Contains uint64 sybmol

contains.go

// Say you want to search 0x22 symbol in two bytes of 0x2122
// you make mask for your search as 0x2222
// then:
//
//   00100001 00100010
// ^ 00100010 00100010
// -------------------
//   00000011 00000000                     00000011 00000000
// & 01111111 11111111 (cut topmost bit) & 10000000 10000000 (save restore mask)
// -------------------                   -------------------
//   00000011 00000000                     00000000 00000000
// + 01111111 01111111
// -------------------
//   10000010 01111111
// | 00000000 00000000 (restore topmost bit)
// -------------------
//   10000010 01111111
// | 01111111 01111111
// -------------------
//   11111111 01111111
// ^ -----------------
//   00000000 10000000 != 0, then it contains string
//
// We do not make safe checks for bits overflow, cause ascii symbol is at most 0x7f.
func contains(a, b uint64) bool {
	const topmost = 0x7f7f7f7f7f7f7f7f
	const restore = &topmost
	v := a ^ b

	safe := v & topmost // cut top most bit preventing overflow
	rest := v & restore // save top most bit restore mask

	v = safe + topmost
	v &= rest // restore bits
	v |= topmost
	return ^v != 0
}