[vcpkg] Correct UInt128 code 😇 (#10583)

* [vcpkg] Correct UInt128 code 😇

`UInt128::operator<<(x, y)` should clear the bottom 64 bits of `x` if
`y >= 64`; however, we don't do this, and so we duplicate `x`'s bottom
bits into `x.top` instead of moving them. Similarly, we have the
opposite problem for `UInt128::operator>>`. This commit fixes these
latent bugs, which we weren't hitting because the thing we use them for
never actually shifts more than 64 bits.

1 files changed, 64 insertions, 0 deletions

diff --git a/toolsrc/src/vcpkg-test/uint128.cpp b/toolsrc/src/vcpkg-test/uint128.cpp
new file mode 100644
index 000000000..57d0169af
--- /dev/null
+++ b/toolsrc/src/vcpkg-test/uint128.cpp
@@ -0,0 +1,64 @@
+#include <catch2/catch.hpp>
+
+#include <vcpkg/base/uint128.h>
+
+TEST_CASE ("uint128 constructor and assign", "[uint128]") {
+	vcpkg::UInt128 x = 120;
+	REQUIRE(x.bottom_64_bits() == 120);
+	REQUIRE(x.top_64_bits() == 0);
+
+	x = 3201;
+	REQUIRE(x.bottom_64_bits() == 3201);
+	REQUIRE(x.top_64_bits() == 0);
+	
+	x = 0xFFFF'FFFF'FFFF'FFFF;
+	REQUIRE(x.bottom_64_bits() == 0xFFFF'FFFF'FFFF'FFFF);
+	REQUIRE(x.top_64_bits() == 0);
+}
+
+TEST_CASE ("uint128 add-assign", "[uint128]") {
+	vcpkg::UInt128 x = 0xFFFF'FFFF'FFFF'FFFF;
+	x += 1;
+	REQUIRE(x.bottom_64_bits() == 0);
+	REQUIRE(x.top_64_bits() == 1);
+}
+
+TEST_CASE ("uint128 shl-assign", "[uint128]") {
+	vcpkg::UInt128 x = 0xFFFF'FFFF'FFFF'FFFF;
+	x <<= 32;
+	REQUIRE(x.bottom_64_bits() == 0xFFFF'FFFF'0000'0000);
+	REQUIRE(x.top_64_bits() == 0x0000'0000'FFFF'FFFF);
+	
+	x <<= 60;
+	REQUIRE(x.bottom_64_bits() == 0);
+	REQUIRE(x.top_64_bits() == 0xFFFF'FFFF'F000'0000);
+
+	x = 1;
+	x <<= 96;
+	REQUIRE(x.bottom_64_bits() == 0);
+	REQUIRE(x.top_64_bits() == (uint64_t(1) << 32));
+}
+
+TEST_CASE ("uint128 shr-assign", "[uint128]") {
+	vcpkg::UInt128 x = 0xFFFF'FFFF'FFFF'FFFF;
+	x <<= 64;
+	REQUIRE(x.bottom_64_bits() == 0x0000'0000'0000'0000);
+	REQUIRE(x.top_64_bits() == 0xFFFF'FFFF'FFFF'FFFF);
+
+	x >>= 32;
+	REQUIRE(x.bottom_64_bits() == 0xFFFF'FFFF'0000'0000);
+	REQUIRE(x.top_64_bits() == 0x0000'0000'FFFF'FFFF);
+	
+	x >>= 60;
+	REQUIRE(x.bottom_64_bits() == 0x0000'000F'FFFF'FFFF);
+	REQUIRE(x.top_64_bits() == 0x0000'0000'0000'0000);
+
+	x = 0x8000'0000'0000'0000;
+	x <<= 64;
+	REQUIRE(x.bottom_64_bits() == 0);
+	REQUIRE(x.top_64_bits() == 0x8000'0000'0000'0000);
+
+	x >>= 96;
+	REQUIRE(x.bottom_64_bits() == (uint64_t(1) << 31));
+	REQUIRE(x.top_64_bits() == 0);
+}