Decimal to Binary - Optimising

[wossname]

Following JMC's lead I thought it would be fun to do it in C#.

The code is longer but its actually about 5 times faster. No concatenation, no floating point operations. I have used uint's instead of int32's because there is no requirement for converting negative numbers and the largest number containable is twice as large.

I know its in C# but that's the idea, C# lets you use pointers and unmanaged arrays and stuf like that. I just benchmarked this and it runs 1,000,000 (1 million) times in an average time of 0.66 seconds on my old, slow P4 1.8ghz PC.

Whoooooosh! I can't get it to go any faster at the moment, if anyone knows a quicker way then let me know.

public static unsafe string ToBinary(uint val)
{
    sbyte* bin = stackalloc sbyte[32]; //32 bytes
    sbyte* index = bin; //duplicate the array pointer and use this as the iterator
    sbyte* stop = bin + 32; //stop after 32 bytes in the array

    uint mask = 0x80000000; //bit mask

    do
    {
        if((val & mask) != 0)
            *index =  (sbyte)0x31; 
        else
            *index =  (sbyte)0x30; 

        mask >>= 1;
    } while(++index != stop); //let the index catch up the buffer one and then stop

    index = bin; //reset pointer
    for(mask = 0; mask < 32 ; mask++)
        if(*(index++) == 0x31)
            break;

    return new string(bin, (int)mask, (int)(32 - mask));
} 

[yrwyddfa]

Yeah the first thing I noticed about Wossy's code is that he straight away went for stack allocations.

The standard VB6 code uses two heap allocations just to set up the array. You should probably use SafeArrayCreateVectorEx to reduce this to just one heap allocation (heap allocations are expensive)

There are some (advanced) techniques to get VB to allocate safe array memory on the stack but I won't go into them here (unless you really really want me to)