From 078b89b3c046d230ef3ad39494e5852184eb528b Mon Sep 17 00:00:00 2001 From: Abseil Team Date: Wed, 23 Oct 2019 19:35:39 -0700 Subject: Export of internal Abseil changes -- e54b9c7bbb0c58475676c268e2e19c69f4bce48a by Jorg Brown : Tweak ABSL_PREDICT_TRUE slightly, for better code on some platforms and/or optimization levels. "false || (x)" is more verbose than "!!(x)", but ultimately more efficient. For example, given this code: void InitIfNecessary() { if (ABSL_PREDICT_TRUE(NeedsInit())) { SlowInitIfNecessary(); } } Clang with default optimization level will produce: Before this CL After this CL InitIfNecessary: InitIfNecessary: push rbp push rbp mov rbp, rsp mov rbp, rsp call NeedsInit call NeedsInit xor al, -1 xor al, -1 test al, 1 test al, 1 jne .LBB2_1 jne .LBB3_1 jmp .LBB2_2 jmp .LBB3_2 .LBB2_1: .LBB3_1: call SlowInitIfNecessary call SlowInitIfNecessary .LBB2_2: .LBB3_2: pop rbp pop rbp ret ret PiperOrigin-RevId: 276401386 -- 0a3c4dfd8342bf2b1b11a87f1c662c883f73cab7 by Abseil Team : Fix comment nit: sem_open => sem_init. The code calls sem_init, not sem_open, to initialize an unnamed semaphore. (sem_open creates or opens a named semaphore.) PiperOrigin-RevId: 276344072 -- b36a664e9459057509a90e83d3482e1d3a4c44c7 by Abseil Team : Fix typo in flat_hash_map.h: exchaged -> exchanged PiperOrigin-RevId: 276295792 -- 7bbd8d18276eb110c8335743e35fceb662ddf3d6 by Samuel Benzaquen : Add assertions to verify use of iterators. PiperOrigin-RevId: 276283300 -- 677398a8ffcb1f59182cffe57a4fe7ff147a0404 by Laramie Leavitt : Migrate distribution_impl.h/cc to generate_real.h/cc. Combine the methods RandU64To into a single method: GenerateRealFromBits(). Remove rejection sampling from absl::uniform_real_distribution. PiperOrigin-RevId: 276158675 -- c60c9d11d24b0c546329d998e78e15a84b3153f5 by Abseil Team : Internal change PiperOrigin-RevId: 276126962 -- 4c840cab6a8d86efa29b397cafaf7520eece68cc by Andy Soffer : Update CMakeLists.txt to address https://github.com/abseil/abseil-cpp/issues/365. This does not cover every platform, but it does at least address the first-order issue of assuming gcc implies x86. PiperOrigin-RevId: 276116253 -- 98da366e6b5d51afe5d7ac6722126aca23d85ee6 by Abseil Team : Internal change PiperOrigin-RevId: 276097452 GitOrigin-RevId: e54b9c7bbb0c58475676c268e2e19c69f4bce48a Change-Id: I02d84454bb71ab21ad3d39650acf6cc6e36f58d7 --- absl/random/gaussian_distribution.h | 22 +++++++++++++++++----- 1 file changed, 17 insertions(+), 5 deletions(-) (limited to 'absl/random/gaussian_distribution.h') diff --git a/absl/random/gaussian_distribution.h b/absl/random/gaussian_distribution.h index 1d1347bc..c299e944 100644 --- a/absl/random/gaussian_distribution.h +++ b/absl/random/gaussian_distribution.h @@ -28,8 +28,8 @@ #include #include -#include "absl/random/internal/distribution_impl.h" #include "absl/random/internal/fast_uniform_bits.h" +#include "absl/random/internal/generate_real.h" #include "absl/random/internal/iostream_state_saver.h" namespace absl { @@ -207,12 +207,18 @@ namespace random_internal { template inline double gaussian_distribution_base::zignor_fallback(URBG& g, bool neg) { + using random_internal::GeneratePositiveTag; + using random_internal::GenerateRealFromBits; + // This fallback path happens approximately 0.05% of the time. double x, y; do { // kRInv = 1/r, U(0, 1) - x = kRInv * std::log(RandU64ToDouble(fast_u64_(g))); - y = -std::log(RandU64ToDouble(fast_u64_(g))); + x = kRInv * + std::log(GenerateRealFromBits( + fast_u64_(g))); + y = -std::log( + GenerateRealFromBits(fast_u64_(g))); } while ((y + y) < (x * x)); return neg ? (x - kR) : (kR - x); } @@ -220,6 +226,10 @@ inline double gaussian_distribution_base::zignor_fallback(URBG& g, bool neg) { template inline double gaussian_distribution_base::zignor( URBG& g) { // NOLINT(runtime/references) + using random_internal::GeneratePositiveTag; + using random_internal::GenerateRealFromBits; + using random_internal::GenerateSignedTag; + while (true) { // We use a single uint64_t to generate both a double and a strip. // These bits are unused when the generated double is > 1/2^5. @@ -227,7 +237,8 @@ inline double gaussian_distribution_base::zignor( // values (those smaller than 1/2^5, which all end up on the left tail). uint64_t bits = fast_u64_(g); int i = static_cast(bits & kMask); // pick a random strip - double j = RandU64ToDouble(bits); // U(-1, 1) + double j = GenerateRealFromBits( + bits); // U(-1, 1) const double x = j * zg_.x[i]; // Retangular box. Handles >97% of all cases. @@ -244,7 +255,8 @@ inline double gaussian_distribution_base::zignor( } // i > 0: Wedge samples using precomputed values. - double v = RandU64ToDouble(fast_u64_(g)); // U(0, 1) + double v = GenerateRealFromBits( + fast_u64_(g)); // U(0, 1) if ((zg_.f[i + 1] + v * (zg_.f[i] - zg_.f[i + 1])) < std::exp(-0.5 * x * x)) { return x; -- cgit v1.2.3