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[vcpkg] Correct UInt128 code 😇 (#10583)

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* [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.
This commit is contained in:
nicole mazzuca 2020-04-09 14:11:53 -07:00 committed by GitHub
parent 0304c45315
commit 47a4913834
No known key found for this signature in database
GPG Key ID: 4AEE18F83AFDEB23
4 changed files with 150 additions and 73 deletions
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26
toolsrc/include/vcpkg/base/uint128.h Normal file
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@ -0,0 +1,26 @@
#pragma once
#include <stdint.h>
namespace vcpkg {
struct UInt128 {
UInt128() = default;
UInt128(uint64_t value) : bottom(value), top(0) {}
UInt128& operator<<=(int by) noexcept;
UInt128& operator>>=(int by) noexcept;
UInt128& operator+=(uint64_t lhs) noexcept;
uint64_t bottom_64_bits() const noexcept {
return bottom;
}
uint64_t top_64_bits() const noexcept {
return top;
}
private:
uint64_t bottom;
uint64_t top;
};
}

64
toolsrc/src/vcpkg-test/uint128.cpp Normal file
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@ -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);
}

78
toolsrc/src/vcpkg/base/hash.cpp
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@ -3,6 +3,7 @@
#include <vcpkg/base/hash.h>
#include <vcpkg/base/checks.h>
#include <vcpkg/base/uint128.h>
#include <vcpkg/base/strings.h>
#include <vcpkg/base/system.process.h>
#include <vcpkg/base/util.h>
@ -50,82 +51,13 @@ namespace vcpkg::Hash
}
}
namespace
{
struct UInt128
{
std::uint64_t top;
std::uint64_t bottom;
UInt128() = default;
UInt128(std::uint64_t value) : top(0), bottom(value) {}
UInt128& operator<<=(int by) noexcept
{
if (by == 0)
{
return *this;
}
if (by < 64)
{
top <<= by;
const auto shift_up = bottom >> (64 - by);
top |= shift_up;
bottom <<= by;
}
else
{
top = bottom;
top <<= (by - 64);
}
return *this;
}
UInt128& operator>>=(int by) noexcept
{
if (by == 0)
{
return *this;
}
if (by < 64)
{
bottom >>= by;
const auto shift_down = top << (64 - by);
bottom |= shift_down;
top >>= by;
}
else
{
bottom = top;
bottom >>= (by - 64);
}
return *this;
}
UInt128& operator+=(std::size_t lhs) noexcept
{
// bottom + lhs > uint64::max
if (bottom > std::numeric_limits<std::uint64_t>::max() - lhs)
{
top += 1;
}
bottom += lhs;
return *this;
}
};
}
template<class T>
void top_bits(T) = delete;
static constexpr uchar top_bits(uchar x) noexcept { return x; }
[[maybe_unused]] static constexpr uchar top_bits(std::uint32_t x) noexcept { return (x >> 24) & 0xFF; }
[[maybe_unused]] static constexpr uchar top_bits(std::uint64_t x) noexcept { return (x >> 56) & 0xFF; }
[[maybe_unused]] static constexpr uchar top_bits(UInt128 x) noexcept { return top_bits(x.top); }
[[maybe_unused]] static uchar top_bits(uchar x) noexcept { return x; }
[[maybe_unused]] static uchar top_bits(std::uint32_t x) noexcept { return (x >> 24) & 0xFF; }
[[maybe_unused]] static uchar top_bits(std::uint64_t x) noexcept { return (x >> 56) & 0xFF; }
[[maybe_unused]] static uchar top_bits(UInt128 x) noexcept { return top_bits(x.top_64_bits()); }
// treats UIntTy as big endian for the purpose of this mapping
template<class UIntTy>

55
toolsrc/src/vcpkg/base/uint128.cpp Normal file
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@ -0,0 +1,55 @@
#include <vcpkg/base/uint128.h>
#include <limits>
namespace vcpkg {
UInt128& UInt128::operator<<=(int by) noexcept {
if (by == 0) {
return *this;
}
if (by < 64) {
top <<= by;
const auto shift_up = bottom >> (64 - by);
top |= shift_up;
bottom <<= by;
} else {
top = bottom;
top <<= (by - 64);
bottom = 0;
}
return *this;
}
UInt128& UInt128::operator>>=(int by) noexcept {
if (by == 0) {
return *this;
}
if (by < 64) {
bottom >>= by;
const auto shift_down = top << (64 - by);
bottom |= shift_down;
top >>= by;
} else {
bottom = top;
bottom >>= (by - 64);
top = 0;
}
return *this;
}
UInt128& UInt128::operator+=(uint64_t rhs) noexcept {
// bottom + lhs > uint64::max
if (bottom > std::numeric_limits<uint64_t>::max() - rhs)
{
top += 1;
}
bottom += rhs;
return *this;
}
}