c# - Mathematical operations on packed numerical values -

given following code packing 4 byte values uint.

private static void pack(byte x, byte y, byte z, byte w) {     this.packedvalue = (uint)x |                        ((uint)y << 8) |                        ((uint)z << 16) |                        ((uint)w << 24); } 

is possible apply mathematical operators *, +, / , - on value in manner can unpacked correct byte equivalent?

edit.

to clarify, if attempt multiply value packed value

uint result  = this.packedvalue * other.packedvalue  

then unpack using following...

public byte[] tobytes() {     return new[]     {         (byte)(this.packedvalue & 0xff),         (byte)((this.packedvalue >> 8) & 0xff),         (byte)((this.packedvalue >> 16) & 0xff),         (byte)((this.packedvalue >> 24) & 0xff)     }; } 

i wrong results.

here's full code sample showing expected , actual result.

void main() {     uint x = packuint(128, 128, 128, 128);     uint y = (uint)(x * 1.5f);      byte[] b1 = tobytes(x);     x.dump(); // 2155905152     b1.dump(); // 128, 255, 128, 255 right!     byte[] b2 = tobytes(y);     b2.dump(); // 0, 192, 192, 192 wrong! should 192, 192, 192, 192  }  // define other methods , classes here private static uint packuint(byte x, byte y, byte z, byte w) {     return ((uint)x) |            ((uint)y << 8) |            ((uint)z << 16) |            ((uint)w << 24); }  public static byte[] tobytes(uint packed) {     return new[]     {         (byte)(packed & 0xff),         (byte)((packed >> 8) & 0xff),         (byte)((packed >> 16) & 0xff),         (byte)((packed >> 24) & 0xff)     }; } 

the reason doesn't work 1.5f because floats not precise enough. try 1.5d (for double) , example work. approach limited "nice" cases, i.e. result in each byte guaranteed whole number. special case when multiply integer, work long none of 4 results overflow.

it possible addition , subtraction provided none of individual bytes overflow. overflow mess nearby bytes. particularly problematic if wish use 2's complement negative bytes (-128 .. 127) because adding 3 -2 "overflow" , mess next byte.