constant_time_select_int
static inline int constant_time_select_int(unsigned int mask, int a, int b);
one_index = constant_time_select_int(~found_one_byte & equals1,
tlen = constant_time_select_int(constant_time_lt(dblen - mdlen - 1, tlen),
msg_index = constant_time_select_int(good, msg_index, dblen - tlen);
return constant_time_select_int(good, mlen, -1);