ClickHouse/src/Core/DecimalFunctions.h

#pragma once
// Moved Decimal-related functions out from Core/Types.h to reduce compilation time.

#include <Core/Types.h>
#include <Common/intExp.h>

#include <limits>

class DateLUTImpl;

namespace DB
{

namespace DecimalUtils
{

static constexpr size_t minPrecision() { return 1; }
template <typename T> static constexpr size_t maxPrecision() { return 0; }
template <> constexpr size_t maxPrecision<Decimal32>() { return 9; }
template <> constexpr size_t maxPrecision<Decimal64>() { return 18; }
template <> constexpr size_t maxPrecision<Decimal128>() { return 38; }

template <typename T> T scaleMultiplier(UInt32 scale);
template <> inline Int32 scaleMultiplier<Int32>(UInt32 scale) { return common::exp10_i32(scale); }
template <> inline Int64 scaleMultiplier<Int64>(UInt32 scale) { return common::exp10_i64(scale); }
template <> inline Int128 scaleMultiplier<Int128>(UInt32 scale) { return common::exp10_i128(scale); }

/** Components of DecimalX value:
 * whole - represents whole part of decimal, can be negatve or positive.
 * fractional - for fractional part of decimal, always positive.
 */
template <typename T>
struct DecimalComponents
{
    T whole;
    T fractional;
};

/** Make a decimal value from whole and fractional components with given scale multiplier.
 * where scale_multiplier = scaleMultiplier<T>(scale)
 * this is to reduce number of calls to scaleMultiplier when scale is known.
 *
 * Sign of `whole` controls sign of result: negative whole => negative result, positive whole => positive result.
 * Sign of `fractional` is expected to be positive, otherwise result is undefined.
 * If `scale` is to big (scale > maxPrecision<DecimalType::NativeType>), result is undefined.
 */
template <typename DecimalType>
DecimalType decimalFromComponentsWithMultiplier(const typename DecimalType::NativeType & whole,
                                                 const typename DecimalType::NativeType & fractional,
                                                 typename DecimalType::NativeType scale_multiplier)
{
    using T = typename DecimalType::NativeType;
    const auto fractional_sign = whole < 0 ? -1 : 1;

    const T value = whole * scale_multiplier + fractional_sign * (fractional % scale_multiplier);
    return DecimalType(value);
}

/** Make a decimal value from whole and fractional components with given scale.
 *
 * @see `decimalFromComponentsWithMultiplier` for details.
 */
template <typename DecimalType>
DecimalType decimalFromComponents(const typename DecimalType::NativeType & whole, const typename DecimalType::NativeType & fractional, UInt32 scale)
{
    using T = typename DecimalType::NativeType;

    return decimalFromComponentsWithMultiplier<DecimalType>(whole, fractional, scaleMultiplier<T>(scale));
}

/** Make a decimal value from whole and fractional components with given scale.
 * @see `decimalFromComponentsWithMultiplier` for details.
 */
template <typename DecimalType>
DecimalType decimalFromComponents(const DecimalComponents<typename DecimalType::NativeType> & components, UInt32 scale)
{
    return decimalFromComponents<DecimalType>(components.whole, components.fractional, scale);
}

/** Split decimal into whole and fractional parts with given scale_multiplier.
 * This is an optimization to reduce number of calls to scaleMultiplier on known scale.
 */
template <typename DecimalType>
DecimalComponents<typename DecimalType::NativeType> splitWithScaleMultiplier(const DecimalType & decimal, typename DecimalType::NativeType scale_multiplier)
{
    using T = typename DecimalType::NativeType;
    const auto whole = decimal.value / scale_multiplier;
    auto fractional = decimal.value % scale_multiplier;
    if (fractional < T(0))
        fractional *= T(-1);

    return {whole, fractional};
}

/// Split decimal into components: whole and fractional part, @see `DecimalComponents` for details.
template <typename DecimalType>
DecimalComponents<typename DecimalType::NativeType> split(const DecimalType & decimal, UInt32 scale)
{
    if (scale == 0)
    {
        return {decimal.value, 0};
    }
    return splitWithScaleMultiplier(decimal, scaleMultiplier<typename DecimalType::NativeType>(scale));
}

/** Get whole part from decimal.
 *
 * Sign of result follows sign of `decimal` value.
 * If scale is to big, result is undefined.
 */
template <typename DecimalType>
typename DecimalType::NativeType getWholePart(const DecimalType & decimal, size_t scale)
{
    if (scale == 0)
        return decimal.value;

    return decimal.value / scaleMultiplier<typename DecimalType::NativeType>(scale);
}

/** Get fractional part from decimal
 *
 * Result is always positive.
 * If scale is to big, result is undefined.
 */
template <typename DecimalType>
typename DecimalType::NativeType getFractionalPart(const DecimalType & decimal, size_t scale)
{
    using T = typename DecimalType::NativeType;

    if (scale == 0)
        return 0;

    T result = decimal.value;
    if (result < T(0))
        result *= T(-1);

    return result % scaleMultiplier<T>(scale);
}

}

}