Program Listing for File utilities.h

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//==================================================================================
// BSD 2-Clause License
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// Copyright (c) 2014-2022, NJIT, Duality Technologies Inc. and other contributors
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#ifndef LBCRYPTO_UTILS_UTILITIES_H
#define LBCRYPTO_UTILS_UTILITIES_H

#include "config_core.h"
#include "utils/inttypes.h"

#include <cmath>
#include <climits>  // CHAR_BIT
#include <limits>   // std::numeric_limits
#include <string>
#include <type_traits>  // std::is_integral

namespace lbcrypto {

template <typename T, std::enable_if_t<std::is_integral_v<T>, bool> = true>
inline constexpr bool IsPowerOfTwo(T Input) {
    return Input && !(Input & (Input - 1));
}

// auxiliary function to replace a specific character "in" with another
// character "out"
std::string replaceChar(std::string str, char in, char out);

// Lazy Reduction functions: 64-bit multiplier and 128-bit Barrett reducer
// Originally proposed for BFVrnsB
inline uint64_t IsAdditionOverflow(uint64_t a, uint64_t b) {
    return (a + b) < b;
}

inline uint64_t AdditionWithCarryOut(uint64_t a, uint64_t b, uint64_t& c) {
    return (c = a + b) < b;
}

// TODO (dsuponit): the name of this function Max64BitValue() is misleading as it returns the largest value
// that can be converted from double to int64_t and not the max value of int64_t. The function must be renamed!!!
inline constexpr int64_t Max64BitValue() {
    return static_cast<int64_t>((uint64_t(1) << 63) - (uint64_t(1) << 9) - 1);
}

// TODO (dsuponit): the name of this function is64BitOverflow() is misleading as it checks if double can be
// converted to int64_t. The name should reflect that. Something like isConvertableToInt64(). The function must be renamed!!!
inline bool is64BitOverflow(double d) {
    return std::abs(d) > static_cast<double>(Max64BitValue());
}

#if NATIVEINT == 128 && !defined(__EMSCRIPTEN__)
inline constexpr __int128 Max128BitValue() {
    return static_cast<__int128>(((unsigned __int128)1 << 127) - ((unsigned __int128)1 << 73) - (unsigned __int128)1);
}

inline bool is128BitOverflow(double d) {
    return std::abs(d) > static_cast<double>(Max128BitValue());
}

enum { MAX_DOUBLE_PRECISION = 52 };
#endif

inline bool isConvertableToNativeInt(double d) {
    if constexpr (NATIVEINT == 32)
        return std::abs(d) <= static_cast<double>(std::numeric_limits<int32_t>::max());
    if constexpr (NATIVEINT == 64)
        return std::abs(d) <= static_cast<double>(Max64BitValue());
#if NATIVEINT == 128 && !defined(__EMSCRIPTEN__)
    if constexpr (NATIVEINT == 128)
        return std::abs(d) <= static_cast<double>(Max128BitValue());
#endif
}

}  // namespace lbcrypto

#endif