ClickHouse

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#include <Functions/IFunction.h>
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#include <Functions/FunctionFactory.h>
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#include <Functions/FunctionHelpers.h>
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#include <DataTypes/DataTypesNumber.h>
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#include <Columns/ColumnsNumber.h>
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#include <Columns/ColumnDecimal.h>
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#include <base/extended_types.h>
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#include <base/itoa.h>
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namespace DB
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{
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namespace ErrorCodes
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{
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    extern const int ILLEGAL_TYPE_OF_ARGUMENT;
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    extern const int ILLEGAL_COLUMN;
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}
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namespace
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{
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template <typename T>
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int digits10(T x)
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{
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    if (x < 10ULL)
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        return 1;
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    if (x < 100ULL)
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        return 2;
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    if (x < 1000ULL)
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        return 3;
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    if (x < 1000000000000ULL)
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    {
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        if (x < 100000000ULL)
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        {
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            if (x < 1000000ULL)
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            {
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                if (x < 10000ULL)
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                    return 4;
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                else
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                    return 5 + (x >= 100000ULL);
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            }
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            return 7 + (x >= 10000000ULL);
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        }
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        if (x < 10000000000ULL)
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            return 9 + (x >= 1000000000ULL);
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        return 11 + (x >= 100000000000ULL);
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    }
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    return 12 + digits10(x / 1000000000000ULL);
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}
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/// Returns number of decimal digits you need to represent the value.
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/// For Decimal values takes in account their scales: calculates result over underlying int type which is (value * scale).
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/// countDigits(42) = 2, countDigits(42.000) = 5, countDigits(0.04200) = 4.
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/// I.e. you may check decimal overflow for Decimal64 with 'countDecimal(x) > 18'. It's a slow variant of isDecimalOverflow().
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class FunctionCountDigits : public IFunction
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{
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public:
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    static constexpr auto name = "countDigits";
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    static FunctionPtr create(ContextPtr)
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    {
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        return std::make_shared<FunctionCountDigits>();
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    }
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    String getName() const override { return name; }
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    bool useDefaultImplementationForConstants() const override { return true; }
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    size_t getNumberOfArguments() const override { return 1; }
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    bool isSuitableForShortCircuitArgumentsExecution(const DataTypesWithConstInfo & /*arguments*/) const override { return false; }
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    DataTypePtr getReturnTypeImpl(const DataTypes & arguments) const override
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    {
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        WhichDataType which_first(arguments[0]->getTypeId());
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        if (!which_first.isInt() && !which_first.isUInt() && !which_first.isDecimal())
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            throw Exception(ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT, "Illegal type {} of argument of function {}",
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                            arguments[0]->getName(), getName());
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        return std::make_shared<DataTypeUInt8>(); /// Up to 255 decimal digits.
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    }
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    ColumnPtr executeImpl(const ColumnsWithTypeAndName & arguments, const DataTypePtr &, size_t input_rows_count) const override
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    {
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        const auto & src_column = arguments[0];
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        if (!src_column.column)
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            throw Exception(ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT, "Illegal column while execute function {}", getName());
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        auto result_column = ColumnUInt8::create();
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        auto call = [&](const auto & types) -> bool
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        {
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            using Types = std::decay_t<decltype(types)>;
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            using Type = typename Types::RightType;
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            using ColVecType = ColumnVectorOrDecimal<Type>;
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            if (const ColVecType * col_vec = checkAndGetColumn<ColVecType>(src_column.column.get()))
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            {
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                execute<Type>(*col_vec, *result_column, input_rows_count);
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                return true;
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            }
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            throw Exception(ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT, "Illegal column while execute function {}", getName());
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        };
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        TypeIndex dec_type_idx = src_column.type->getTypeId();
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        if (!callOnBasicType<void, true, false, true, false>(dec_type_idx, call))
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            throw Exception(ErrorCodes::ILLEGAL_COLUMN, "Wrong call for {} with {}", getName(), src_column.type->getName());
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        return result_column;
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    }
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private:
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    template <typename T, typename ColVecType>
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    static void execute(const ColVecType & col, ColumnUInt8 & result_column, size_t rows_count)
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    {
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        using NativeT = make_unsigned_t<NativeType<T>>;
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        const auto & src_data = col.getData();
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        auto & dst_data = result_column.getData();
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        dst_data.resize(rows_count);
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        for (size_t i = 0; i < rows_count; ++i)
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        {
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            if constexpr (is_decimal<T>)
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            {
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                auto value = src_data[i].value;
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                if (unlikely(value < 0))
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                    dst_data[i] = digits10<NativeT>(-static_cast<NativeT>(value));
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                else
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                    dst_data[i] = digits10<NativeT>(value);
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            }
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            else
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            {
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                auto value = src_data[i];
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                if (unlikely(value < 0))
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                    dst_data[i] = digits10<NativeT>(-static_cast<NativeT>(value));
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                else
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                    dst_data[i] = digits10<NativeT>(value);
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            }
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        }
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    }
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};
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}
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REGISTER_FUNCTION(CountDigits)
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{
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    factory.registerFunction<FunctionCountDigits>();
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}
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}
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