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Commit 7f4fe64a by Abseil Team Committed by Gennadiy Rozental
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Export of internal Abseil changes 

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44efc1bb0e0a47eabf0569eaab81c66710d5b9c3 by Mark Barolak <mbar@google.com>:

Update "strings::Substitute" to "absl::Substitute" in the absl::Substitute error messages.

PiperOrigin-RevId: 282388042

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9ec7e9385f5469473f76857dc5b067d869bbc65b by Abseil Team <absl-team@google.com>:

Remove deprecated ExponentialBiased::Get()

PiperOrigin-RevId: 282045123
GitOrigin-RevId: 44efc1bb0e0a47eabf0569eaab81c66710d5b9c3
Change-Id: I915bf0ff5fa7ac2bd5f9fb653d1fbd9ece6af9fc
parent 16d9fd58
Showing with 18 additions and 58 deletions
absl/base/internal/exponential_biased.cc
......@@ -27,7 +27,16 @@
namespace absl {
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();
......@@ -63,47 +72,6 @@ int64_t ExponentialBiased::GetStride(int64_t mean) {
return GetSkipCount(mean - 1) + 1;
}
// 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::Get(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<uint32_t>(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<double>(std::numeric_limits<int64_t>::max() / 2)) {
// Assume huge values are bias neutral, retain bias for next call.
return std::numeric_limits<int64_t>::max() / 2;
}
int64_t value = std::max<int64_t>(1, std::round(interval));
bias_ = interval - value;
return value;
}
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
......
absl/base/internal/exponential_biased.h
......@@ -96,12 +96,6 @@ class ExponentialBiased {
// `GetSkipCount()` depends mostly on what best fits the use case.
int64_t GetStride(int64_t mean);
// Generates a rounded exponentially distributed random variable
// by rounding the value to the nearest integer.
// The result will be in the range [0, int64_t max / 2].
ABSL_DEPRECATED("Use GetSkipCount() or GetStride() instead")
int64_t Get(int64_t mean);
// Computes a random number in the range [0, 1<<(kPrngNumBits+1) - 1]
//
// This is public to enable testing.
......
absl/container/internal/hashtablez_sampler.cc
......@@ -196,12 +196,10 @@ HashtablezInfo* SampleSlow(int64_t* next_sample) {
return nullptr;
#else
bool first = *next_sample < 0;
*next_sample = g_exponential_biased_generator.Get(
*next_sample = g_exponential_biased_generator.GetStride(
g_hashtablez_sample_parameter.load(std::memory_order_relaxed));
// Small values of interval are equivalent to just sampling next time.
if (*next_sample < 1) {
*next_sample = 1;
}
ABSL_ASSERT(*next_sample >= 1);
// g_hashtablez_enabled can be dynamically flipped, we need to set a threshold
// low enough that we will start sampling in a reasonable time, so we just use
......
absl/strings/substitute.cc
......@@ -35,7 +35,7 @@ void SubstituteAndAppendArray(std::string* output, absl::string_view format,
if (i + 1 >= format.size()) {
#ifndef NDEBUG
ABSL_RAW_LOG(FATAL,
"Invalid strings::Substitute() format std::string: \"%s\".",
"Invalid absl::Substitute() format std::string: \"%s\".",
absl::CEscape(format).c_str());
#endif
return;
......@@ -45,7 +45,7 @@ void SubstituteAndAppendArray(std::string* output, absl::string_view format,
#ifndef NDEBUG
ABSL_RAW_LOG(
FATAL,
"Invalid strings::Substitute() format std::string: asked for \"$"
"Invalid absl::Substitute() format std::string: asked for \"$"
"%d\", but only %d args were given. Full format std::string was: "
"\"%s\".",
index, static_cast<int>(num_args), absl::CEscape(format).c_str());
......@@ -60,7 +60,7 @@ void SubstituteAndAppendArray(std::string* output, absl::string_view format,
} else {
#ifndef NDEBUG
ABSL_RAW_LOG(FATAL,
"Invalid strings::Substitute() format std::string: \"%s\".",
"Invalid absl::Substitute() format std::string: \"%s\".",
absl::CEscape(format).c_str());
#endif
return;
......
absl/strings/substitute_test.cc
......@@ -189,14 +189,14 @@ TEST(SubstituteTest, VectorBoolRef) {
TEST(SubstituteDeathTest, SubstituteDeath) {
EXPECT_DEBUG_DEATH(
static_cast<void>(absl::Substitute(absl::string_view("-$2"), "a", "b")),
"Invalid strings::Substitute\\(\\) format std::string: asked for \"\\$2\", "
"Invalid absl::Substitute\\(\\) format std::string: asked for \"\\$2\", "
"but only 2 args were given.");
EXPECT_DEBUG_DEATH(
static_cast<void>(absl::Substitute("-$z-")),
"Invalid strings::Substitute\\(\\) format std::string: \"-\\$z-\"");
"Invalid absl::Substitute\\(\\) format std::string: \"-\\$z-\"");
EXPECT_DEBUG_DEATH(
static_cast<void>(absl::Substitute("-$")),
"Invalid strings::Substitute\\(\\) format std::string: \"-\\$\"");
"Invalid absl::Substitute\\(\\) format std::string: \"-\\$\"");
}
#endif // GTEST_HAS_DEATH_TEST
......
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