Function getByte

src/simplicity/bitstring.h:42–53

Return 8 bits from a bitstring staring from the nth bit. * * Precondition: NULL != s * n + 8 <= s->len; */

 *               n + 8 <= s->len;
 */
static inline uint_fast8_t getByte(const bitstring *s, size_t n) {
  simplicity_assert(8 <= s->len);
  simplicity_assert(n <= s->len - 8);
  size_t total_offset = s->offset + n;
  if (total_offset % CHAR_BIT <= CHAR_BIT - 8) {
    return (uint_fast8_t)(0xff & (s->arr[total_offset / CHAR_BIT] >> (CHAR_BIT - 8 - (total_offset % CHAR_BIT))));
  } else {
    /* CHAR_BIT < total_offset % CHAR_BIT + 8 */
    return (uint_fast8_t)(0xff & (((1U * s->arr[total_offset / CHAR_BIT]) << (total_offset % CHAR_BIT - (CHAR_BIT - 8)))
                                  | (s->arr[total_offset / CHAR_BIT + 1] >> (CHAR_BIT - (total_offset % CHAR_BIT - (CHAR_BIT - 8))))));
  }
}
#endif