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Added another inaccurate method for reading floats #1665
This commit is contained in:
Alexey Milovidov
parent
f75ef123dc
commit
5e2f66954d
@ -9,31 +9,135 @@
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#include <IO/CompressedReadBuffer.h>
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int main(int, char **)
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using namespace DB;
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template <typename T>
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void readFloatTextFast(T & x, ReadBuffer & in)
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{
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static constexpr int MIN_EXPONENT = -323;
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static constexpr int MAX_EXPONENT = 308;
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static const T powers10[] =
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{
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1e-323, 1e-322, 1e-321, 1e-320, 1e-319, 1e-318, 1e-317, 1e-316, 1e-315, 1e-314, 1e-313, 1e-312, 1e-311,
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1e-310,1e-309,1e-308,1e-307,1e-306,1e-305,1e-304,1e-303,1e-302,1e-301,1e-300,1e-299,1e-298,1e-297,1e-296,1e-295,1e-294,1e-293,1e-292,1e-291,
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1e-290,1e-289,1e-288,1e-287,1e-286,1e-285,1e-284,1e-283,1e-282,1e-281,1e-280,1e-279,1e-278,1e-277,1e-276,1e-275,1e-274,1e-273,1e-272,1e-271,
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1e-270,1e-269,1e-268,1e-267,1e-266,1e-265,1e-264,1e-263,1e-262,1e-261,1e-260,1e-259,1e-258,1e-257,1e-256,1e-255,1e-254,1e-253,1e-252,1e-251,
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1e-250,1e-249,1e-248,1e-247,1e-246,1e-245,1e-244,1e-243,1e-242,1e-241,1e-240,1e-239,1e-238,1e-237,1e-236,1e-235,1e-234,1e-233,1e-232,1e-231,
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1e-230,1e-229,1e-228,1e-227,1e-226,1e-225,1e-224,1e-223,1e-222,1e-221,1e-220,1e-219,1e-218,1e-217,1e-216,1e-215,1e-214,1e-213,1e-212,1e-211,
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1e-210,1e-209,1e-208,1e-207,1e-206,1e-205,1e-204,1e-203,1e-202,1e-201,1e-200,1e-199,1e-198,1e-197,1e-196,1e-195,1e-194,1e-193,1e-192,1e-191,
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1e-190,1e-189,1e-188,1e-187,1e-186,1e-185,1e-184,1e-183,1e-182,1e-181,1e-180,1e-179,1e-178,1e-177,1e-176,1e-175,1e-174,1e-173,1e-172,1e-171,
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1e-170,1e-169,1e-168,1e-167,1e-166,1e-165,1e-164,1e-163,1e-162,1e-161,1e-160,1e-159,1e-158,1e-157,1e-156,1e-155,1e-154,1e-153,1e-152,1e-151,
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1e-150,1e-149,1e-148,1e-147,1e-146,1e-145,1e-144,1e-143,1e-142,1e-141,1e-140,1e-139,1e-138,1e-137,1e-136,1e-135,1e-134,1e-133,1e-132,1e-131,
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1e-130,1e-129,1e-128,1e-127,1e-126,1e-125,1e-124,1e-123,1e-122,1e-121,1e-120,1e-119,1e-118,1e-117,1e-116,1e-115,1e-114,1e-113,1e-112,1e-111,
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1e-110,1e-109,1e-108,1e-107,1e-106,1e-105,1e-104,1e-103,1e-102,1e-101,1e-100,1e-99,1e-98,1e-97,1e-96,1e-95,1e-94,1e-93,1e-92,1e-91,1e-90,
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1e-89,1e-88,1e-87,1e-86,1e-85,1e-84,1e-83,1e-82,1e-81,1e-80,1e-79,1e-78,1e-77,1e-76,1e-75,1e-74,1e-73,1e-72,1e-71,1e-70,
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1e-69,1e-68,1e-67,1e-66,1e-65,1e-64,1e-63,1e-62,1e-61,1e-60,1e-59,1e-58,1e-57,1e-56,1e-55,1e-54,1e-53,1e-52,1e-51,1e-50,
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1e-49,1e-48,1e-47,1e-46,1e-45,1e-44,1e-43,1e-42,1e-41,1e-40,1e-39,1e-38,1e-37,1e-36,1e-35,1e-34,1e-33,1e-32,1e-31,1e-30,
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1e-29,1e-28,1e-27,1e-26,1e-25,1e-24,1e-23,1e-22,1e-21,1e-20,1e-19,1e-18,1e-17,1e-16,1e-15,1e-14,1e-13,1e-12,1e-11,1e-10,
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1e-9,1e-8,1e-7,1e-6,1e-5,1e-4,1e-3,1e-2,1e-1,1e0,1e1,1e2,1e3,1e4,1e5,1e6,1e7,1e8,1e9,1e10,
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1e11,1e12,1e13,1e14,1e15,1e16,1e17,1e18,1e19,1e20,1e21,1e22,1e23,1e24,1e25,1e26,1e27,1e28,1e29,1e30,
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1e31,1e32,1e33,1e34,1e35,1e36,1e37,1e38,1e39,1e40,1e41,1e42,1e43,1e44,1e45,1e46,1e47,1e48,1e49,1e50,
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1e51,1e52,1e53,1e54,1e55,1e56,1e57,1e58,1e59,1e60,1e61,1e62,1e63,1e64,1e65,1e66,1e67,1e68,1e69,1e70,
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1e71,1e72,1e73,1e74,1e75,1e76,1e77,1e78,1e79,1e80,1e81,1e82,1e83,1e84,1e85,1e86,1e87,1e88,1e89,1e90,
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1e91,1e92,1e93,1e94,1e95,1e96,1e97,1e98,1e99,1e100,1e101,1e102,1e103,1e104,1e105,1e106,1e107,1e108,1e109,1e110,
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1e111,1e112,1e113,1e114,1e115,1e116,1e117,1e118,1e119,1e120,1e121,1e122,1e123,1e124,1e125,1e126,1e127,1e128,1e129,1e130,
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1e131,1e132,1e133,1e134,1e135,1e136,1e137,1e138,1e139,1e140,1e141,1e142,1e143,1e144,1e145,1e146,1e147,1e148,1e149,1e150,
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1e151,1e152,1e153,1e154,1e155,1e156,1e157,1e158,1e159,1e160,1e161,1e162,1e163,1e164,1e165,1e166,1e167,1e168,1e169,1e170,
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1e171,1e172,1e173,1e174,1e175,1e176,1e177,1e178,1e179,1e180,1e181,1e182,1e183,1e184,1e185,1e186,1e187,1e188,1e189,1e190,
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1e191,1e192,1e193,1e194,1e195,1e196,1e197,1e198,1e199,1e200,1e201,1e202,1e203,1e204,1e205,1e206,1e207,1e208,1e209,1e210,
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1e211,1e212,1e213,1e214,1e215,1e216,1e217,1e218,1e219,1e220,1e221,1e222,1e223,1e224,1e225,1e226,1e227,1e228,1e229,1e230,
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1e231,1e232,1e233,1e234,1e235,1e236,1e237,1e238,1e239,1e240,1e241,1e242,1e243,1e244,1e245,1e246,1e247,1e248,1e249,1e250,
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1e251,1e252,1e253,1e254,1e255,1e256,1e257,1e258,1e259,1e260,1e261,1e262,1e263,1e264,1e265,1e266,1e267,1e268,1e269,1e270,
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1e271,1e272,1e273,1e274,1e275,1e276,1e277,1e278,1e279,1e280,1e281,1e282,1e283,1e284,1e285,1e286,1e287,1e288,1e289,1e290,
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1e291,1e292,1e293,1e294,1e295,1e296,1e297,1e298,1e299,1e300,1e301,1e302,1e303,1e304,1e305,1e306,1e307,1e308
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};
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auto prev_count = in.count();
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Int64 before_point = 0;
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UInt64 after_point = 0;
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Int8 after_point_power = 0;
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Int16 exponent = 0;
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readIntText(before_point, in);
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if (checkChar('.', in))
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{
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auto after_point_count = in.count();
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readIntText(after_point, in);
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after_point_power = after_point_count - in.count();
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}
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if (checkChar('e', in) || checkChar('E', in))
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{
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readIntText(exponent, in);
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}
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x = before_point;
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if (after_point)
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x += after_point * powers10[after_point_power - MIN_EXPONENT];
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if (exponent)
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{
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if (unlikely(exponent < MIN_EXPONENT)) /// Note: there are some values below MIN_EXPONENT that is greater than zero.
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x *= 0; /// Multiplying to keep the sign of zero.
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else if (unlikely(exponent > MAX_EXPONENT))
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x *= std::numeric_limits<T>::infinity(); /// Multiplying to keep the sign of infinity.
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else
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x *= powers10[exponent - MIN_EXPONENT];
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}
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/// Denormals. At most one character is read and it is '-'. Note that it also can be '+', but we don't support this case.
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auto read_characters = in.count() - prev_count;
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if (unlikely(
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read_characters <= 1
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&& before_point == 0
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&& after_point_power == 0
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&& !in.eof()))
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{
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bool negative = read_characters == 1;
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if (*in.position() == 'i' || *in.position() == 'I')
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{
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assertInfinity(in);
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x = std::numeric_limits<T>::infinity();
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if (negative)
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x = -x;
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}
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else if (*in.position() == 'n' || *in.position() == 'N')
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{
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assertNaN(in);
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x = std::numeric_limits<T>::quiet_NaN();
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if (negative)
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x = -x;
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}
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}
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}
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int main(int, char **)
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try
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{
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DB::ReadBufferFromFile in("DevicePixelRatio");
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ReadBufferFromFileDescriptor in(STDIN_FILENO);
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DB::Float32 b = 0;
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Float64 sum = 0;
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Float64 x = 0;
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size_t i = 0;
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while (!in.eof())
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{
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DB::readFloatText(b, in);
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in.ignore();
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readFloatTextFast(x, in);
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assertChar('\n', in);
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++i;
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sum += x;
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}
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std::cout << b << std::endl;
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std::cout << i << std::endl;
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std::cout << sum << std::endl;
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return 0;
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}
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catch (const DB::Exception & e)
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catch (const Exception & e)
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{
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std::cerr << e.what() << ", " << e.displayText() << std::endl;
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return 1;
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}
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return 0;
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}
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