diff --git a/docs/decfloat.md b/docs/decfloat.md
index 3bb60e305..4aacbce97 100644
--- a/docs/decfloat.md
+++ b/docs/decfloat.md
@@ -2,6 +2,25 @@
 
 `DECFLOAT(16)` and `DECFLOAT(34)` from Firebird 4 is handled by `FbDecFloat` type. `FbDecFloat` can be used as parameter value for `FbParameter`.
 
+### Values are never rounded silently
+
+`DECFLOAT(16)` holds 16 significant digits and `DECFLOAT(34)` holds 34. A value that cannot be represented exactly in the precision or exponent range of the target (for example a 17 digit value passed to a `DECFLOAT(16)` parameter) throws `OverflowException`. Values that only need trailing zeros removed or the exponent adjusted (e.g. `1E384` in `DECFLOAT(16)`) are accepted.
+
+### Other .NET types
+
+Parameters: besides `FbDecFloat`, a `DECFLOAT` parameter accepts `decimal`, `double`, `float`, the integral types and `BigInteger`:
+
+* `decimal` is converted exactly, including its scale (`1.10m` stays `1.10`).
+* `double` and `float` are converted to the shortest decimal that converts back to the same binary value (`0.1` is `0.1`, `0.1 + 0.2` is `0.30000000000000004`), which may have up to 17 significant digits.
+
+Reading a `DECFLOAT` column:
+
+* `GetDecimal` is exact; it throws `OverflowException` when the value cannot be represented exactly as `decimal` (too large, too many digits, NaN or infinity).
+* `GetDouble` and `GetFloat` return the nearest value (NaN and infinities are mapped).
+* `GetInt16`, `GetInt32`, `GetInt64` and `GetByte` round to the nearest integer, ties to even, and throw `OverflowException` when out of range.
+
+`FbDecFloat` has explicit conversions from and to `decimal`, `double` and `float`, with the same rules.
+
 ### Examples
 
 Examples can be found in [`FbDecFloat16SupportTests`](../src/FirebirdSql.Data.FirebirdClient.Tests/FbDecFloat16SupportTests.cs) and [`FbDecFloat34SupportTests`](../src/FirebirdSql.Data.FirebirdClient.Tests/FbDecFloat34SupportTests.cs).
diff --git a/src/FirebirdSql.Data.FirebirdClient.Tests/DecimalCodecTests.cs b/src/FirebirdSql.Data.FirebirdClient.Tests/DecimalCodecTests.cs
new file mode 100644
index 000000000..3c222bd07
--- /dev/null
+++ b/src/FirebirdSql.Data.FirebirdClient.Tests/DecimalCodecTests.cs
@@ -0,0 +1,106 @@
+/*
+ *    The contents of this file are subject to the Initial
+ *    Developer's Public License Version 1.0 (the "License");
+ *    you may not use this file except in compliance with the
+ *    License. You may obtain a copy of the License at
+ *    https://github.com/FirebirdSQL/NETProvider/raw/master/license.txt.
+ *
+ *    Software distributed under the License is distributed on
+ *    an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, either
+ *    express or implied. See the License for the specific
+ *    language governing rights and limitations under the License.
+ *
+ *    All Rights Reserved.
+ */
+
+//$Authors = F.D.Castel
+
+using System;
+using System.Numerics;
+using FirebirdSql.Data.Common;
+using FirebirdSql.Data.TestsBase;
+using FirebirdSql.Data.Types;
+using NUnit.Framework;
+
+namespace FirebirdSql.Data.FirebirdClient.Tests;
+
+[NoServerCategory]
+public class DecimalCodecTests
+{
+	static readonly object[] RepresentableDecFloat16Values = new object[]
+	{
+		new FbDecFloat(BigInteger.Parse("9999999999999999"), 369),
+		new FbDecFloat(BigInteger.Parse("-9999999999999999"), 369),
+		new FbDecFloat(1, -398),
+		new FbDecFloat(-1, -398),
+		// representable only after normalization
+		new FbDecFloat(1, 384),
+		new FbDecFloat(-1, 384),
+		new FbDecFloat(BigInteger.Parse("100000000000000000000"), -20),
+		new FbDecFloat(BigInteger.Parse("12345678901234560"), 0),
+		new FbDecFloat(100, -400),
+		new FbDecFloat(0, 1000),
+		new FbDecFloat(0, -1000),
+	};
+	[TestCaseSource(nameof(RepresentableDecFloat16Values))]
+	public void DecFloat16EncodesRepresentableValueExactly(FbDecFloat value)
+	{
+		var result = DecimalCodec.DecFloat16.ParseBytes(DecimalCodec.DecFloat16.EncodeDecimal(value));
+		Assert.AreEqual(value, result);
+	}
+
+	static readonly object[] RepresentableDecFloat34Values = new object[]
+	{
+		new FbDecFloat(BigInteger.Parse("9999999999999999999999999999999999"), 6111),
+		new FbDecFloat(1, -6176),
+		// representable only after normalization
+		new FbDecFloat(1, 6144),
+		new FbDecFloat(BigInteger.Parse("12345678901234567890123456789012340"), 0),
+		new FbDecFloat(BigInteger.Parse("-12345678901234567890123456789012340000"), -40),
+		new FbDecFloat(1000, -6179),
+		new FbDecFloat(0, int.MaxValue),
+		new FbDecFloat(0, int.MinValue),
+	};
+	[TestCaseSource(nameof(RepresentableDecFloat34Values))]
+	public void DecFloat34EncodesRepresentableValueExactly(FbDecFloat value)
+	{
+		var result = DecimalCodec.DecFloat34.ParseBytes(DecimalCodec.DecFloat34.EncodeDecimal(value));
+		Assert.AreEqual(value, result);
+	}
+
+	[Test]
+	public void ZeroExponentIsClamped()
+	{
+		var result = DecimalCodec.DecFloat16.ParseBytes(DecimalCodec.DecFloat16.EncodeDecimal(new FbDecFloat(0, 1000)));
+		Assert.AreEqual(369, result.Exponent);
+	}
+
+	static readonly object[] UnrepresentableDecFloat16Values = new object[]
+	{
+		new FbDecFloat(BigInteger.Parse("30000000000000004"), -17),
+		new FbDecFloat(BigInteger.Parse("-12345678901234567"), 0),
+		new FbDecFloat(1, 385),
+		new FbDecFloat(BigInteger.Parse("9999999999999999"), 370),
+		new FbDecFloat(1, -399),
+		new FbDecFloat(15, -400),
+		new FbDecFloat(1, int.MaxValue),
+		new FbDecFloat(1, int.MinValue),
+	};
+	[TestCaseSource(nameof(UnrepresentableDecFloat16Values))]
+	public void DecFloat16ThrowsInsteadOfRounding(FbDecFloat value)
+	{
+		Assert.Throws<OverflowException>(() => DecimalCodec.DecFloat16.EncodeDecimal(value));
+	}
+
+	static readonly object[] UnrepresentableDecFloat34Values = new object[]
+	{
+		new FbDecFloat(BigInteger.Parse("12345678901234567890123456789012345"), 0),
+		new FbDecFloat(1, 6145),
+		new FbDecFloat(1, -6177),
+	};
+	[TestCaseSource(nameof(UnrepresentableDecFloat34Values))]
+	public void DecFloat34ThrowsInsteadOfRounding(FbDecFloat value)
+	{
+		Assert.Throws<OverflowException>(() => DecimalCodec.DecFloat34.EncodeDecimal(value));
+	}
+}
diff --git a/src/FirebirdSql.Data.FirebirdClient.Tests/FbDecFloat16SupportTests.cs b/src/FirebirdSql.Data.FirebirdClient.Tests/FbDecFloat16SupportTests.cs
index 1fba53622..449d625f5 100644
--- a/src/FirebirdSql.Data.FirebirdClient.Tests/FbDecFloat16SupportTests.cs
+++ b/src/FirebirdSql.Data.FirebirdClient.Tests/FbDecFloat16SupportTests.cs
@@ -16,6 +16,7 @@
 //$Authors = Jiri Cincura (jiri@cincura.net)
 
 using System;
+using System.Globalization;
 using System.Numerics;
 using System.Threading.Tasks;
 using FirebirdSql.Data.TestsBase;
@@ -63,8 +64,25 @@ public override async Task SetUp()
 			new object[] { new FbDecFloat(-10, 34), "-100000000000000000000000000000000000" },
 			new object[] { new FbDecFloat(BigInteger.Parse("123000000001"), -10), "123.000000001E-1" },
 			new object[] { new FbDecFloat(BigInteger.Parse("-123000000001"), -10), "-123.000000001E-1" },
+			new object[] { new FbDecFloat(1, 384), "1E384" },
+			new object[] { new FbDecFloat(BigInteger.Parse("100000000000000000000"), -20), "1" },
+			new object[] { new FbDecFloat(100, -400), "1E-398" },
+			new object[] { (FbDecFloat)2.0, "2" },
+			new object[] { (FbDecFloat)1e-20, "1E-20" },
+			new object[] { (FbDecFloat)2.5f, "2.5" },
+			new object[] { (FbDecFloat)100m, "100" },
+			new object[] { (FbDecFloat)1.10m, "1.10" },
 		};
 
+	static readonly object[] UnrepresentableValues = new object[]
+	{
+		new FbDecFloat(BigInteger.Parse("30000000000000004"), -17),
+		new FbDecFloat(1, 385),
+		new FbDecFloat(1, -399),
+		(FbDecFloat)(0.1 + 0.2),
+		(FbDecFloat)decimal.MaxValue,
+	};
+
 	[TestCaseSource(nameof(TestValues))]
 	public async Task ReadsValueCorrectly(FbDecFloat value, string castValue)
 	{
@@ -88,6 +106,22 @@ public async Task PassesValueCorrectly(FbDecFloat value, string dummy)
 		}
 	}
 
+	[TestCaseSource(nameof(UnrepresentableValues))]
+	public async Task PassesUnrepresentableValueThrows(FbDecFloat value)
+	{
+		await using (var cmd = Connection.CreateCommand())
+		{
+			cmd.CommandText = "select cast(@value as decfloat(16)) from rdb$database";
+			cmd.Parameters.AddWithValue("value", value);
+			Assert.ThrowsAsync<OverflowException>(() => cmd.ExecuteScalarAsync());
+		}
+		await using (var cmd = Connection.CreateCommand())
+		{
+			cmd.CommandText = "select cast(1 as decfloat(16)) from rdb$database";
+			Assert.AreEqual((FbDecFloat)1, (FbDecFloat)await cmd.ExecuteScalarAsync(), "connection must remain usable");
+		}
+	}
+
 	[Test]
 	public async Task ReadsValueNullCorrectly()
 	{
@@ -111,6 +145,152 @@ public async Task PassesValueNullCorrectly()
 		}
 	}
 
+	static readonly object[] ClrValues = new[]
+	{
+			new object[] { 2.5m, "25", -1 },
+			new object[] { 1.10m, "110", -2 },
+			new object[] { -100m, "-100", 0 },
+			new object[] { 0.1, "1", -1 },
+			new object[] { -6.6, "-66", -1 },
+			new object[] { 2.5f, "25", -1 },
+			new object[] { 42, "42", 0 },
+			new object[] { -42L, "-42", 0 },
+			new object[] { (short)7, "7", 0 },
+			new object[] { (byte)7, "7", 0 },
+			new object[] { 1234567890123456UL, "1234567890123456", 0 },
+			new object[] { new BigInteger(123456789), "123456789", 0 },
+		};
+
+	[TestCaseSource(nameof(ClrValues))]
+	public async Task PassesClrValueCorrectly(object value, string coefficient, int exponent)
+	{
+		await using (var cmd = Connection.CreateCommand())
+		{
+			cmd.CommandText = "select cast(@value as decfloat(16)) from rdb$database";
+			cmd.Parameters.AddWithValue("value", value);
+			var result = (FbDecFloat)await cmd.ExecuteScalarAsync();
+			Assert.AreEqual(new FbDecFloat(BigInteger.Parse(coefficient, CultureInfo.InvariantCulture), exponent), result);
+		}
+	}
+
+	static readonly object[] UnrepresentableClrValues = new object[]
+	{
+		ulong.MaxValue,
+		decimal.MaxValue,
+		0.1 + 0.2,
+		1.0 / 3.0 * 1e-300,
+	};
+
+	[TestCaseSource(nameof(UnrepresentableClrValues))]
+	public async Task PassesUnrepresentableClrValueThrows(object value)
+	{
+		await using (var cmd = Connection.CreateCommand())
+		{
+			cmd.CommandText = "select cast(@value as decfloat(16)) from rdb$database";
+			cmd.Parameters.AddWithValue("value", value);
+			Assert.ThrowsAsync<OverflowException>(() => cmd.ExecuteScalarAsync());
+		}
+	}
+
+	[TestCase("1.10", "1.10")]
+	[TestCase("-123.456", "-123.456")]
+	[TestCase("1E+20", "100000000000000000000")]
+	[TestCase("0", "0")]
+	[TestCase("0.0000000000009999999999999999", "0.0000000000009999999999999999")]
+	public async Task ReadsAsDecimalExactly(string castValue, string expected)
+	{
+		await using (var cmd = Connection.CreateCommand())
+		{
+			cmd.CommandText = $"select cast('{castValue}' as decfloat(16)) from rdb$database";
+			await using (var reader = await cmd.ExecuteReaderAsync())
+			{
+				await reader.ReadAsync();
+				Assert.AreEqual(expected, reader.GetDecimal(0).ToString(CultureInfo.InvariantCulture));
+				Assert.AreEqual(expected, reader.GetFieldValue<decimal>(0).ToString(CultureInfo.InvariantCulture));
+			}
+		}
+	}
+
+	[TestCase("1E+29")]
+	[TestCase("-1E+29")]
+	[TestCase("1E-29")]
+	[TestCase("nan")]
+	[TestCase("inf")]
+	[TestCase("1E+300")]
+	public async Task ReadsAsDecimalThrowsWhenNotExact(string castValue)
+	{
+		await using (var cmd = Connection.CreateCommand())
+		{
+			cmd.CommandText = $"select cast('{castValue}' as decfloat(16)) from rdb$database";
+			await using (var reader = await cmd.ExecuteReaderAsync())
+			{
+				await reader.ReadAsync();
+				Assert.Throws<OverflowException>(() => reader.GetDecimal(0));
+			}
+		}
+	}
+
+	[TestCase("1.10", 1.1)]
+	[TestCase("-6.6", -6.6)]
+	[TestCase("0.1", 0.1)]
+	[TestCase("nan", double.NaN)]
+	[TestCase("inf", double.PositiveInfinity)]
+	[TestCase("-inf", double.NegativeInfinity)]
+	[TestCase("1E-398", 0d)]
+	[TestCase("1E+300", 1E+300)]
+	public async Task ReadsAsDoubleNearest(string castValue, double expected)
+	{
+		await using (var cmd = Connection.CreateCommand())
+		{
+			cmd.CommandText = $"select cast('{castValue}' as decfloat(16)) from rdb$database";
+			await using (var reader = await cmd.ExecuteReaderAsync())
+			{
+				await reader.ReadAsync();
+				Assert.AreEqual(expected, reader.GetDouble(0));
+				Assert.AreEqual((float)expected, reader.GetFloat(0));
+			}
+		}
+	}
+
+	[TestCase("123", 123)]
+	[TestCase("1E+3", 1000)]
+	[TestCase("2.5", 2)]
+	[TestCase("3.5", 4)]
+	[TestCase("-2.5", -2)]
+	[TestCase("-3.5", -4)]
+	[TestCase("2.51", 3)]
+	[TestCase("1E-300", 0)]
+	public async Task ReadsAsIntegerRoundingToEven(string castValue, long expected)
+	{
+		await using (var cmd = Connection.CreateCommand())
+		{
+			cmd.CommandText = $"select cast('{castValue}' as decfloat(16)) from rdb$database";
+			await using (var reader = await cmd.ExecuteReaderAsync())
+			{
+				await reader.ReadAsync();
+				Assert.AreEqual(expected, reader.GetInt64(0));
+				Assert.AreEqual((int)expected, reader.GetInt32(0));
+				Assert.AreEqual((short)expected, reader.GetInt16(0));
+			}
+		}
+	}
+
+	[TestCase("1E+19")]
+	[TestCase("nan")]
+	[TestCase("-inf")]
+	public async Task ReadsAsIntegerThrowsOnOverflow(string castValue)
+	{
+		await using (var cmd = Connection.CreateCommand())
+		{
+			cmd.CommandText = $"select cast('{castValue}' as decfloat(16)) from rdb$database";
+			await using (var reader = await cmd.ExecuteReaderAsync())
+			{
+				await reader.ReadAsync();
+				Assert.Throws<OverflowException>(() => reader.GetInt64(0));
+			}
+		}
+	}
+
 	[Test]
 	public async Task SelectEmptyResultSet()
 	{
diff --git a/src/FirebirdSql.Data.FirebirdClient.Tests/FbDecFloat34SupportTests.cs b/src/FirebirdSql.Data.FirebirdClient.Tests/FbDecFloat34SupportTests.cs
index b1c2bf39f..5f765d23e 100644
--- a/src/FirebirdSql.Data.FirebirdClient.Tests/FbDecFloat34SupportTests.cs
+++ b/src/FirebirdSql.Data.FirebirdClient.Tests/FbDecFloat34SupportTests.cs
@@ -16,6 +16,7 @@
 //$Authors = Jiri Cincura (jiri@cincura.net)
 
 using System;
+using System.Globalization;
 using System.Numerics;
 using System.Threading.Tasks;
 using FirebirdSql.Data.TestsBase;
@@ -63,8 +64,25 @@ public override async Task SetUp()
 			new object[] { new FbDecFloat(-10, 34), "-100000000000000000000000000000000000" },
 			new object[] { new FbDecFloat(BigInteger.Parse("123000000001"), -10), "123.000000001E-1" },
 			new object[] { new FbDecFloat(BigInteger.Parse("-123000000001"), -10), "-123.000000001E-1" },
+			new object[] { new FbDecFloat(1, 6144), "1E6144" },
+			new object[] { new FbDecFloat(BigInteger.Parse("12345678901234567890123456789012340"), 0), "12345678901234567890123456789012340" },
+			new object[] { new FbDecFloat(1000, -6179), "1E-6176" },
+			new object[] { (FbDecFloat)2.0, "2" },
+			new object[] { (FbDecFloat)1e-20, "1E-20" },
+			new object[] { (FbDecFloat)2.5f, "2.5" },
+			new object[] { (FbDecFloat)(0.1 + 0.2), "0.30000000000000004" },
+			new object[] { (FbDecFloat)100m, "100" },
+			new object[] { (FbDecFloat)1.10m, "1.10" },
+			new object[] { (FbDecFloat)decimal.MaxValue, "79228162514264337593543950335" },
 		};
 
+	static readonly object[] UnrepresentableValues = new object[]
+	{
+		new FbDecFloat(BigInteger.Parse("12345678901234567890123456789012345"), 0),
+		new FbDecFloat(1, 6145),
+		new FbDecFloat(1, -6177),
+	};
+
 	[TestCaseSource(nameof(TestValues))]
 	public async Task ReadsValueCorrectly(FbDecFloat value, string castValue)
 	{
@@ -88,6 +106,22 @@ public async Task PassesValueCorrectly(FbDecFloat value, string dummy)
 		}
 	}
 
+	[TestCaseSource(nameof(UnrepresentableValues))]
+	public async Task PassesUnrepresentableValueThrows(FbDecFloat value)
+	{
+		await using (var cmd = Connection.CreateCommand())
+		{
+			cmd.CommandText = "select cast(@value as decfloat(34)) from rdb$database";
+			cmd.Parameters.AddWithValue("value", value);
+			Assert.ThrowsAsync<OverflowException>(() => cmd.ExecuteScalarAsync());
+		}
+		await using (var cmd = Connection.CreateCommand())
+		{
+			cmd.CommandText = "select cast(1 as decfloat(34)) from rdb$database";
+			Assert.AreEqual((FbDecFloat)1, (FbDecFloat)await cmd.ExecuteScalarAsync(), "connection must remain usable");
+		}
+	}
+
 	[Test]
 	public async Task ReadsValueNullCorrectly()
 	{
@@ -111,6 +145,137 @@ public async Task PassesValueNullCorrectly()
 		}
 	}
 
+	static readonly object[] ClrValues = new[]
+	{
+			new object[] { 2.5m, "25", -1 },
+			new object[] { 1.10m, "110", -2 },
+			new object[] { -100m, "-100", 0 },
+			new object[] { 0.1, "1", -1 },
+			new object[] { -6.6, "-66", -1 },
+			new object[] { 2.5f, "25", -1 },
+			new object[] { 42, "42", 0 },
+			new object[] { -42L, "-42", 0 },
+			new object[] { (short)7, "7", 0 },
+			new object[] { (byte)7, "7", 0 },
+			new object[] { ulong.MaxValue, "18446744073709551615", 0 },
+			new object[] { new BigInteger(123456789), "123456789", 0 },
+		};
+
+	[TestCaseSource(nameof(ClrValues))]
+	public async Task PassesClrValueCorrectly(object value, string coefficient, int exponent)
+	{
+		await using (var cmd = Connection.CreateCommand())
+		{
+			cmd.CommandText = "select cast(@value as decfloat(34)) from rdb$database";
+			cmd.Parameters.AddWithValue("value", value);
+			var result = (FbDecFloat)await cmd.ExecuteScalarAsync();
+			Assert.AreEqual(new FbDecFloat(BigInteger.Parse(coefficient, CultureInfo.InvariantCulture), exponent), result);
+		}
+	}
+
+	[TestCase("1.10", "1.10")]
+	[TestCase("-123.456", "-123.456")]
+	[TestCase("1E+20", "100000000000000000000")]
+	[TestCase("0", "0")]
+	[TestCase("0.0000000000009999999999999999", "0.0000000000009999999999999999")]
+	[TestCase("1234567890123456789012345678.9", "1234567890123456789012345678.9")]
+	[TestCase("7.9228162514264337593543950335", "7.9228162514264337593543950335")]
+	public async Task ReadsAsDecimalExactly(string castValue, string expected)
+	{
+		await using (var cmd = Connection.CreateCommand())
+		{
+			cmd.CommandText = $"select cast('{castValue}' as decfloat(34)) from rdb$database";
+			await using (var reader = await cmd.ExecuteReaderAsync())
+			{
+				await reader.ReadAsync();
+				Assert.AreEqual(expected, reader.GetDecimal(0).ToString(CultureInfo.InvariantCulture));
+				Assert.AreEqual(expected, reader.GetFieldValue<decimal>(0).ToString(CultureInfo.InvariantCulture));
+			}
+		}
+	}
+
+	[TestCase("1E+29")]
+	[TestCase("-1E+29")]
+	[TestCase("1E-29")]
+	[TestCase("nan")]
+	[TestCase("inf")]
+	[TestCase("1.0000000000000000000000000000001")]
+	[TestCase("79228162514264337593543950336")]
+	public async Task ReadsAsDecimalThrowsWhenNotExact(string castValue)
+	{
+		await using (var cmd = Connection.CreateCommand())
+		{
+			cmd.CommandText = $"select cast('{castValue}' as decfloat(34)) from rdb$database";
+			await using (var reader = await cmd.ExecuteReaderAsync())
+			{
+				await reader.ReadAsync();
+				Assert.Throws<OverflowException>(() => reader.GetDecimal(0));
+			}
+		}
+	}
+
+	[TestCase("1.10", 1.1)]
+	[TestCase("-6.6", -6.6)]
+	[TestCase("0.1", 0.1)]
+	[TestCase("nan", double.NaN)]
+	[TestCase("inf", double.PositiveInfinity)]
+	[TestCase("-inf", double.NegativeInfinity)]
+	[TestCase("1E-6000", 0d)]
+	[TestCase("1E+6000", double.PositiveInfinity)]
+	[TestCase("0.30000000000000004", 0.30000000000000004)]
+	public async Task ReadsAsDoubleNearest(string castValue, double expected)
+	{
+		await using (var cmd = Connection.CreateCommand())
+		{
+			cmd.CommandText = $"select cast('{castValue}' as decfloat(34)) from rdb$database";
+			await using (var reader = await cmd.ExecuteReaderAsync())
+			{
+				await reader.ReadAsync();
+				Assert.AreEqual(expected, reader.GetDouble(0));
+				Assert.AreEqual((float)expected, reader.GetFloat(0));
+			}
+		}
+	}
+
+	[TestCase("123", 123)]
+	[TestCase("1E+3", 1000)]
+	[TestCase("2.5", 2)]
+	[TestCase("3.5", 4)]
+	[TestCase("-2.5", -2)]
+	[TestCase("-3.5", -4)]
+	[TestCase("2.51", 3)]
+	[TestCase("1E-300", 0)]
+	public async Task ReadsAsIntegerRoundingToEven(string castValue, long expected)
+	{
+		await using (var cmd = Connection.CreateCommand())
+		{
+			cmd.CommandText = $"select cast('{castValue}' as decfloat(34)) from rdb$database";
+			await using (var reader = await cmd.ExecuteReaderAsync())
+			{
+				await reader.ReadAsync();
+				Assert.AreEqual(expected, reader.GetInt64(0));
+				Assert.AreEqual((int)expected, reader.GetInt32(0));
+				Assert.AreEqual((short)expected, reader.GetInt16(0));
+			}
+		}
+	}
+
+	[TestCase("1E+19")]
+	[TestCase("nan")]
+	[TestCase("-inf")]
+	public async Task ReadsAsIntegerThrowsOnOverflow(string castValue)
+	{
+		await using (var cmd = Connection.CreateCommand())
+		{
+			cmd.CommandText = $"select cast('{castValue}' as decfloat(34)) from rdb$database";
+			await using (var reader = await cmd.ExecuteReaderAsync())
+			{
+				await reader.ReadAsync();
+				Assert.Throws<OverflowException>(() => reader.GetInt64(0));
+			}
+		}
+	}
+
 	[Test]
 	public async Task SelectEmptyResultSet()
 	{
diff --git a/src/FirebirdSql.Data.FirebirdClient.Tests/FbDecFloatTypeTests.cs b/src/FirebirdSql.Data.FirebirdClient.Tests/FbDecFloatTypeTests.cs
index 4df15b2d5..e44e697ea 100644
--- a/src/FirebirdSql.Data.FirebirdClient.Tests/FbDecFloatTypeTests.cs
+++ b/src/FirebirdSql.Data.FirebirdClient.Tests/FbDecFloatTypeTests.cs
@@ -15,6 +15,8 @@
 
 //$Authors = Jiri Cincura (jiri@cincura.net)
 
+using System;
+using System.Globalization;
 using System.Numerics;
 using FirebirdSql.Data.TestsBase;
 using FirebirdSql.Data.Types;
@@ -72,4 +74,190 @@ public void EqualityFalse(FbDecFloat expected, FbDecFloat actual)
 	{
 		Assert.AreNotEqual(expected, actual);
 	}
+
+	static readonly object[] DecimalConversionSource = new object[]
+	{
+			new object[] { 0m, "0", 0 },
+			new object[] { 1m, "1", 0 },
+			new object[] { 100m, "100", 0 },
+			new object[] { -5m, "-5", 0 },
+			new object[] { 1.5m, "15", -1 },
+			new object[] { 1.10m, "110", -2 },
+			new object[] { -0.001m, "-1", -3 },
+			new object[] { decimal.MaxValue, "79228162514264337593543950335", 0 },
+			new object[] { decimal.MinValue, "-79228162514264337593543950335", 0 },
+			new object[] { 0.0000000000000000000000000001m, "1", -28 },
+			new object[] { -7.9228162514264337593543950335m, "-79228162514264337593543950335", -28 },
+	};
+	[TestCaseSource(nameof(DecimalConversionSource))]
+	public void ConvertsDecimalExactly(decimal value, string coefficient, int exponent)
+	{
+		var result = (FbDecFloat)value;
+		Assert.AreEqual(BigInteger.Parse(coefficient), result.Coefficient);
+		Assert.AreEqual(exponent, result.Exponent);
+	}
+
+	static readonly object[] DoubleConversionSource = new object[]
+	{
+			new object[] { 0d, "0", 0 },
+			new object[] { 2d, "2", 0 },
+			new object[] { 100d, "100", 0 },
+			new object[] { 0.1, "1", -1 },
+			new object[] { -6.6, "-66", -1 },
+			new object[] { 1e-20, "1", -20 },
+			new object[] { 1e300, "1", 300 },
+			new object[] { 0.1 + 0.2, "30000000000000004", -17 },
+			new object[] { 123456789.123456789, "12345678912345679", -8 },
+			new object[] { double.MaxValue, "17976931348623157", 292 },
+			new object[] { double.MinValue, "-17976931348623157", 292 },
+			new object[] { double.Epsilon, "5", -324 },
+	};
+	[TestCaseSource(nameof(DoubleConversionSource))]
+	public void ConvertsDoubleToShortestRoundTripValue(double value, string coefficient, int exponent)
+	{
+		var result = (FbDecFloat)value;
+		Assert.AreEqual(BigInteger.Parse(coefficient), result.Coefficient);
+		Assert.AreEqual(exponent, result.Exponent);
+	}
+
+	static readonly object[] SingleConversionSource = new object[]
+	{
+			new object[] { 2f, "2", 0 },
+			new object[] { 0.1f, "1", -1 },
+			new object[] { -6.6f, "-66", -1 },
+			new object[] { 1e-20f, "1", -20 },
+			new object[] { float.MaxValue, "34028235", 31 },
+			new object[] { float.Epsilon, "1", -45 },
+	};
+	[TestCaseSource(nameof(SingleConversionSource))]
+	public void ConvertsSingleToShortestRoundTripValue(float value, string coefficient, int exponent)
+	{
+		var result = (FbDecFloat)value;
+		Assert.AreEqual(BigInteger.Parse(coefficient), result.Coefficient);
+		Assert.AreEqual(exponent, result.Exponent);
+	}
+
+	[Test]
+	public void ConvertsNegativeZero()
+	{
+		Assert.AreEqual(FbDecFloat.NegativeZero, (FbDecFloat)(-0d));
+		Assert.AreEqual(FbDecFloat.NegativeZero, (FbDecFloat)(-0f));
+		Assert.AreEqual(FbDecFloat.NegativeZero, (FbDecFloat)decimal.Negate(0m));
+		Assert.AreNotEqual(FbDecFloat.NegativeZero, (FbDecFloat)0d);
+		Assert.AreNotEqual(FbDecFloat.NegativeZero, (FbDecFloat)0m);
+	}
+
+	[Test]
+	public void ConvertsSpecialValues()
+	{
+		Assert.AreEqual(FbDecFloat.PositiveNaN, (FbDecFloat)double.NaN);
+		Assert.AreEqual(FbDecFloat.PositiveInfinity, (FbDecFloat)double.PositiveInfinity);
+		Assert.AreEqual(FbDecFloat.NegativeInfinity, (FbDecFloat)double.NegativeInfinity);
+		Assert.AreEqual(FbDecFloat.PositiveNaN, (FbDecFloat)float.NaN);
+		Assert.AreEqual(FbDecFloat.PositiveInfinity, (FbDecFloat)float.PositiveInfinity);
+		Assert.AreEqual(FbDecFloat.NegativeInfinity, (FbDecFloat)float.NegativeInfinity);
+	}
+
+	[Test]
+	public void DoubleAndSingleConversionsRoundTrip()
+	{
+		var random = new Random(20261107);
+		var negativeDoubles = 0;
+		var negativeSingles = 0;
+		for (var i = 0; i < 10_000; i++)
+		{
+			// random bit patterns, so all exponents and both signs are covered
+			var d = BitConverter.Int64BitsToDouble(random.NextInt64(long.MinValue, long.MaxValue));
+			if (double.IsFinite(d))
+			{
+				var result = (FbDecFloat)d;
+				Assert.AreEqual(d, double.Parse(result.ToString(), CultureInfo.InvariantCulture), $"{d:R} -> {result}");
+				negativeDoubles += d < 0 ? 1 : 0;
+			}
+			var f = BitConverter.Int32BitsToSingle(random.Next(int.MinValue, int.MaxValue));
+			if (float.IsFinite(f))
+			{
+				var result = (FbDecFloat)f;
+				Assert.AreEqual(f, float.Parse(result.ToString(), CultureInfo.InvariantCulture), $"{f:R} -> {result}");
+				negativeSingles += f < 0 ? 1 : 0;
+			}
+		}
+		Assert.Greater(negativeDoubles, 1000);
+		Assert.Greater(negativeSingles, 1000);
+	}
+	static readonly object[] ToDecimalSource = new object[]
+	{
+			new object[] { new FbDecFloat(110, -2), "1.10" },
+			new object[] { new FbDecFloat(-5, 0), "-5" },
+			new object[] { new FbDecFloat(1, 28), "10000000000000000000000000000" },
+			new object[] { new FbDecFloat(BigInteger.Parse("79228162514264337593543950335"), 0), "79228162514264337593543950335" },
+			new object[] { new FbDecFloat(BigInteger.Parse("792281625142643375935439503350"), -1), "79228162514264337593543950335" },
+			new object[] { new FbDecFloat(1, -28), "0.0000000000000000000000000001" },
+			new object[] { new FbDecFloat(1000, -31), "0.0000000000000000000000000001" },
+			new object[] { new FbDecFloat(0, -40), "0.0000000000000000000000000000" },
+			new object[] { new FbDecFloat(0, 40), "0" },
+	};
+	[TestCaseSource(nameof(ToDecimalSource))]
+	public void ConvertsToDecimalExactly(FbDecFloat value, string expected)
+	{
+		Assert.AreEqual(expected, ((decimal)value).ToString(CultureInfo.InvariantCulture));
+	}
+
+	static readonly object[] ToDecimalThrowsSource = new object[]
+	{
+			new FbDecFloat(1, 29),
+			new FbDecFloat(BigInteger.Parse("79228162514264337593543950336"), 0),
+			new FbDecFloat(1, -29),
+			new FbDecFloat(BigInteger.Parse("10000000000000000000000000000001"), -31),
+			new FbDecFloat(1, int.MaxValue),
+			new FbDecFloat(1, int.MinValue),
+			FbDecFloat.PositiveNaN,
+			FbDecFloat.PositiveSignalingNaN,
+			FbDecFloat.NegativeInfinity,
+	};
+	[TestCaseSource(nameof(ToDecimalThrowsSource))]
+	public void ConvertsToDecimalThrowsWhenNotExact(FbDecFloat value)
+	{
+		Assert.Throws<OverflowException>(() => _ = (decimal)value);
+	}
+
+	static readonly object[] ToDoubleSource = new object[]
+	{
+			new object[] { new FbDecFloat(66, -1), 6.6 },
+			new object[] { new FbDecFloat(BigInteger.Parse("30000000000000004"), -17), 0.1 + 0.2 },
+			new object[] { new FbDecFloat(1, 400), double.PositiveInfinity },
+			new object[] { new FbDecFloat(-1, 400), double.NegativeInfinity },
+			new object[] { new FbDecFloat(1, -400), 0d },
+			new object[] { FbDecFloat.PositiveInfinity, double.PositiveInfinity },
+			new object[] { FbDecFloat.NegativeInfinity, double.NegativeInfinity },
+			new object[] { FbDecFloat.PositiveNaN, double.NaN },
+			new object[] { FbDecFloat.NegativeSignalingNaN, double.NaN },
+	};
+	[TestCaseSource(nameof(ToDoubleSource))]
+	public void ConvertsToNearestDouble(FbDecFloat value, double expected)
+	{
+		Assert.AreEqual(expected, (double)value);
+		Assert.AreEqual((float)expected, (float)value);
+	}
+
+	[Test]
+	public void ConvertsNegativeZeroToFloatingPoint()
+	{
+		Assert.IsTrue(double.IsNegative((double)FbDecFloat.NegativeZero));
+		Assert.IsTrue(float.IsNegative((float)FbDecFloat.NegativeZero));
+	}
+
+	[TestCase("2", 1, 20)]
+	[TestCase("25", -1, 2)]
+	[TestCase("35", -1, 4)]
+	[TestCase("-25", -1, -2)]
+	[TestCase("251", -2, 3)]
+	[TestCase("5", -1, 0)]
+	[TestCase("15", -1, 2)]
+	[TestCase("1", int.MinValue, 0)]
+	public void RoundsToIntegerToEven(string coefficient, int exponent, long expected)
+	{
+		var value = new FbDecFloat(BigInteger.Parse(coefficient), exponent);
+		Assert.AreEqual(new BigInteger(expected), value.ToIntegerRoundingToEven());
+	}
 }
diff --git a/src/FirebirdSql.Data.FirebirdClient/Common/DbValue.cs b/src/FirebirdSql.Data.FirebirdClient/Common/DbValue.cs
index 44b79a0f1..70e1827c0 100644
--- a/src/FirebirdSql.Data.FirebirdClient/Common/DbValue.cs
+++ b/src/FirebirdSql.Data.FirebirdClient/Common/DbValue.cs
@@ -189,6 +189,7 @@ public byte GetByte()
 		return _value switch
 		{
 			BigInteger bi => (byte)bi,
+			FbDecFloat df => (byte)df.ToIntegerRoundingToEven(),
 			_ => Convert.ToByte(_value, CultureInfo.InvariantCulture),
 		};
 	}
@@ -198,6 +199,7 @@ public short GetInt16()
 		return _value switch
 		{
 			BigInteger bi => (short)bi,
+			FbDecFloat df => (short)df.ToIntegerRoundingToEven(),
 			_ => Convert.ToInt16(_value, CultureInfo.InvariantCulture),
 		};
 	}
@@ -207,6 +209,7 @@ public int GetInt32()
 		return _value switch
 		{
 			BigInteger bi => (int)bi,
+			FbDecFloat df => (int)df.ToIntegerRoundingToEven(),
 			_ => Convert.ToInt32(_value, CultureInfo.InvariantCulture),
 		};
 	}
@@ -216,18 +219,27 @@ public long GetInt64()
 		return _value switch
 		{
 			BigInteger bi => (long)bi,
+			FbDecFloat df => (long)df.ToIntegerRoundingToEven(),
 			_ => Convert.ToInt64(_value, CultureInfo.InvariantCulture),
 		};
 	}
 
 	public decimal GetDecimal()
 	{
-		return Convert.ToDecimal(_value, CultureInfo.InvariantCulture);
+		return _value switch
+		{
+			FbDecFloat df => (decimal)df,
+			_ => Convert.ToDecimal(_value, CultureInfo.InvariantCulture),
+		};
 	}
 
 	public float GetFloat()
 	{
-		return Convert.ToSingle(_value, CultureInfo.InvariantCulture);
+		return _value switch
+		{
+			FbDecFloat df => (float)df,
+			_ => Convert.ToSingle(_value, CultureInfo.InvariantCulture),
+		};
 	}
 
 	public Guid GetGuid()
@@ -242,7 +254,11 @@ public Guid GetGuid()
 
 	public double GetDouble()
 	{
-		return Convert.ToDouble(_value, CultureInfo.InvariantCulture);
+		return _value switch
+		{
+			FbDecFloat df => (double)df,
+			_ => Convert.ToDouble(_value, CultureInfo.InvariantCulture),
+		};
 	}
 
 	public DateTime GetDateTime()
@@ -262,7 +278,23 @@ public TimeSpan GetTimeSpan()
 
 	public FbDecFloat GetDecFloat()
 	{
-		return (FbDecFloat)_value;
+		return _value switch
+		{
+			FbDecFloat df => df,
+			decimal d => (FbDecFloat)d,
+			double d => (FbDecFloat)d,
+			float f => (FbDecFloat)f,
+			byte b => b,
+			sbyte sb => sb,
+			short s => s,
+			ushort us => us,
+			int i => i,
+			uint ui => ui,
+			long l => l,
+			ulong ul => ul,
+			BigInteger bi => new FbDecFloat(bi),
+			_ => (FbDecFloat)_value,
+		};
 	}
 
 	public BigInteger GetInt128()
diff --git a/src/FirebirdSql.Data.FirebirdClient/Common/DecimalCodec.cs b/src/FirebirdSql.Data.FirebirdClient/Common/DecimalCodec.cs
index 5ff63ddee..8a7f8f9c6 100644
--- a/src/FirebirdSql.Data.FirebirdClient/Common/DecimalCodec.cs
+++ b/src/FirebirdSql.Data.FirebirdClient/Common/DecimalCodec.cs
@@ -17,6 +17,7 @@
 
 using System;
 using System.Diagnostics;
+using System.Numerics;
 using FirebirdSql.Data.Types;
 
 namespace FirebirdSql.Data.Common;
@@ -41,6 +42,9 @@ public DecimalFormat(int formatBitLength, int coefficientDigits)
 			ELimit = 3 * (1 << ExponentContinuationBits) - 1;
 			EMin = -ELimit / 2;
 			ExponentBias = -EMin + CoefficientDigits - 1;
+			MaxCoefficient = BigInteger.Pow(10, CoefficientDigits) - 1;
+			MinExponent = UnbiasedExponent(0);
+			MaxExponent = UnbiasedExponent(ELimit);
 		}
 
 		public int FormatBitLength { get; }
@@ -51,6 +55,10 @@ public DecimalFormat(int formatBitLength, int coefficientDigits)
 		public int ELimit { get; }
 		public int EMin { get; }
 		public int ExponentBias { get; }
+		public BigInteger MaxCoefficient { get; }
+		// Range of the exponent applied to the integral coefficient (value = coefficient * 10^exponent).
+		public int MinExponent { get; }
+		public int MaxExponent { get; }
 
 		public void ValidateByteLength(byte[] decBytes)
 		{
@@ -171,8 +179,8 @@ public byte[] EncodeDecimal(FbDecFloat @decimal)
 
 	void EncodeFinite(FbDecFloat @decimal, byte[] decBytes)
 	{
-		var biasedExponent = _decimalFormat.BiasedExponent(@decimal.Exponent);
-		var coefficient = @decimal.Coefficient;
+		var (coefficient, exponent) = FitToFormat(@decimal);
+		var biasedExponent = _decimalFormat.BiasedExponent(exponent);
 		var mostSignificantDigit = _coefficientCoder.EncodeValue(coefficient, decBytes);
 		var expMSB = biasedExponent >>> _decimalFormat.ExponentContinuationBits;
 		var expTwoBitCont = (biasedExponent >>> _decimalFormat.ExponentContinuationBits - 2) & 0b011;
@@ -192,6 +200,52 @@ void EncodeFinite(FbDecFloat @decimal, byte[] decBytes)
 		EncodeExponentContinuation(decBytes, biasedExponent, _decimalFormat.ExponentContinuationBits - 2);
 	}
 
+	// Brings the coefficient and exponent into the ranges of the format without changing the numeric value
+	// (removing trailing zeros of the coefficient, or moving the exponent into the coefficient).
+	// Throws when that is impossible, i.e. when the value would have to be rounded, or overflows or underflows the format.
+	(BigInteger coefficient, int exponent) FitToFormat(FbDecFloat @decimal)
+	{
+		var coefficient = BigInteger.Abs(@decimal.Coefficient);
+		long exponent = @decimal.Exponent;
+		if (coefficient.IsZero)
+		{
+			return (coefficient, (int)Math.Clamp(exponent, _decimalFormat.MinExponent, _decimalFormat.MaxExponent));
+		}
+		while (coefficient > _decimalFormat.MaxCoefficient)
+		{
+			coefficient = BigInteger.DivRem(coefficient, 10, out var remainder);
+			if (!remainder.IsZero)
+			{
+				throw CannotRepresent(@decimal, $"more than {_decimalFormat.CoefficientDigits} significant digits");
+			}
+			exponent++;
+		}
+		while (exponent > _decimalFormat.MaxExponent)
+		{
+			coefficient *= 10;
+			if (coefficient > _decimalFormat.MaxCoefficient)
+			{
+				throw CannotRepresent(@decimal, "exponent overflow");
+			}
+			exponent--;
+		}
+		while (exponent < _decimalFormat.MinExponent)
+		{
+			coefficient = BigInteger.DivRem(coefficient, 10, out var remainder);
+			if (!remainder.IsZero)
+			{
+				throw CannotRepresent(@decimal, "exponent underflow");
+			}
+			exponent++;
+		}
+		return (coefficient, (int)exponent);
+	}
+
+	OverflowException CannotRepresent(FbDecFloat @decimal, string reason)
+	{
+		return new OverflowException($"Value {@decimal} cannot be represented exactly as DECFLOAT({_decimalFormat.CoefficientDigits}): {reason}.");
+	}
+
 	static void EncodeExponentContinuation(byte[] decBytes, int expAndBias, int expBitsRemaining)
 	{
 		var expByteIndex = 1;
diff --git a/src/FirebirdSql.Data.FirebirdClient/Types/FbDecFloat.cs b/src/FirebirdSql.Data.FirebirdClient/Types/FbDecFloat.cs
index 29c37c4ee..c901fe992 100644
--- a/src/FirebirdSql.Data.FirebirdClient/Types/FbDecFloat.cs
+++ b/src/FirebirdSql.Data.FirebirdClient/Types/FbDecFloat.cs
@@ -64,16 +64,120 @@ public FbDecFloat(BigInteger coefficient, int exponent = 0)
 		float.NaN => PositiveNaN,
 		float.PositiveInfinity => PositiveInfinity,
 		float.NegativeInfinity => NegativeInfinity,
-		_ => ParseNumber(value, "0.#######"),
+		// shortest representation that round-trips to the same float
+		_ => ParseRoundTrip(value.ToString("R", CultureInfo.InvariantCulture)),
 	};
 	public static explicit operator FbDecFloat(double value) => value switch
 	{
 		double.NaN => PositiveNaN,
 		double.PositiveInfinity => PositiveInfinity,
 		double.NegativeInfinity => NegativeInfinity,
-		_ => ParseNumber(value, "0.###############"),
+		// shortest representation that round-trips to the same double
+		_ => ParseRoundTrip(value.ToString("R", CultureInfo.InvariantCulture)),
 	};
-	public static explicit operator FbDecFloat(decimal value) => ParseNumber(value, "0.############################");
+	public static explicit operator FbDecFloat(decimal value)
+	{
+		// exact: the decimal's 96-bit integer and scale are the coefficient and (negated) exponent
+		Span<int> bits = stackalloc int[4];
+		decimal.GetBits(value, bits);
+		BigInteger coefficient = ((UInt128)(uint)bits[2] << 64) | ((UInt128)(uint)bits[1] << 32) | (uint)bits[0];
+		var negative = bits[3] < 0;
+		var scale = (bits[3] >> 16) & 0xFF;
+		return new FbDecFloat(DecimalType.Finite, negative, negative ? -coefficient : coefficient, -scale);
+	}
+
+	// Exact (the scale is kept when possible, e.g. 110E-2 -> 1.10m).
+	// Throws OverflowException when the value cannot be represented exactly as decimal, including NaN and infinities.
+	public static explicit operator decimal(FbDecFloat value)
+	{
+		if (value.Type != DecimalType.Finite)
+		{
+			throw value.CannotRepresent(nameof(Decimal));
+		}
+		var coefficient = BigInteger.Abs(value.Coefficient);
+		var exponent = value.Exponent;
+		if (exponent > 0)
+		{
+			if (!coefficient.IsZero)
+			{
+				if (exponent > 28)
+				{
+					throw value.CannotRepresent(nameof(Decimal));
+				}
+				coefficient *= BigInteger.Pow(10, exponent);
+			}
+			exponent = 0;
+		}
+		// only trailing zeros can be dropped
+		while (exponent < 0 && (exponent < -28 || coefficient > MaxDecimalCoefficient))
+		{
+			var quotient = BigInteger.DivRem(coefficient, 10, out var remainder);
+			if (!remainder.IsZero)
+			{
+				break;
+			}
+			coefficient = quotient;
+			exponent++;
+		}
+		if (exponent < -28 || coefficient > MaxDecimalCoefficient)
+		{
+			throw value.CannotRepresent(nameof(Decimal));
+		}
+		var bits = (UInt128)coefficient;
+		return new decimal((int)(uint)bits, (int)(uint)(bits >> 32), (int)(uint)(bits >> 64), value.Negative, (byte)-exponent);
+	}
+	// Nearest double (overflows to infinity, underflows to zero); NaN and infinities are mapped.
+	public static explicit operator double(FbDecFloat value) => value.Type switch
+	{
+		DecimalType.Infinity => value.Negative ? double.NegativeInfinity : double.PositiveInfinity,
+		DecimalType.NaN or DecimalType.SignalingNaN => double.NaN,
+		_ => value.Negative && value.Coefficient.IsZero ? -0d : double.Parse(value.ToInvariantScientificString(), NumberStyles.Float, CultureInfo.InvariantCulture),
+	};
+	// Nearest float (overflows to infinity, underflows to zero); NaN and infinities are mapped.
+	public static explicit operator float(FbDecFloat value) => value.Type switch
+	{
+		DecimalType.Infinity => value.Negative ? float.NegativeInfinity : float.PositiveInfinity,
+		DecimalType.NaN or DecimalType.SignalingNaN => float.NaN,
+		_ => value.Negative && value.Coefficient.IsZero ? -0f : float.Parse(value.ToInvariantScientificString(), NumberStyles.Float, CultureInfo.InvariantCulture),
+	};
+
+	static readonly BigInteger MaxDecimalCoefficient = (BigInteger)decimal.MaxValue;
+
+	string ToInvariantScientificString() => $"{Coefficient.ToString(CultureInfo.InvariantCulture)}E{Exponent.ToString(CultureInfo.InvariantCulture)}";
+
+	OverflowException CannotRepresent(string type) => new OverflowException($"Value {this} cannot be represented exactly as {type}.");
+
+	// Nearest integer, ties to even (as Convert.ToInt64(decimal) does).
+	// Throws OverflowException for NaN, infinities and values far beyond the 64-bit range.
+	internal BigInteger ToIntegerRoundingToEven()
+	{
+		if (Type != DecimalType.Finite)
+		{
+			throw CannotRepresent(nameof(BigInteger));
+		}
+		if (Exponent >= 0)
+		{
+			if (Exponent > 40 && !Coefficient.IsZero)
+			{
+				throw CannotRepresent(nameof(BigInteger));
+			}
+			return Coefficient * BigInteger.Pow(10, Exponent);
+		}
+		var digitsToDrop = -(long)Exponent;
+		if (digitsToDrop > BigInteger.Abs(Coefficient).GetBitLength())
+		{
+			// |value| < 0.5
+			return BigInteger.Zero;
+		}
+		var divisor = BigInteger.Pow(10, (int)digitsToDrop);
+		var quotient = BigInteger.DivRem(Coefficient, divisor, out var remainder);
+		var twice = BigInteger.Abs(remainder) * 2;
+		if (twice > divisor || (twice == divisor && !quotient.IsEven))
+		{
+			quotient += Coefficient.Sign;
+		}
+		return quotient;
+	}
 
 	public override string ToString()
 	{
@@ -155,10 +259,23 @@ public bool Equals(FbDecFloat other)
 		return !lhs.Equals(rhs);
 	}
 
-	static FbDecFloat ParseNumber(IFormattable formattable, string format)
+	// Parses the invariant "R" format of float/double, e.g. "2", "-0", "6.6", "1E-20", "1.7976931348623157E+308".
+	static FbDecFloat ParseRoundTrip(string s)
 	{
-		var s = formattable.ToString(format, CultureInfo.InvariantCulture);
-		var pos = s.IndexOf('.');
-		return new FbDecFloat(BigInteger.Parse(s.Remove(pos, 1), CultureInfo.InvariantCulture), -(s.Length - pos - 1));
+		var exponent = 0;
+		var exponentPos = s.IndexOf('E');
+		if (exponentPos >= 0)
+		{
+			exponent = int.Parse(s.AsSpan(exponentPos + 1), NumberStyles.AllowLeadingSign, CultureInfo.InvariantCulture);
+			s = s.Substring(0, exponentPos);
+		}
+		var pointPos = s.IndexOf('.');
+		if (pointPos >= 0)
+		{
+			exponent -= s.Length - pointPos - 1;
+			s = s.Remove(pointPos, 1);
+		}
+		var coefficient = BigInteger.Parse(s, NumberStyles.AllowLeadingSign, CultureInfo.InvariantCulture);
+		return new FbDecFloat(DecimalType.Finite, s[0] == '-', coefficient, exponent);
 	}
 }