ARM inline assembly random number 1 - 255

// ------------------------------------------------------------------------------
// THE BEER-WARE LICENSE (Revision 43):
// <aaronryool@gmail.com> wrote this file. As long as you retain this notice you
// can do whatever you want with this stuff. If we meet some day, and you think
// this stuff is worth it, you can buy me a beer in return
// ------------------------------------------------------------------------------

unsigned __rand(unsigned y)
{
// Implementation of George Marsaglia's xorshift PRNG
// gets a number between 1 and 255
asm(
    "cpy %0, %1\n\t"
    "eor %0, %0, %0, lsl #13\n\t"
    "eor %0, %0, %0, lsr #9\n\t"
    "eor %0, %0, %0, lsr #7\n\t"
    "ldr r1, =255\n\t"
    "ldr r2, =0x1010102\n\t"
    "umull r3, r2, %0, r2\n\t"
    "mul r1, r2\n\t"
    "sub %0, r1, %0\n\t"
    "and %0, %0, #0xff\n\t"
    "add %0, %0, #1\n\t"
    : "=r"(y) : "r"(y) : );
    return y;

}