From b832dce8489ef7b6231384909fd9b68d5a5ff2b7 Mon Sep 17 00:00:00 2001 From: Abseil Team Date: Tue, 25 Feb 2020 22:27:31 +0100 Subject: Creation of LTS branch "lts_2020_02_25" - 0033c9ea91a52ade7c6b725aa2ef3cbe15463421 Fix build on FreeBSD/powerpc (#616) by kgotlinux <60880393+kgotlinux@users.noreply.github.com> - 0d5ce2797eb695aee7e019e25323251ef6ffc277 Export of internal Abseil changes by Abseil Team - b69c7d880caddfc25bf348dbcfe9d45fdd8bc6e6 Export of internal Abseil changes by Abseil Team - 2a5633fc077a58528cdbfe78720f3f6bfdc6044d Merge "Export of internal Abseil changes" by Xiaoyi Zhang - f9b3d6e493c1b6ab3dbdab71c5f8fa849db4abaf Add RISCV support to GetProgramCounter() (#621) by Khem Raj - 0232c87f21c26718aa3eb2d86678070f3b498a4e Add missing ABSL_HAVE_VDSO_SUPPORT conditional (#622) by Sinan Kaya <41809318+franksinankaya@users.noreply.github.com> - 3c814105108680997d0821077694f663693b5382 Export of internal Abseil changes by Abseil Team - c44657f55692eddf5504156645d1f4ec7b3acabd Export of internal Abseil changes by Abseil Team - 98eb410c93ad059f9bba1bf43f5bb916fc92a5ea Export of internal Abseil changes by Abseil Team - bf78e977309c4cb946914b456404141ddac1c302 Export of internal Abseil changes by Abseil Team - d95d1567165d449e4c213ea31a15cbb112a9865f Export of internal Abseil changes by Abseil Team - 24713a7036a81498334807fa5c7ad3cb7c643711 Export of internal Abseil changes by Abseil Team - 72382c21fefed981b4b8a2a1b82e2d231c2c2e39 Export of internal Abseil changes by Abseil Team - 08a7e7bf972c8451855a5022f2faf3d3655db015 Export of internal Abseil changes by Abseil Team - 36bcd9599b3f48c99357ba61cf33584889306d6a Fix pointer format specifier in documentation (#614) by Andre Nguyen - 0f86336b6939ea673cc1cbe29189286cae67d63a Export of internal Abseil changes by Abseil Team - c512f118dde6ffd51cb7d8ac8804bbaf4d266c3a Export of internal Abseil changes by Abseil Team - 37dd2562ec830d547a1524bb306be313ac3f2556 Export of internal Abseil changes by Abseil Team - 44427702614d7b86b064ba06a390f5eb2f85dbf6 fix: Add support for more ARM processors detection (#608) by Andre Nguyen - 159bf2bf6d1cc8087e02468d071e94d1177d1bae Export of internal Abseil changes by Abseil Team - a2e6adecc294dc4cd98cc285a9134ce58e0f2ad0 Use https links. 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-#ifndef ABSL_RANDOM_INTERNAL_DISTRIBUTION_IMPL_H_ -#define ABSL_RANDOM_INTERNAL_DISTRIBUTION_IMPL_H_ - -// This file contains some implementation details which are used by one or more -// of the absl random number distributions. - -#include -#include -#include -#include -#include -#include - -#if (defined(_WIN32) || defined(_WIN64)) && defined(_M_IA64) -#include // NOLINT(build/include_order) -#pragma intrinsic(_umul128) -#define ABSL_INTERNAL_USE_UMUL128 1 -#endif - -#include "absl/base/config.h" -#include "absl/base/internal/bits.h" -#include "absl/numeric/int128.h" -#include "absl/random/internal/fastmath.h" -#include "absl/random/internal/traits.h" - -namespace absl { -inline namespace lts_2019_08_08 { -namespace random_internal { - -// Creates a double from `bits`, with the template fields controlling the -// output. -// -// RandU64To is both more efficient and generates more unique values in the -// result interval than known implementations of std::generate_canonical(). -// -// The `Signed` parameter controls whether positive, negative, or both are -// returned (thus affecting the output interval). -// When Signed == SignedValueT, range is U(-1, 1) -// When Signed == NegativeValueT, range is U(-1, 0) -// When Signed == PositiveValueT, range is U(0, 1) -// -// When the `IncludeZero` parameter is true, the function may return 0 for some -// inputs, otherwise it never returns 0. -// -// The `ExponentBias` parameter determines the scale of the output range by -// adjusting the exponent. -// -// When a value in U(0,1) is required, use: -// RandU64ToDouble(); -// -// When a value in U(-1,1) is required, use: -// RandU64ToDouble() => U(-1, 1) -// This generates more distinct values than the mathematically equivalent -// expression `U(0, 1) * 2.0 - 1.0`, and is preferable. -// -// Scaling the result by powers of 2 (and avoiding a multiply) is also possible: -// RandU64ToDouble(); => U(0, 2) -// RandU64ToDouble(); => U(0, 0.5) -// - -// Tristate types controlling the output. -struct PositiveValueT {}; -struct NegativeValueT {}; -struct SignedValueT {}; - -// RandU64ToDouble is the double-result variant of RandU64To, described above. -template -inline double RandU64ToDouble(uint64_t bits) { - static_assert(std::is_same::value || - std::is_same::value || - std::is_same::value, - ""); - - // Maybe use the left-most bit for a sign bit. - uint64_t sign = std::is_same::value - ? 0x8000000000000000ull - : 0; // Sign bits. - - if (std::is_same::value) { - sign = bits & 0x8000000000000000ull; - bits = bits & 0x7FFFFFFFFFFFFFFFull; - } - if (IncludeZero) { - if (bits == 0u) return 0; - } - - // Number of leading zeros is mapped to the exponent: 2^-clz - int clz = base_internal::CountLeadingZeros64(bits); - // Shift number left to erase leading zeros. - bits <<= IncludeZero ? clz : (clz & 63); - - // Shift number right to remove bits that overflow double mantissa. The - // direction of the shift depends on `clz`. - bits >>= (64 - DBL_MANT_DIG); - - // Compute IEEE 754 double exponent. - // In the Signed case, bits is a 63-bit number with a 0 msb. Adjust the - // exponent to account for that. - const uint64_t exp = - (std::is_same::value ? 1023U : 1022U) + - static_cast(ExponentBias - clz); - constexpr int kExp = DBL_MANT_DIG - 1; - // Construct IEEE 754 double from exponent and mantissa. - const uint64_t val = sign | (exp << kExp) | (bits & ((1ULL << kExp) - 1U)); - - double res; - static_assert(sizeof(res) == sizeof(val), "double is not 64 bit"); - // Memcpy value from "val" to "res" to avoid aliasing problems. Assumes that - // endian-ness is same for double and uint64_t. - std::memcpy(&res, &val, sizeof(res)); - - return res; -} - -// RandU64ToFloat is the float-result variant of RandU64To, described above. -template -inline float RandU64ToFloat(uint64_t bits) { - static_assert(std::is_same::value || - std::is_same::value || - std::is_same::value, - ""); - - // Maybe use the left-most bit for a sign bit. - uint64_t sign = std::is_same::value - ? 0x80000000ul - : 0; // Sign bits. - - if (std::is_same::value) { - uint64_t a = bits & 0x8000000000000000ull; - sign = static_cast(a >> 32); - bits = bits & 0x7FFFFFFFFFFFFFFFull; - } - if (IncludeZero) { - if (bits == 0u) return 0; - } - - // Number of leading zeros is mapped to the exponent: 2^-clz - int clz = base_internal::CountLeadingZeros64(bits); - // Shift number left to erase leading zeros. - bits <<= IncludeZero ? clz : (clz & 63); - // Shift number right to remove bits that overflow double mantissa. The - // direction of the shift depends on `clz`. - bits >>= (64 - FLT_MANT_DIG); - - // Construct IEEE 754 float exponent. - // In the Signed case, bits is a 63-bit number with a 0 msb. Adjust the - // exponent to account for that. - const uint32_t exp = - (std::is_same::value ? 127U : 126U) + - static_cast(ExponentBias - clz); - constexpr int kExp = FLT_MANT_DIG - 1; - const uint32_t val = sign | (exp << kExp) | (bits & ((1U << kExp) - 1U)); - - float res; - static_assert(sizeof(res) == sizeof(val), "float is not 32 bit"); - // Assumes that endian-ness is same for float and uint32_t. - std::memcpy(&res, &val, sizeof(res)); - - return res; -} - -template -struct RandU64ToReal { - template - static inline Result Value(uint64_t bits) { - return RandU64ToDouble(bits); - } -}; - -template <> -struct RandU64ToReal { - template - static inline float Value(uint64_t bits) { - return RandU64ToFloat(bits); - } -}; - -inline uint128 MultiplyU64ToU128(uint64_t a, uint64_t b) { -#if defined(ABSL_HAVE_INTRINSIC_INT128) - return uint128(static_cast<__uint128_t>(a) * b); -#elif defined(ABSL_INTERNAL_USE_UMUL128) - // uint64_t * uint64_t => uint128 multiply using imul intrinsic on MSVC. - uint64_t high = 0; - const uint64_t low = _umul128(a, b, &high); - return absl::MakeUint128(high, low); -#else - // uint128(a) * uint128(b) in emulated mode computes a full 128-bit x 128-bit - // multiply. However there are many cases where that is not necessary, and it - // is only necessary to support a 64-bit x 64-bit = 128-bit multiply. This is - // for those cases. - const uint64_t a00 = static_cast(a); - const uint64_t a32 = a >> 32; - const uint64_t b00 = static_cast(b); - const uint64_t b32 = b >> 32; - - const uint64_t c00 = a00 * b00; - const uint64_t c32a = a00 * b32; - const uint64_t c32b = a32 * b00; - const uint64_t c64 = a32 * b32; - - const uint32_t carry = - static_cast(((c00 >> 32) + static_cast(c32a) + - static_cast(c32b)) >> - 32); - - return absl::MakeUint128(c64 + (c32a >> 32) + (c32b >> 32) + carry, - c00 + (c32a << 32) + (c32b << 32)); -#endif -} - -// wide_multiply multiplies two N-bit values to a 2N-bit result. -template -struct wide_multiply { - static constexpr size_t kN = std::numeric_limits::digits; - using input_type = UIntType; - using result_type = typename random_internal::unsigned_bits::type; - - static result_type multiply(input_type a, input_type b) { - return static_cast(a) * b; - } - - static input_type hi(result_type r) { return r >> kN; } - static input_type lo(result_type r) { return r; } - - static_assert(std::is_unsigned::value, - "Class-template wide_multiply<> argument must be unsigned."); -}; - -#ifndef ABSL_HAVE_INTRINSIC_INT128 -template <> -struct wide_multiply { - using input_type = uint64_t; - using result_type = uint128; - - static result_type multiply(uint64_t a, uint64_t b) { - return MultiplyU64ToU128(a, b); - } - - static uint64_t hi(result_type r) { return Uint128High64(r); } - static uint64_t lo(result_type r) { return Uint128Low64(r); } -}; -#endif - -} // namespace random_internal -} // inline namespace lts_2019_08_08 -} // namespace absl - -#endif // ABSL_RANDOM_INTERNAL_DISTRIBUTION_IMPL_H_ -- cgit v1.2.3