From 5aa5d282eac56a21e74611c1cdbaa97bb5db2dca Mon Sep 17 00:00:00 2001 From: Vincent Ambo Date: Tue, 8 Feb 2022 02:05:36 +0300 Subject: chore(3p/abseil_cpp): unvendor abseil_cpp we weren't actually using these sources anymore, okay? Change-Id: If701571d9716de308d3512e1eb22c35db0877a66 Reviewed-on: https://cl.tvl.fyi/c/depot/+/5248 Tested-by: BuildkiteCI Reviewed-by: grfn Autosubmit: tazjin --- .../absl/base/internal/exponential_biased.cc | 93 ---------------------- 1 file changed, 93 deletions(-) delete mode 100644 third_party/abseil_cpp/absl/base/internal/exponential_biased.cc (limited to 'third_party/abseil_cpp/absl/base/internal/exponential_biased.cc') diff --git a/third_party/abseil_cpp/absl/base/internal/exponential_biased.cc b/third_party/abseil_cpp/absl/base/internal/exponential_biased.cc deleted file mode 100644 index 1b30c061e3bd..000000000000 --- a/third_party/abseil_cpp/absl/base/internal/exponential_biased.cc +++ /dev/null @@ -1,93 +0,0 @@ -// Copyright 2019 The Abseil Authors. -// -// Licensed under the Apache License, Version 2.0 (the "License"); -// you may not use this file except in compliance with the License. -// You may obtain a copy of the License at -// -// https://www.apache.org/licenses/LICENSE-2.0 -// -// Unless required by applicable law or agreed to in writing, software -// distributed under the License is distributed on an "AS IS" BASIS, -// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. -// See the License for the specific language governing permissions and -// limitations under the License. - -#include "absl/base/internal/exponential_biased.h" - -#include - -#include -#include -#include -#include - -#include "absl/base/attributes.h" -#include "absl/base/optimization.h" - -namespace absl { -ABSL_NAMESPACE_BEGIN -namespace base_internal { - -// The algorithm generates a random number between 0 and 1 and applies the -// inverse cumulative distribution function for an exponential. Specifically: -// Let m be the inverse of the sample period, then the probability -// distribution function is m*exp(-mx) so the CDF is -// p = 1 - exp(-mx), so -// q = 1 - p = exp(-mx) -// log_e(q) = -mx -// -log_e(q)/m = x -// log_2(q) * (-log_e(2) * 1/m) = x -// In the code, q is actually in the range 1 to 2**26, hence the -26 below -int64_t ExponentialBiased::GetSkipCount(int64_t mean) { - if (ABSL_PREDICT_FALSE(!initialized_)) { - Initialize(); - } - - uint64_t rng = NextRandom(rng_); - rng_ = rng; - - // Take the top 26 bits as the random number - // (This plus the 1<<58 sampling bound give a max possible step of - // 5194297183973780480 bytes.) - // The uint32_t cast is to prevent a (hard-to-reproduce) NAN - // under piii debug for some binaries. - double q = static_cast(rng >> (kPrngNumBits - 26)) + 1.0; - // Put the computed p-value through the CDF of a geometric. - double interval = bias_ + (std::log2(q) - 26) * (-std::log(2.0) * mean); - // Very large values of interval overflow int64_t. To avoid that, we will - // cheat and clamp any huge values to (int64_t max)/2. This is a potential - // source of bias, but the mean would need to be such a large value that it's - // not likely to come up. For example, with a mean of 1e18, the probability of - // hitting this condition is about 1/1000. For a mean of 1e17, standard - // calculators claim that this event won't happen. - if (interval > static_cast(std::numeric_limits::max() / 2)) { - // Assume huge values are bias neutral, retain bias for next call. - return std::numeric_limits::max() / 2; - } - double value = std::round(interval); - bias_ = interval - value; - return value; -} - -int64_t ExponentialBiased::GetStride(int64_t mean) { - return GetSkipCount(mean - 1) + 1; -} - -void ExponentialBiased::Initialize() { - // We don't get well distributed numbers from `this` so we call NextRandom() a - // bunch to mush the bits around. We use a global_rand to handle the case - // where the same thread (by memory address) gets created and destroyed - // repeatedly. - ABSL_CONST_INIT static std::atomic global_rand(0); - uint64_t r = reinterpret_cast(this) + - global_rand.fetch_add(1, std::memory_order_relaxed); - for (int i = 0; i < 20; ++i) { - r = NextRandom(r); - } - rng_ = r; - initialized_ = true; -} - -} // namespace base_internal -ABSL_NAMESPACE_END -} // namespace absl -- cgit 1.4.1