Function initReadFrame

src/simplicity/frame.h:31–39

Initialize a new read frame. * 'n' is the number of cells for the read frame. * 'from' is a pointer to the beginning of the new slice for the array of UWORDS to hold the frame's cells. * * Precondition: UWORD from[ROUND_UWORD(n)]; */

 * Precondition: UWORD from[ROUND_UWORD(n)];
 */
static inline frameItem initReadFrame(size_t n, UWORD* from) {
  const size_t len = ROUND_UWORD(n);
/* '(1U * len) * UWORD_BIT - n' equals the number of padding bits in a frame of size 'n'.
 * Note that even if (len * UWORD_BIT) overflows,
 * (1) We have ensured an unsigned computation by multiplying by 1U so the behaviour is well-defined.
 * (2) after subtracting 'n' we are left with a value in the range 0 .. UWORD-BIT - 1.
 */
  return (frameItem){ .edge = from + len, .offset = (1U * len) * UWORD_BIT - n };
}

/* Initialize a new write frame.
 * 'n' is the number of cells for the write frame.