cryptography arithmetic tricks

• get the next m*SIZE

  # define WARP_SZ 32
  size_t n = (nelems+WARP_SZ-1) & ((size_t)0-WARP_SZ)

  0-WARP_SIZE = 0xffffffffffffffe0
  eo = 0b11100000
  it will select multiples of WARP_SZ
  nelems+WARP_SZ-1 will counter for the removed numbers by 00000

n will be [32, 64, 96, …]

• make a value to be 1<<N

  uiint32_t a;
  while(a & (a-1)) // equal to 0 only when a is 1<<N
    a -= (a&(0-a)); // subtract the first 1 bit