Function CityHash32

Sources/nCine/Base/HashFunctions.cpp:202–271

	}

	std::uint32_t CityHash32(const char* s, std::size_t len)
	{
		if (len <= 24) {
			return len <= 12
				? (len <= 4 ? Hash32Len0to4(s, len) : Hash32Len5to12(s, len))
				: Hash32Len13to24(s, len);
		}

		// len > 24
		std::uint32_t h = static_cast<std::uint32_t>(len), g = c1 * h, f = g;

		std::uint32_t a0 = Rotate32(Fetch32(s + len - 4) * c1, 17) * c2;
		std::uint32_t a1 = Rotate32(Fetch32(s + len - 8) * c1, 17) * c2;
		std::uint32_t a2 = Rotate32(Fetch32(s + len - 16) * c1, 17) * c2;
		std::uint32_t a3 = Rotate32(Fetch32(s + len - 12) * c1, 17) * c2;
		std::uint32_t a4 = Rotate32(Fetch32(s + len - 20) * c1, 17) * c2;
		h ^= a0;
		h = Rotate32(h, 19);
		h = h * 5 + 0xe6546b64;
		h ^= a2;
		h = Rotate32(h, 19);
		h = h * 5 + 0xe6546b64;
		g ^= a1;
		g = Rotate32(g, 19);
		g = g * 5 + 0xe6546b64;
		g ^= a3;
		g = Rotate32(g, 19);
		g = g * 5 + 0xe6546b64;
		f += a4;
		f = Rotate32(f, 19);
		f = f * 5 + 0xe6546b64;
		std::size_t iters = (len - 1) / 20;
		do {
			std::uint32_t b0 = Rotate32(Fetch32(s) * c1, 17) * c2;
			std::uint32_t b1 = Fetch32(s + 4);
			std::uint32_t b2 = Rotate32(Fetch32(s + 8) * c1, 17) * c2;
			std::uint32_t b3 = Rotate32(Fetch32(s + 12) * c1, 17) * c2;
			std::uint32_t b4 = Fetch32(s + 16);
			h ^= b0;
			h = Rotate32(h, 18);
			h = h * 5 + 0xe6546b64;
			f += b1;
			f = Rotate32(f, 19);
			f = f * c1;
			g += b2;
			g = Rotate32(g, 18);
			g = g * 5 + 0xe6546b64;
			h ^= b3 + b1;
			h = Rotate32(h, 19);
			h = h * 5 + 0xe6546b64;
			g ^= b4;
			g = ByteSwap32(g) * 5;
			h += b4 * 5;
			h = ByteSwap32(h);
			f += b0;
			PERMUTE3(f, h, g);
			s += 20;
		} while (--iters != 0);