U32-to-U8 conversion

/*
 * U32TO8_BIG(c, v) stores the 32-bit-value v in big-endian convention
 * into the unsigned char array pointed to by c.
 */
#define U32TO8_BIG(c, v)    do { \
  u32 x = (v); \
  u8 *d = (c); \
  d[0] = T8(x >> 24); \
  d[1] = T8(x >> 16); \
  d[2] = T8(x >> 8); \
  d[3] = T8(x); \
 } while (0)

/*
 * U32TO8_LITTLE(c, v) stores the 32-bit-value v in little-endian convention
 * into the unsigned char array pointed to by c.
 */
#define U32TO8_LITTLE(c, v)    do { \
  u32 x = (v); \
  u8 *d = (c); \
  d[0] = T8(x); \
  d[1] = T8(x >> 8); \
  d[2] = T8(x >> 16); \
  d[3] = T8(x >> 24); \
 } while (0)