Merge pull request #237 from elbeno/fix-smallest-uint-docs

🐛 Fix the docs for `smallest_uint`

Author: bdeane-intel

docs/bit.adoc

@@ -121,17 +121,20 @@ static_assert(stdx::bit_pack<std::uint32_t>(a[0], a[1]) == 0x1234'5678u);
 === `smallest_uint`
 
 `smallest_uint` is a function template that selects the smallest unsigned
-integral type that will fit a compile-time value.
+integral type that will fit a number of bits.
 
 [source,cpp]
 ----
-constexpr auto x = stdx::smallest_uint<42>();   // std::uint8_t{42}
-constexpr auto y = stdx::smallest_uint<1337>(); // std::uint16_t{1337}
+constexpr auto x = stdx::smallest_uint<4>();   // std::uint8_t{}
+constexpr auto y = stdx::smallest_uint<9>(); // std::uint16_t{}
 
 // smallest_uint_t is the type of a call to smallest_uint
-using T = stdx::smallest_uint_t<1337>; // std::uint16_t
+using T = stdx::smallest_uint_t<9>; // std::uint16_t
 ----
 
+NOTE: Giving `smallest_uint_t` any bit size over 64 will still return a
+`std::uint64_t`.
+
 === `to_be`, `from_be`, `to_le`, `from_le`
 
 `to_be` and `from_be` are variations on `byteswap` that do the job of

include/stdx/bit.hpp

@@ -421,13 +421,13 @@ template <typename T> constexpr auto bit_size() -> std::size_t {
 
 template <std::size_t N> CONSTEVAL auto smallest_uint() {
     if constexpr (N <= std::numeric_limits<std::uint8_t>::digits) {
-        return std::uint8_t{N};
+        return std::uint8_t{};
     } else if constexpr (N <= std::numeric_limits<std::uint16_t>::digits) {
-        return std::uint16_t{N};
+        return std::uint16_t{};
     } else if constexpr (N <= std::numeric_limits<std::uint32_t>::digits) {
-        return std::uint32_t{N};
+        return std::uint32_t{};
     } else {
-        return std::uint64_t{N};
+        return std::uint64_t{};
     }
 }
 

test/bit.cpp

@@ -421,3 +421,14 @@ TEST_CASE("bit_pack/unpack round trip 64 <-> 32", "[bit]") {
     auto const [a, b] = stdx::bit_unpack<std::uint32_t>(x);
     CHECK(stdx::bit_pack<std::uint64_t>(a, b) == x);
 }
+
+TEST_CASE("smallest_uint", "[bit]") {
+    STATIC_REQUIRE(std::is_same_v<stdx::smallest_uint_t<8>, std::uint8_t>);
+    STATIC_REQUIRE(std::is_same_v<stdx::smallest_uint_t<9>, std::uint16_t>);
+    STATIC_REQUIRE(std::is_same_v<stdx::smallest_uint_t<16>, std::uint16_t>);
+    STATIC_REQUIRE(std::is_same_v<stdx::smallest_uint_t<17>, std::uint32_t>);
+    STATIC_REQUIRE(std::is_same_v<stdx::smallest_uint_t<32>, std::uint32_t>);
+    STATIC_REQUIRE(std::is_same_v<stdx::smallest_uint_t<33>, std::uint64_t>);
+    STATIC_REQUIRE(std::is_same_v<stdx::smallest_uint_t<64>, std::uint64_t>);
+    STATIC_REQUIRE(std::is_same_v<stdx::smallest_uint_t<65>, std::uint64_t>);
+}