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Export of internal Abseil changes.
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9c4ef32276054fba6a116c01cd4b3fd278f59ece by Andy Soffer <asoffer@google.com>:

Remove support for unused arbitrary-width output in FastUniformBits. Width
should be inferred from the requested return UIntType.

PiperOrigin-RevId: 257189319

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e3326329d02171a301cc3d6ae617ed448472b728 by Abseil Team <absl-team@google.com>:

Update comments to make clear that absl::Format(std::string *, ...) appends to the provided string.

PiperOrigin-RevId: 257058043

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e2096b06d714fba3ea2c885d670a42efd872765c by Xiaoyi Zhang <zhangxy@google.com>:

Fix compilation error on MSVC 2017. The root cause seems to be a compiler bug
in VS 2017 about pack expansion with multiple parameter packs, specifically `MakeVisitationMatrixImpl::Run` is triggering compiler error "error C3528: 'BoundIndices': the number of elements in this pack expansion does not match the number of elements in 'EndIndices'".
Work around this issue by using only one parameter pack `CurrIndices` in `MakeVisitationMatrixImpl::Run`.

PiperOrigin-RevId: 257040381

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9ab75ff27b2513583fffc1233e6568aa96be36f7 by Matt Calabrese <calabrese@google.com>:

Internal change.

PiperOrigin-RevId: 257039041
GitOrigin-RevId: 9c4ef32276054fba6a116c01cd4b3fd278f59ece
Change-Id: I5f708bb03aff93948502394a413260af2a8a273b
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@calabrese-google
Abseil Team authored and calabrese-google committed Jul 10, 2019
1 parent 3c98fcc commit 44efe96
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Showing 5 changed files with 50 additions and 211 deletions.
4 changes: 2 additions & 2 deletions absl/random/benchmarks.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -257,9 +257,9 @@ void BM_Thread(benchmark::State& state) {
BENCHMARK_TEMPLATE(BM_ShuffleReuse, Engine, 100); \
BENCHMARK_TEMPLATE(BM_ShuffleReuse, Engine, 1000); \
BENCHMARK_TEMPLATE(BM_Dist, Engine, \
absl::random_internal::FastUniformBits<uint32_t, 32>); \
absl::random_internal::FastUniformBits<uint32_t>); \
BENCHMARK_TEMPLATE(BM_Dist, Engine, \
absl::random_internal::FastUniformBits<uint64_t, 64>); \
absl::random_internal::FastUniformBits<uint64_t>); \
BENCHMARK_TEMPLATE(BM_Dist, Engine, std::uniform_int_distribution<int32_t>); \
BENCHMARK_TEMPLATE(BM_Dist, Engine, std::uniform_int_distribution<int64_t>); \
BENCHMARK_TEMPLATE(BM_Dist, Engine, \
Expand Down
52 changes: 17 additions & 35 deletions absl/random/internal/fast_uniform_bits.h
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Original file line number Diff line number Diff line change
Expand Up @@ -38,44 +38,27 @@ constexpr typename URBG::result_type constexpr_range() {
// from a type which conforms to the [rand.req.urbg] concept.
// Parameterized by:
// `UIntType`: the result (output) type
// `Width`: binary output width
//
// The std::independent_bits_engine [rand.adapt.ibits] adaptor can be
// instantiated from an existing generator through a copy or a move. It does
// not, however, facilitate the production of pseudorandom bits from an un-owned
// generator that will outlive the std::independent_bits_engine instance.
template <typename UIntType = uint64_t,
size_t Width = std::numeric_limits<UIntType>::digits>
template <typename UIntType = uint64_t>
class FastUniformBits {
static_assert(std::is_unsigned<UIntType>::value,
"Class-template FastUniformBits<> must be parameterized using "
"an unsigned type.");

// `kWidth` is the width, in binary digits, of the output. By default it is
// the number of binary digits in the `result_type`.
static constexpr size_t kWidth = Width;
static_assert(kWidth > 0,
"Class-template FastUniformBits<> Width argument must be > 0");

static_assert(kWidth <= std::numeric_limits<UIntType>::digits,
"Class-template FastUniformBits<> Width argument must be <= "
"width of UIntType.");

static constexpr bool kIsMaxWidth =
(kWidth >= std::numeric_limits<UIntType>::digits);

// Computes a mask of `n` bits for the `UIntType`.
static constexpr UIntType constexpr_mask(size_t n) {
return (UIntType(1) << n) - 1;
}
static constexpr size_t kWidth = std::numeric_limits<UIntType>::digits;

public:
using result_type = UIntType;

static constexpr result_type(min)() { return 0; }
static constexpr result_type(max)() {
return kIsMaxWidth ? (std::numeric_limits<result_type>::max)()
: constexpr_mask(kWidth);
return (std::numeric_limits<result_type>::max)();
}

template <typename URBG>
Expand Down Expand Up @@ -166,7 +149,6 @@ class FastUniformBitsURBGConstants {
// URBG::result_type values are combined into an output_value.
// Parameterized by the FastUniformBits parameters:
// `UIntType`: output type.
// `Width`: binary output width,
// `URNG`: The underlying UniformRandomNumberGenerator.
//
// The looping constants describe the sets of loop counters and mask values
Expand All @@ -177,10 +159,10 @@ class FastUniformBitsURBGConstants {
// bit per variate.
//
// See [rand.adapt.ibits] for more details on the use of these constants.
template <typename UIntType, size_t Width, typename URBG>
template <typename UIntType, typename URBG>
class FastUniformBitsLoopingConstants {
private:
static constexpr size_t kWidth = Width;
static constexpr size_t kWidth = std::numeric_limits<UIntType>::digits;
using urbg_result_type = typename URBG::result_type;
using uint_result_type = UIntType;

Expand Down Expand Up @@ -229,19 +211,19 @@ class FastUniformBitsLoopingConstants {
"Class-template FastUniformBitsLoopingConstants::kW0 too small.");
};

template <typename UIntType, size_t Width>
template <typename UIntType>
template <typename URBG>
typename FastUniformBits<UIntType, Width>::result_type
FastUniformBits<UIntType, Width>::operator()(
typename FastUniformBits<UIntType>::result_type
FastUniformBits<UIntType>::operator()(
URBG& g) { // NOLINT(runtime/references)
using constants = FastUniformBitsURBGConstants<URBG>;
return Generate(
g, std::integral_constant<bool, constants::kRangeMask >= (max)()>{});
}

template <typename UIntType, size_t Width>
template <typename UIntType>
template <typename URBG>
typename URBG::result_type FastUniformBits<UIntType, Width>::Variate(
typename URBG::result_type FastUniformBits<UIntType>::Variate(
URBG& g) { // NOLINT(runtime/references)
using constants = FastUniformBitsURBGConstants<URBG>;
if (constants::kPowerOfTwo) {
Expand All @@ -256,10 +238,10 @@ typename URBG::result_type FastUniformBits<UIntType, Width>::Variate(
return u;
}

template <typename UIntType, size_t Width>
template <typename UIntType>
template <typename URBG>
typename FastUniformBits<UIntType, Width>::result_type
FastUniformBits<UIntType, Width>::Generate(
typename FastUniformBits<UIntType>::result_type
FastUniformBits<UIntType>::Generate(
URBG& g, // NOLINT(runtime/references)
std::true_type /* avoid_looping */) {
// The width of the result_type is less than than the width of the random bits
Expand All @@ -268,18 +250,18 @@ FastUniformBits<UIntType, Width>::Generate(
return Variate(g) & (max)();
}

template <typename UIntType, size_t Width>
template <typename UIntType>
template <typename URBG>
typename FastUniformBits<UIntType, Width>::result_type
FastUniformBits<UIntType, Width>::Generate(
typename FastUniformBits<UIntType>::result_type
FastUniformBits<UIntType>::Generate(
URBG& g, // NOLINT(runtime/references)
std::false_type /* avoid_looping */) {
// The width of the result_type is wider than the number of random bits
// provided by URNG. Thus we merge several variates of URNG into the result
// using a shift and mask. The constants type generates the parameters used
// ensure that the bits are distributed across all the invocations of the
// underlying URNG.
using constants = FastUniformBitsLoopingConstants<UIntType, Width, URBG>;
using constants = FastUniformBitsLoopingConstants<UIntType, URBG>;

result_type s = 0;
for (size_t n = 0; n < constants::kN0; ++n) {
Expand Down
155 changes: 0 additions & 155 deletions absl/random/internal/fast_uniform_bits_test.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -45,57 +45,6 @@ TYPED_TEST(FastUniformBitsTypedTest, BasicTest) {
}
}

TEST(FastUniformBitsTest, TypeBoundaries32) {
// Tests that FastUniformBits can adapt to 32-bit boundaries.
absl::random_internal::FastUniformBits<uint32_t, 1> a;
absl::random_internal::FastUniformBits<uint32_t, 31> b;
absl::random_internal::FastUniformBits<uint32_t, 32> c;

{
std::mt19937 gen; // 32-bit
a(gen);
b(gen);
c(gen);
}

{
std::mt19937_64 gen; // 64-bit
a(gen);
b(gen);
c(gen);
}
}

TEST(FastUniformBitsTest, TypeBoundaries64) {
// Tests that FastUniformBits can adapt to 64-bit boundaries.
absl::random_internal::FastUniformBits<uint64_t, 1> a;
absl::random_internal::FastUniformBits<uint64_t, 31> b;
absl::random_internal::FastUniformBits<uint64_t, 32> c;
absl::random_internal::FastUniformBits<uint64_t, 33> d;
absl::random_internal::FastUniformBits<uint64_t, 63> e;
absl::random_internal::FastUniformBits<uint64_t, 64> f;

{
std::mt19937 gen; // 32-bit
a(gen);
b(gen);
c(gen);
d(gen);
e(gen);
f(gen);
}

{
std::mt19937_64 gen; // 64-bit
a(gen);
b(gen);
c(gen);
d(gen);
e(gen);
f(gen);
}
}

class UrngOddbits {
public:
using result_type = uint8_t;
Expand Down Expand Up @@ -135,18 +84,6 @@ TEST(FastUniformBitsTest, FastUniformBitsDetails) {
static_assert(constants::kRangeMask == 0x0f,
"constants::kRangeMask == false");
}
{
using looping = FastUniformBitsLoopingConstants<uint32_t, 31, Urng4bits>;
// To get 31 bits from a 4-bit generator, issue 8 calls and extract 4 bits
// per call on all except the first.
static_assert(looping::kN0 == 1, "looping::kN0");
static_assert(looping::kW0 == 3, "looping::kW0");
static_assert(looping::kM0 == 0x7, "looping::kM0");
// (The second set of calls, kN1, will not do anything.)
static_assert(looping::kN1 == 8, "looping::kN1");
static_assert(looping::kW1 == 4, "looping::kW1");
static_assert(looping::kM1 == 0xf, "looping::kM1");
}

// ~7-bit URBG
{
Expand All @@ -158,31 +95,6 @@ TEST(FastUniformBitsTest, FastUniformBitsDetails) {
static_assert(constants::kRangeMask == 0x7f,
"constants::kRangeMask == 0x7f");
}
{
using looping = FastUniformBitsLoopingConstants<uint64_t, 60, UrngOddbits>;
// To get 60 bits from a 7-bit generator, issue 10 calls and extract 6 bits
// per call, discarding the excess entropy.
static_assert(looping::kN0 == 10, "looping::kN0");
static_assert(looping::kW0 == 6, "looping::kW0");
static_assert(looping::kM0 == 0x3f, "looping::kM0");
// (The second set of calls, kN1, will not do anything.)
static_assert(looping::kN1 == 10, "looping::kN1");
static_assert(looping::kW1 == 7, "looping::kW1");
static_assert(looping::kM1 == 0x7f, "looping::kM1");
}
{
using looping = FastUniformBitsLoopingConstants<uint64_t, 63, UrngOddbits>;
// To get 63 bits from a 7-bit generator, issue 10 calls--the same as we
// would issue for 60 bits--however this time we use two groups. The first
// group (kN0) will issue 7 calls, extracting 6 bits per call.
static_assert(looping::kN0 == 7, "looping::kN0");
static_assert(looping::kW0 == 6, "looping::kW0");
static_assert(looping::kM0 == 0x3f, "looping::kM0");
// The second group (kN1) will issue 3 calls, extracting 7 bits per call.
static_assert(looping::kN1 == 10, "looping::kN1");
static_assert(looping::kW1 == 7, "looping::kW1");
static_assert(looping::kM1 == 0x7f, "looping::kM1");
}
}

TEST(FastUniformBitsTest, Urng4_VariousOutputs) {
Expand All @@ -192,94 +104,27 @@ TEST(FastUniformBitsTest, Urng4_VariousOutputs) {
Urng32bits urng32;

// 8-bit types
{
absl::random_internal::FastUniformBits<uint8_t, 1> fast1;
EXPECT_EQ(0x1, fast1(urng4));
EXPECT_EQ(0x1, fast1(urng32));
}
{
absl::random_internal::FastUniformBits<uint8_t, 2> fast2;
EXPECT_EQ(0x1, fast2(urng4));
EXPECT_EQ(0x1, fast2(urng32));
}

{
absl::random_internal::FastUniformBits<uint8_t, 4> fast4;
EXPECT_EQ(0x1, fast4(urng4));
EXPECT_EQ(0x1, fast4(urng32));
}
{
absl::random_internal::FastUniformBits<uint8_t, 6> fast6;
EXPECT_EQ(0x9, fast6(urng4)); // b001001 (2x3)
EXPECT_EQ(0x1, fast6(urng32));
}
{
absl::random_internal::FastUniformBits<uint8_t, 6> fast7;
EXPECT_EQ(0x9, fast7(urng4)); // b00001001 (1x4 + 1x3)
EXPECT_EQ(0x1, fast7(urng32));
}

{
absl::random_internal::FastUniformBits<uint8_t> fast8;
EXPECT_EQ(0x11, fast8(urng4));
EXPECT_EQ(0x1, fast8(urng32));
}

// 16-bit types
{
absl::random_internal::FastUniformBits<uint16_t, 10> fast10;
EXPECT_EQ(0x91, fast10(urng4)); // b 0010010001 (2x3 + 1x4)
EXPECT_EQ(0x1, fast10(urng32));
}
{
absl::random_internal::FastUniformBits<uint16_t, 11> fast11;
EXPECT_EQ(0x111, fast11(urng4));
EXPECT_EQ(0x1, fast11(urng32));
}
{
absl::random_internal::FastUniformBits<uint16_t, 12> fast12;
EXPECT_EQ(0x111, fast12(urng4));
EXPECT_EQ(0x1, fast12(urng32));
}

{
absl::random_internal::FastUniformBits<uint16_t> fast16;
EXPECT_EQ(0x1111, fast16(urng4));
EXPECT_EQ(0x1, fast16(urng32));
}

// 32-bit types
{
absl::random_internal::FastUniformBits<uint32_t, 21> fast21;
EXPECT_EQ(0x49111, fast21(urng4)); // b 001001001 000100010001 (3x3 + 3x4)
EXPECT_EQ(0x1, fast21(urng32));
}
{
absl::random_internal::FastUniformBits<uint32_t, 24> fast24;
EXPECT_EQ(0x111111, fast24(urng4));
EXPECT_EQ(0x1, fast24(urng32));
}

{
absl::random_internal::FastUniformBits<uint32_t> fast32;
EXPECT_EQ(0x11111111, fast32(urng4));
EXPECT_EQ(0x1, fast32(urng32));
}

// 64-bit types
{
absl::random_internal::FastUniformBits<uint64_t, 5> fast5;
EXPECT_EQ(0x9, fast5(urng4));
EXPECT_EQ(0x1, fast5(urng32));
}

{
absl::random_internal::FastUniformBits<uint64_t, 48> fast48;
EXPECT_EQ(0x111111111111, fast48(urng4));
// computes in 2 steps, should be 24 << 24
EXPECT_EQ(0x000001000001, fast48(urng32));
}

{
absl::random_internal::FastUniformBits<uint64_t> fast64;
EXPECT_EQ(0x1111111111111111, fast64(urng4));
Expand Down
2 changes: 1 addition & 1 deletion absl/strings/str_format.h
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Original file line number Diff line number Diff line change
Expand Up @@ -449,7 +449,7 @@ class FormatRawSink {
// additional arguments.
//
// By default, `std::string` and `std::ostream` are supported as destination
// objects.
// objects. If a `std::string` is used the formatted string is appended to it.
//
// `absl::Format()` is a generic version of `absl::StrFormat(), for custom
// sinks. The format string, like format strings for `StrFormat()`, is checked
Expand Down
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