/* This is the value of the prime as four 64-bit words, little-endian. */
static const u64 kPrime[4] = { 0xfffffffffffffffful, 0xffffffff, 0, 0xffffffff00000001ul };
-static const limb bottom32bits = 0xffffffff;
static const u64 bottom63bits = 0x7ffffffffffffffful;
/* bin32_to_felem takes a little-endian byte array and converts it into felem