Merge pull request #19 from 4ms/smallest_integer

Determining smallest integer type that can represent a given value

Author: danngreen

util/smallest_integer.hh

@@ -0,0 +1,39 @@
+#pragma once
+
+#include <cstdint>
+#include <limits>
+#include <type_traits>
+
+template<uint64_t max_val>
+struct SmallestUnsignedInt {
+	using type = std::conditional_t<
+		max_val <= std::numeric_limits<uint8_t>::max(),
+		uint8_t,
+		std::conditional_t<max_val <= std::numeric_limits<uint16_t>::max(),
+						   uint16_t,
+						   std::conditional_t<max_val <= std::numeric_limits<uint32_t>::max(), uint32_t, uint64_t>>>;
+};
+
+template<int64_t min_val, int64_t max_val>
+requires(min_val <= max_val)
+struct SmallestSignedInt {
+	using type =
+		std::make_signed_t<typename SmallestUnsignedInt<(max_val >= -min_val ? max_val : -min_val - 1) << 1>::type>;
+};
+
+static_assert(std::is_same_v<SmallestUnsignedInt<0>::type, uint8_t>);
+static_assert(std::is_same_v<SmallestUnsignedInt<255>::type, uint8_t>);
+static_assert(std::is_same_v<SmallestUnsignedInt<256>::type, uint16_t>);
+static_assert(std::is_same_v<SmallestUnsignedInt<65535>::type, uint16_t>);
+static_assert(std::is_same_v<SmallestUnsignedInt<65536>::type, uint32_t>);
+static_assert(std::is_same_v<SmallestUnsignedInt<(1ull << 32) - 1>::type, uint32_t>);
+static_assert(std::is_same_v<SmallestUnsignedInt<1ull << 32>::type, uint64_t>);
+
+static_assert(std::is_same_v<SmallestSignedInt<0, 127>::type, int8_t>);
+static_assert(std::is_same_v<SmallestSignedInt<-128, 127>::type, int8_t>);
+static_assert(std::is_same_v<SmallestSignedInt<0, 128>::type, int16_t>);
+static_assert(std::is_same_v<SmallestSignedInt<-129, 0>::type, int16_t>);
+static_assert(std::is_same_v<SmallestSignedInt<0, 32767>::type, int16_t>);
+static_assert(std::is_same_v<SmallestSignedInt<-32768, 32767>::type, int16_t>);
+static_assert(std::is_same_v<SmallestSignedInt<-32768, 32768>::type, int32_t>);
+static_assert(std::is_same_v<SmallestSignedInt<-3293768, 3932768>::type, int32_t>);