Fix the comment for loopup table hash func.

namespace chromap {

// Note that the max kmer size is 28 and it is saved in a unsigned 64-bit

// integer. So it can right shift by one bit is lossless and safe. The minimizer

// only occurs once when the lowest bit of the key value is set to 1.

// Note that the max kmer size is 28 and its hash value is always saved in the

// lowest 56 bits of an unsigned 64-bit integer. When an element is inserted

// into the hash table, its hash value is left shifted by 1 bit and the lowest

// bit of the key value is set to 1 when the minimizer only occurs once. So

// right shift by one bit is lossless and safe.

#define KHashFunctionForIndex(a) ((a) >> 1)

#define KHashEqForIndex(a, b) ((a) >> 1 == (b) >> 1)

KHASH_INIT(/*name=*/k64, /*khkey_t=*/uint64_t, /*khval_t=*/uint64_t,