ARM immediate value encoding

// Android Immediate Number Representation.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <iostream>

inline unsigned long RotateLeft(unsigned long n, unsigned long i)
{
  return (n << i) | (n >> (32 - i));
}

inline unsigned int RotateRight32Bit(unsigned int Data, unsigned int Bits) {
    return (Data >> Bits) | (Data << (32-Bits));
}

inline bool IsBlockSet(__int32 num, __int32 blockNum)
{
    blockNum *= 2;

    return ((1 << blockNum | 1 << (blockNum + 1)) & num) != 0;
}

int FindBlockOfFirstBit(__int32 num)
{
    for(int i = 0; i < 16; i++)
    {
        if(IsBlockSet(num, i))
            return i;
    }

    return 0;
}

inline int GetRemainder(int a, int b)
{
    return ((a % b) + b) % b;
}

inline unsigned int blockModulo(int blockNum)
{
    return GetRemainder(blockNum, 16);
}

int FindBlockOfLastBit(__int32 num)
{
    for(int i = 30; i >= 0; i -= 2)
    {
        if((1 << i | 1 << (i + 1)) & num)
            return i / 2;
    }

    return 0;
}

int GoForwardAndGetActiveBlock(__int32 num, int startBlock)
{
    for(int i = 3; i >= 1; i--)
    {
        int blockNum = startBlock + i;

        if(IsBlockSet(num, blockNum))
            return blockNum;
    }

    return startBlock;
}

int GoBackwardAndGetActiveBlock(__int32 num, int startBlock)
{
    for(int i = 3; i >= 1; i--)
    {
        int blockNum = startBlock - i;

        if(IsBlockSet(num, blockNum))
            return blockNum;
    }

    return startBlock;
}

bool GetARMImmediateNumberComponents(__int32 num, unsigned char* outNum, unsigned char* outRot)
{
    int start = FindBlockOfFirstBit(num);

    int forward = blockModulo(GoForwardAndGetActiveBlock(num, start));

    int backward = blockModulo(GoBackwardAndGetActiveBlock(num, forward));

    int end = blockModulo(backward + 4);

    forward *= 2;

    backward *= 2;

    end *= 2;

    __int32 mask;

    if(end < backward)
        mask = ~(((1 << (backward-end)) - 1) << end);
    else
        mask = ((1 << (end-backward)) - 1) << backward;

    __int32 leftOver = num  & ~mask;

    if(!leftOver)
    {
        *outRot = backward == 0 ? 0 : 32 - backward;

        *outNum = (char)RotateLeft(num & mask, *outRot);
        return true;
    }
    else
    {
        *outRot = -1;
        *outNum = -1;
        return false;
    }
}

inline unsigned short int GetARMImmediateNumberRepresentation(unsigned char outNum, unsigned char outRot)
{
    return outNum | ((outRot/2) << 8);
}

int main(int argc, char* argv[])
{
    unsigned char outNum;
    unsigned char outRot;

    // Please change a number here!
    bool bCanBeRepresentedAsImmediate = GetARMImmediateNumberComponents(0x0003FC00, &outNum, &outRot);

    if(bCanBeRepresentedAsImmediate)
    {
        unsigned short int result = GetARMImmediateNumberRepresentation(outNum, outRot);

        printf("Equation: 0x%X ROR %d Value: %02X", outNum, outRot, result);
    }
    else
        printf("This value can't be represented as ARM immediate.\n");

    getchar();

    return 0;
}