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Simplify intx with some C++20 features #290

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merged 4 commits into from
Apr 22, 2023
Merged

Simplify intx with some C++20 features #290

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2e0f661
Use std::endian
chfast Mar 11, 2023
fa09613
Convert INTX_UNREACHABLE to intx::unreachable()
chfast Mar 11, 2023
8296dd7
Drop intx::is_constant_evaluated(), use std::
chfast Mar 11, 2023
ad44453
Use std::countl_zero() for intx::clz() implementation
chfast Mar 11, 2023
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121 changes: 27 additions & 94 deletions include/intx/intx.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -5,8 +5,10 @@
#pragma once

#include <algorithm>
#include <bit>
#include <cassert>
#include <climits>
#include <concepts>
#include <cstdint>
#include <cstring>
#include <limits>
Expand Down Expand Up @@ -37,17 +39,6 @@
#define __has_feature(NAME) 0
#endif

#if !defined(NDEBUG)
#define INTX_UNREACHABLE() assert(false)
#elif __has_builtin(__builtin_unreachable)
#define INTX_UNREACHABLE() __builtin_unreachable()
#elif defined(_MSC_VER)
#define INTX_UNREACHABLE() __assume(0)
#else
#define INTX_UNREACHABLE() (void)0
#endif


#if __has_builtin(__builtin_expect)
#define INTX_UNLIKELY(EXPR) __builtin_expect(bool{EXPR}, false)
#else
Expand All @@ -57,7 +48,7 @@
#if !defined(NDEBUG)
#define INTX_REQUIRE assert
#else
#define INTX_REQUIRE(X) (X) ? (void)0 : INTX_UNREACHABLE()
#define INTX_REQUIRE(X) (X) ? (void)0 : intx::unreachable()
#endif


Expand All @@ -70,6 +61,17 @@

namespace intx
{
/// Mark a possible code path as unreachable (invokes undefined behavior).
/// TODO(C++23): Use std::unreachable().
[[noreturn]] inline void unreachable() noexcept
{
#if __has_builtin(__builtin_unreachable)
__builtin_unreachable();
#elif defined(_MSC_VER)
__assume(false);
#endif
}

#if INTX_HAS_BUILTIN_INT128
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wpedantic" // Usage of __int128 triggers a pedantic warning.
Expand All @@ -80,15 +82,6 @@ using builtin_uint128 = unsigned __int128;
#pragma GCC diagnostic pop
#endif

constexpr bool byte_order_is_little_endian =
#if defined(__BYTE_ORDER__)
(__BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__);
#elif defined(_WIN32)
true; // On Windows assume little endian.
#else
#error "Unknown endianness"
#endif

template <unsigned N>
struct uint;

Expand Down Expand Up @@ -144,16 +137,6 @@ struct uint<128>
using uint128 = uint<128>;


inline constexpr bool is_constant_evaluated() noexcept
{
#if __has_builtin(__builtin_is_constant_evaluated) || (defined(_MSC_VER) && _MSC_VER >= 1925)
return __builtin_is_constant_evaluated();
#else
return true;
#endif
}


/// Contains result of add/sub/etc with a carry flag.
template <typename T>
struct result_with_carry
Expand All @@ -174,15 +157,15 @@ inline constexpr result_with_carry<uint64_t> addc(
uint64_t x, uint64_t y, bool carry = false) noexcept
{
#if __has_builtin(__builtin_addcll)
if (!is_constant_evaluated())
if (!std::is_constant_evaluated())
{
unsigned long long carryout = 0; // NOLINT(google-runtime-int)
const auto s = __builtin_addcll(x, y, carry, &carryout);
static_assert(sizeof(s) == sizeof(uint64_t));
return {s, static_cast<bool>(carryout)};
}
#elif __has_builtin(__builtin_ia32_addcarryx_u64)
if (!is_constant_evaluated())
if (!std::is_constant_evaluated())
{
unsigned long long s = 0; // NOLINT(google-runtime-int)
static_assert(sizeof(s) == sizeof(uint64_t));
Expand All @@ -203,15 +186,15 @@ inline constexpr result_with_carry<uint64_t> subc(
uint64_t x, uint64_t y, bool carry = false) noexcept
{
#if __has_builtin(__builtin_subcll)
if (!is_constant_evaluated())
if (!std::is_constant_evaluated())
{
unsigned long long carryout = 0; // NOLINT(google-runtime-int)
const auto d = __builtin_subcll(x, y, carry, &carryout);
static_assert(sizeof(d) == sizeof(uint64_t));
return {d, static_cast<bool>(carryout)};
}
#elif __has_builtin(__builtin_ia32_sbb_u64)
if (!is_constant_evaluated())
if (!std::is_constant_evaluated())
{
unsigned long long d = 0; // NOLINT(google-runtime-int)
static_assert(sizeof(d) == sizeof(uint64_t));
Expand Down Expand Up @@ -447,7 +430,7 @@ inline constexpr uint128 umul(uint64_t x, uint64_t y) noexcept
#if INTX_HAS_BUILTIN_INT128
return builtin_uint128{x} * builtin_uint128{y};
#elif defined(_MSC_VER) && _MSC_VER >= 1925 && defined(_M_X64)
if (!is_constant_evaluated())
if (!std::is_constant_evaluated())
{
unsigned __int64 hi = 0;
const auto lo = _umul128(x, y, &hi);
Expand Down Expand Up @@ -530,55 +513,9 @@ inline constexpr uint128& operator>>=(uint128& x, uint64_t shift) noexcept

/// @}


inline constexpr unsigned clz_generic(uint32_t x) noexcept
inline constexpr unsigned clz(std::unsigned_integral auto x) noexcept
{
unsigned n = 32;
for (int i = 4; i >= 0; --i)
{
const auto s = unsigned{1} << i;
const auto hi = x >> s;
if (hi != 0)
{
n -= s;
x = hi;
}
}
return n - x;
}

inline constexpr unsigned clz_generic(uint64_t x) noexcept
{
unsigned n = 64;
for (int i = 5; i >= 0; --i)
{
const auto s = unsigned{1} << i;
const auto hi = x >> s;
if (hi != 0)
{
n -= s;
x = hi;
}
}
return n - static_cast<unsigned>(x);
}

inline constexpr unsigned clz(uint32_t x) noexcept
{
#ifdef _MSC_VER
return clz_generic(x);
#else
return x != 0 ? unsigned(__builtin_clz(x)) : 32;
#endif
}

inline constexpr unsigned clz(uint64_t x) noexcept
{
#ifdef _MSC_VER
return clz_generic(x);
#else
return x != 0 ? unsigned(__builtin_clzll(x)) : 64;
#endif
return static_cast<unsigned>(std::countl_zero(x));
}

inline constexpr unsigned clz(uint128 x) noexcept
Expand All @@ -601,7 +538,7 @@ inline constexpr uint16_t bswap(uint16_t x) noexcept
return __builtin_bswap16(x);
#else
#ifdef _MSC_VER
if (!is_constant_evaluated())
if (!std::is_constant_evaluated())
return _byteswap_ushort(x);
#endif
return static_cast<uint16_t>((x << 8) | (x >> 8));
Expand All @@ -614,7 +551,7 @@ inline constexpr uint32_t bswap(uint32_t x) noexcept
return __builtin_bswap32(x);
#else
#ifdef _MSC_VER
if (!is_constant_evaluated())
if (!std::is_constant_evaluated())
return _byteswap_ulong(x);
#endif
const auto a = ((x << 8) & 0xFF00FF00) | ((x >> 8) & 0x00FF00FF);
Expand All @@ -628,7 +565,7 @@ inline constexpr uint64_t bswap(uint64_t x) noexcept
return __builtin_bswap64(x);
#else
#ifdef _MSC_VER
if (!is_constant_evaluated())
if (!std::is_constant_evaluated())
return _byteswap_uint64(x);
#endif
const auto a = ((x << 8) & 0xFF00FF00FF00FF00) | ((x >> 8) & 0x00FF00FF00FF00FF);
Expand Down Expand Up @@ -1596,11 +1533,7 @@ namespace internal
inline constexpr unsigned clz_nonzero(uint64_t x) noexcept
{
INTX_REQUIRE(x != 0);
#ifdef _MSC_VER
return clz_generic(x);
#else
return unsigned(__builtin_clzll(x));
#endif
return static_cast<unsigned>(std::countl_zero(x));
}

template <unsigned M, unsigned N>
Expand Down Expand Up @@ -1927,7 +1860,7 @@ inline constexpr uint512 operator"" _u512(const char* s)
template <typename T>
inline constexpr T to_little_endian(const T& x) noexcept
{
if constexpr (byte_order_is_little_endian)
if constexpr (std::endian::native == std::endian::little)
return x;
else if constexpr (std::is_integral_v<T>)
return bswap(x);
Expand All @@ -1945,7 +1878,7 @@ inline constexpr T to_little_endian(const T& x) noexcept
template <typename T>
inline constexpr T to_big_endian(const T& x) noexcept
{
if constexpr (byte_order_is_little_endian)
if constexpr (std::endian::native == std::endian::little)
return bswap(x);
else if constexpr (std::is_integral_v<T>)
return x;
Expand Down
1 change: 0 additions & 1 deletion test/benchmarks/CMakeLists.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -9,7 +9,6 @@ find_package(GMP REQUIRED)

add_executable(intx-bench
../experimental/addmod.hpp
bench_builtins.cpp
bench_div.cpp
bench_int128.cpp
benchmarks.cpp
Expand Down
32 changes: 0 additions & 32 deletions test/benchmarks/bench_builtins.cpp
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