minisketch.h

#ifndef _MINISKETCH_H_
#define _MINISKETCH_H_ 1

#include <stdint.h>
#include <stdlib.h>

#ifdef _MSC_VER
#  include <BaseTsd.h>
   typedef SSIZE_T ssize_t;
#else
#  include <unistd.h>
#endif

#ifndef MINISKETCH_API
# if defined(_WIN32)
#  ifdef MINISKETCH_BUILD
#   define MINISKETCH_API __declspec(dllexport)
#  else
#   define MINISKETCH_API
#  endif
# elif defined(__GNUC__) && (__GNUC__ >= 4) && defined(MINISKETCH_BUILD)
#  define MINISKETCH_API __attribute__ ((visibility ("default")))
# else
#  define MINISKETCH_API
# endif
#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
        {
            minisketch_destroy(ptr);
        }
    };

    std::unique_ptr<minisketch, Deleter> m_minisketch;

public:
    /** 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 (this != &sketch && 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(), result.data());
        if (ret == -1) return false;
        result.resize(ret);
        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());
        minisketch_serialize(m_minisketch.get(), result.data());
        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(obj.data())>::type (*)[], const unsigned char (*)[]>::value &&
            std::is_convertible<decltype(obj.size()), std::size_t>::value,
            std::nullptr_t
        >::type = nullptr) noexcept
    {
        assert(GetSerializedSize() == obj.size());
        minisketch_deserialize(m_minisketch.get(), obj.data());
        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, result.data());
        if (ret == -1) return {};
        result.resize(ret);
        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_