Bitcoin Core integration/staging tree
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#ifndef _MINISKETCH_H_
#define _MINISKETCH_H_ 1
#include <stdint.h>
#include <stdlib.h>
#ifdef _MSC_VER
# include <BaseTsd.h>
typedef SSIZE_T ssize_t;
# include <unistd.h>
# if defined(_WIN32)
# define MINISKETCH_API __declspec(dllexport)
# else
# endif
# elif defined(__GNUC__) && (__GNUC__ >= 4) && defined(MINISKETCH_BUILD)
# define MINISKETCH_API __attribute__ ((visibility ("default")))
# else
# endif
#ifdef __cplusplus
# if __cplusplus >= 201103L
# include <memory>
# include <vector>
# include <cassert>
# if __cplusplus >= 201703L
# include <optional>
# endif // __cplusplus >= 201703L
# endif // __cplusplus >= 201103L
extern "C" {
#endif // __cplusplus
/** Opaque type for decoded sketches. */
typedef struct minisketch minisketch;
/** Determine whether support for elements of `bits` bits was compiled in. */
MINISKETCH_API int minisketch_bits_supported(uint32_t bits);
/** Determine the maximum number of implementations available.
* Multiple implementations may be available for a given element size, with
* different performance characteristics on different hardware.
* Each implementation is identified by a number from 0 to the output of this
* function call, inclusive. Note that not every combination of implementation
* and element size may exist (see further).
MINISKETCH_API uint32_t minisketch_implementation_max(void);
/** Determine if the a combination of bits and implementation number is available.
* Returns 1 if it is, 0 otherwise.
MINISKETCH_API int minisketch_implementation_supported(uint32_t bits, uint32_t implementation);
/** Construct a sketch for a given element size, implementation and capacity.
* If the combination of `bits` and `implementation` is unavailable, or when
* OOM occurs, NULL is returned. If minisketch_implementation_supported
* returns 1 for the specified bits and implementation, this will always succeed
* (except when allocation fails).
* If the result is not NULL, it must be destroyed using minisketch_destroy.
MINISKETCH_API minisketch* minisketch_create(uint32_t bits, uint32_t implementation, size_t capacity);
/** Get the element size of a sketch in bits. */
MINISKETCH_API uint32_t minisketch_bits(const minisketch* sketch);
/** Get the capacity of a sketch. */
MINISKETCH_API size_t minisketch_capacity(const minisketch* sketch);
/** Get the implementation of a sketch. */
MINISKETCH_API uint32_t minisketch_implementation(const minisketch* sketch);
/** Set the seed for randomizing algorithm choices to a fixed value.
* By default, sketches are initialized with a random seed. This is important
* to avoid scenarios where an attacker could force worst-case behavior.
* This function initializes the seed to a user-provided value (any 64-bit
* integer is acceptable, regardless of field size).
* When seed is -1, a fixed internal value with predictable behavior is
* used. It is only intended for testing.
MINISKETCH_API void minisketch_set_seed(minisketch* sketch, uint64_t seed);
/** Clone a sketch.
* The result must be destroyed using minisketch_destroy.
MINISKETCH_API minisketch* minisketch_clone(const minisketch* sketch);
/** Destroy a sketch.
* The pointer that was passed in may not be used anymore afterwards.
MINISKETCH_API void minisketch_destroy(minisketch* sketch);
/** Compute the size in bytes for serializing a given sketch. */
MINISKETCH_API size_t minisketch_serialized_size(const minisketch* sketch);
/** Serialize a sketch to bytes. */
MINISKETCH_API void minisketch_serialize(const minisketch* sketch, unsigned char* output);
/** Deserialize a sketch from bytes. */
MINISKETCH_API void minisketch_deserialize(minisketch* sketch, const unsigned char* input);
/** Add an element to a sketch.
* If the element to be added is too large for the sketch, the most significant
* bits of the element are dropped. More precisely, if the element size of
* `sketch` is b bits, then this function adds the unsigned integer represented
* by the b least significant bits of `element` to `sketch`.
* If the element to be added is 0 (after potentially dropping the most significant
* bits), then this function is a no-op. Sketches cannot contain an element with
* the value 0.
* Note that adding the same element a second time removes it again.
MINISKETCH_API void minisketch_add_uint64(minisketch* sketch, uint64_t element);
/** Merge the elements of another sketch into this sketch.
* After merging, `sketch` will contain every element that existed in one but not
* both of the input sketches. It can be seen as an exclusive or operation on
* the set elements. If the capacity of `other_sketch` is lower than `sketch`'s,
* merging reduces the capacity of `sketch` to that of `other_sketch`.
* This function returns the capacity of `sketch` after merging has been performed
* (where this capacity is at least 1), or 0 to indicate that merging has failed because
* the two input sketches differ in their element size or implementation. If 0 is
* returned, `sketch` (and its capacity) have not been modified.
* It is also possible to perform this operation directly on the serializations
* of two sketches with the same element size and capacity by performing a bitwise XOR
* of the serializations.
MINISKETCH_API size_t minisketch_merge(minisketch* sketch, const minisketch* other_sketch);
/** Decode a sketch.
* `output` is a pointer to an array of `max_element` uint64_t's, which will be
* filled with the elements in this sketch.
* The return value is the number of decoded elements, or -1 if decoding failed.
MINISKETCH_API ssize_t minisketch_decode(const minisketch* sketch, size_t max_elements, uint64_t* output);
/** Compute the capacity needed to achieve a certain rate of false positives.
* A sketch with capacity c and no more than c elements can always be decoded
* correctly. However, if it has more than c elements, or contains just random
* bytes, it is possible that it will still decode, but the result will be
* nonsense. This can be counteracted by increasing the capacity slightly.
* Given a field size bits, an intended number of elements that can be decoded
* max_elements, and a false positive probability of 1 in 2**fpbits, this
* function computes the necessary capacity. It is only guaranteed to be
* accurate up to fpbits=256.
MINISKETCH_API size_t minisketch_compute_capacity(uint32_t bits, size_t max_elements, uint32_t fpbits);
/** Compute what max_elements can be decoded for a certain rate of false positives.
* This is the inverse operation of minisketch_compute_capacity. It determines,
* given a field size bits, a capacity of a sketch, and an acceptable false
* positive probability of 1 in 2**fpbits, what the maximum allowed
* max_elements value is. If no value of max_elements would give the desired
* false positive probability, 0 is returned.
* Note that this is not an exact inverse of minisketch_compute_capacity. For
* example, with bits=32, fpbits=16, and max_elements=8,
* minisketch_compute_capacity will return 9, as capacity 8 would only have a
* false positive chance of 1 in 2^15.3. Increasing the capacity to 9 however
* decreases the fp chance to 1 in 2^47.3, enough for max_elements=9 (with fp
* chance of 1 in 2^18.5). Therefore, minisketch_compute_max_elements with
* capacity=9 will return 9.
MINISKETCH_API size_t minisketch_compute_max_elements(uint32_t bits, size_t capacity, uint32_t fpbits);
#ifdef __cplusplus
#if __cplusplus >= 201103L
/** Simple RAII C++11 wrapper around the minisketch API. */
class Minisketch
struct Deleter
void operator()(minisketch* ptr) const
std::unique_ptr<minisketch, Deleter> m_minisketch;
/** Check whether the library supports fields of the given size. */
static bool BitsSupported(uint32_t bits) noexcept { return minisketch_bits_supported(bits); }
/** Get the highest supported implementation number. */
static uint32_t MaxImplementation() noexcept { return minisketch_implementation_max(); }
/** Check whether the library supports fields with a given size and implementation number.
* If a particular field size `bits` is supported, implementation 0 is always supported for it.
* Higher implementation numbers may or may not be available as well, up to MaxImplementation().
static bool ImplementationSupported(uint32_t bits, uint32_t implementation) noexcept { return minisketch_implementation_supported(bits, implementation); }
/** Given field size and a maximum number of decodable elements n, compute what capacity c to
* use so that sketches with more elements than n have a chance no higher than 2^-fpbits of
* being decoded incorrectly (and will instead fail when decoding for up to n elements).
* See minisketch_compute_capacity for more details. */
static size_t ComputeCapacity(uint32_t bits, size_t max_elements, uint32_t fpbits) noexcept { return minisketch_compute_capacity(bits, max_elements, fpbits); }
/** Reverse operation of ComputeCapacity. See minisketch_compute_max_elements. */
static size_t ComputeMaxElements(uint32_t bits, size_t capacity, uint32_t fpbits) noexcept { return minisketch_compute_max_elements(bits, capacity, fpbits); }
/** Construct a clone of the specified sketch. */
Minisketch(const Minisketch& sketch) noexcept
if (sketch.m_minisketch) {
m_minisketch = std::unique_ptr<minisketch, Deleter>(minisketch_clone(sketch.m_minisketch.get()));
/** Make this Minisketch a clone of the specified one. */
Minisketch& operator=(const Minisketch& sketch) noexcept
if (sketch.m_minisketch) {
m_minisketch = std::unique_ptr<minisketch, Deleter>(minisketch_clone(sketch.m_minisketch.get()));
return *this;
/** Check whether this Minisketch object is valid. */
explicit operator bool() const noexcept { return bool{m_minisketch}; }
/** Construct an (invalid) Minisketch object. */
Minisketch() noexcept = default;
/** Move constructor. */
Minisketch(Minisketch&&) noexcept = default;
/** Move assignment. */
Minisketch& operator=(Minisketch&&) noexcept = default;
/** Construct a Minisketch object with the specified parameters.
* If bits is not BitsSupported(), or the combination of bits and capacity is not
* ImplementationSupported(), or OOM occurs internally, an invalid Minisketch
* object will be constructed. Use operator bool() to check that this isn't the
* case before performing any other operations. */
Minisketch(uint32_t bits, uint32_t implementation, size_t capacity) noexcept
m_minisketch = std::unique_ptr<minisketch, Deleter>(minisketch_create(bits, implementation, capacity));
/** Create a Minisketch object sufficiently large for the specified number of elements at given fpbits.
* It may construct an invalid object, which you may need to check for. */
static Minisketch CreateFP(uint32_t bits, uint32_t implementation, size_t max_elements, uint32_t fpbits) noexcept
return Minisketch(bits, implementation, ComputeCapacity(bits, max_elements, fpbits));
/** Return the field size for a (valid) Minisketch object. */
uint32_t GetBits() const noexcept { return minisketch_bits(m_minisketch.get()); }
/** Return the capacity for a (valid) Minisketch object. */
size_t GetCapacity() const noexcept { return minisketch_capacity(m_minisketch.get()); }
/** Return the implementation number for a (valid) Minisketch object. */
uint32_t GetImplementation() const noexcept { return minisketch_implementation(m_minisketch.get()); }
/** Set the seed for a (valid) Minisketch object. See minisketch_set_seed(). */
Minisketch& SetSeed(uint64_t seed) noexcept
minisketch_set_seed(m_minisketch.get(), seed);
return *this;
/** Add (or remove, if already present) an element to a (valid) Minisketch object.
* See minisketch_add_uint64(). */
Minisketch& Add(uint64_t element) noexcept
minisketch_add_uint64(m_minisketch.get(), element);
return *this;
/** Merge sketch into *this; both have to be valid Minisketch objects.
* See minisketch_merge for details. */
Minisketch& Merge(const Minisketch& sketch) noexcept
minisketch_merge(m_minisketch.get(), sketch.m_minisketch.get());
return *this;
/** Decode this (valid) Minisketch object into the result vector, up to as many elements as the
* vector's size permits. */
bool Decode(std::vector<uint64_t>& result) const
ssize_t ret = minisketch_decode(m_minisketch.get(), result.size(),;
if (ret == -1) return false;
return true;
/** Get the serialized size in bytes for this (valid) Minisketch object.. */
size_t GetSerializedSize() const noexcept { return minisketch_serialized_size(m_minisketch.get()); }
/** Serialize this (valid) Minisketch object as a byte vector. */
std::vector<unsigned char> Serialize() const
std::vector<unsigned char> result(GetSerializedSize());
return result;
/** Deserialize into this (valid) Minisketch from an object containing its bytes (which has data()
* and size() members). */
template<typename T>
Minisketch& Deserialize(
const T& obj,
typename std::enable_if<
std::is_convertible<typename std::remove_pointer<decltype(>::type (*)[], const unsigned char (*)[]>::value &&
std::is_convertible<decltype(obj.size()), std::size_t>::value,
>::type = nullptr) noexcept
assert(GetSerializedSize() == obj.size());
return *this;
#if __cplusplus >= 201703L
/** C++17 only: like Decode(), but up to a specified number of elements into an optional vector. */
std::optional<std::vector<uint64_t>> Decode(size_t max_elements) const
std::vector<uint64_t> result(max_elements);
ssize_t ret = minisketch_decode(m_minisketch.get(), max_elements,;
if (ret == -1) return {};
return result;
/** C++17 only: similar to Decode(), but with specified false positive probability. */
std::optional<std::vector<uint64_t>> DecodeFP(uint32_t fpbits) const
return Decode(ComputeMaxElements(GetBits(), GetCapacity(), fpbits));
#endif // __cplusplus >= 201703L
#endif // __cplusplus >= 201103L
#endif // __cplusplus
#endif // _MINISKETCH_H_