bit
        OperandDWHi |= (OperandDWLo & (AndMask16bit[remain]));

        // 4. get the part belonging to low-16 bit
        OperandDWLo = OperandDWLo & ~(AndMask16bit[remain]);

        // end...

        }
        else if(ShiftValue>0)
        {
        // shift left high 16bit first
        OperandDWHi = OperandDWHi << ShiftValue;

        // shift left low 16bit
        OperandDWLo = _irol_(OperandDWLo,ShiftValue);

        // get the part belonging to high 16bit
        OperandDWHi |= (OperandDWLo & (AndMask16bit[ShiftValue]));

        // get the part belonging to low-16 bit
        OperandDWLo = OperandDWLo & ~(AndMask16bit[ShiftValue]);
        }

        return  OperandDW;
}

F.Y.I

Thanks for all your comments. After utilizing what you mentioned I got good result. Below is my routine for executing 32-bit shift left operation:

code UINT16 AndMask16bit[8]=
{
 0x0000,
 0x0001,0x0003,0x0007,0x000f,
 0x001f,0x003f,0x007f,
};

UINT32 ShiftLeft32Bits(UINT32 Operand, UINT8 ShiftValue)
{
        UINT8 remain;
        OperandDW = Operand;

        if(ShiftValue>=16)
        {
        remain = ShiftValue - 16;

        // shift left 16-bit first
        OperandDWHi = OperandDWLo;
        OperandDWLo = 0;

        // shift left with remaining bit number (<16)
        OperandDWHi = OperandDWHi << remain;
        }
        else if(ShiftValue>=8)
        {
        remain = ShiftValue - 8;
        // shift left 8 bit first
        OperandDWHiB3 = OperandDWHiB2;
        OperandDWHiB2 = OperandDWHiB1;
        OperandDWHiB1 = OperandDWHiB0;
        OperandDWHiB0 = 0;

        // shift left with remaining bit number (<8)

        // 1. shift high 16-bit first
        OperandDWHi = OperandDWHi << remain;

        // 2. rotate left low-16 bit
        OperandDWLo = _irol_(OperandDWLo,remain);

        // 3. get the part belonging to high 16bit
        OperandDWHi |= (OperandDWLo & (AndMask16bit[remain]));

        // 4. get the part belonging to low-16 bit
        OperandDWLo = OperandDWLo & ~(AndMask16bit[remain]);

        // end...

        }
        else if(ShiftValue>0)
        {
        // shift left high 16bit first
        OperandDWHi = OperandDWHi << ShiftValue;

        // shift left low 16bit
        OperandDWLo = _irol_(OperandDWLo,ShiftValue);

        // get the part belonging to high 16bit
        OperandDWHi |= (OperandDWLo & (AndMask16bit[ShiftValue]));

        // get the part belonging to low-16 bit
        OperandDWLo = OperandDWLo & ~(AndMask16bit[ShiftValue]);
        }

        return  OperandDW;
}

F.Y.I

I must be missing something of the plot here.

That looks like one of the ugliest shift left routines I think I've ever seen.

I must be missing something of the plot here.

This would be 'Bad decision at early design stage, have to pay a high price now.'
Why are early design decisions important? See here:
www.astrodigital.org/.../stshorse.html

I found one strange thing after investigation:

#1 In my current project 32bit shift right is ok.When I wrote:

x = (( ByteNumLo >> 31 ) & 0x01 ) + (( z >> 31 ) & 0x01 );

I found above example cost about 22us...

#2 If using self-defined routine like previous post:

x = (ShiftRight32Bits(ByteNumLo)&0x01)+(ShiftRight32Bits(z)&0x01);

I found it cost 9us...

Thus I think in some special cases self-defined routine is better than that in ?C?LIB_CODE even we consider it in early design...

F.Y.I

And just think what it could do it in if you had written in assembler!

Hmmmm.... that does very much rely on the skill of the particular assembly programmer...

Thus I think in some special cases self-defined routine is better than that in ?C?LIB_CODE even we consider it in early design...<p>

That's probably due to doing byte-wise shifts first.

This, of course, results in slightly larger code _and_ slightly more cycles in certain cases, but if the shift_value is evenly distributed, the optimization lowers the average cycle count.