Convert A Binary Float To FLOAT Datatype

I can't take full credit for this. I want to share this with Jeff Moden who did the important research for this calculation here.

All I did was just adapting some old code according to the mantissa finding Jeff made and optimized it a little


Some test codeDECLARE@SomeNumber FLOAT,
@BinFloat BINARY(8)

SELECT@SomeNumber = -185.6125,
@BinFloat = CAST(@SomeNumber AS BINARY(8))

SELECT@SomeNumber AS [Original],
CAST(@SomeNumber AS BINARY(8)) AS [Binary],
dbo.fnBinaryFloat2Float(CAST(@SomeNumber AS BINARY(8))) AS [Converted],
@SomeNumber - dbo.fnBinaryFloat2Float(CAST(@SomeNumber AS BINARY(8))) AS [Error]

And here is the code for the function.CREATE FUNCTION dbo.fnBinaryFloat2Float
(
@BinaryFloat BINARY(8)
)
RETURNS FLOAT
AS
BEGIN
DECLARE@Part TINYINT,
@PartValue TINYINT,
@Mask TINYINT,
@Mantissa FLOAT,
@Exponent SMALLINT,
@Bit TINYINT,
@Ln2 FLOAT,
@BigValue BIGINT

SELECT@Part = 1,
@Mantissa = 1,
@Bit = 1,
@Ln2 = LOG(2),
@BigValue = CAST(@BinaryFloat AS BIGINT),
@Exponent = (@BigValue & 0x7ff0000000000000) / EXP(52 * @Ln2)

WHILE @Part <= 8
BEGIN
SELECT@Part = @Part + 1,
@PartValue = CAST(SUBSTRING(@BinaryFloat, @Part, 1) AS TINYINT),
@Mask =CASE WHEN @Part = 2 THEN 8 ELSE 128 END

WHILE @Mask > 0
BEGIN
IF @PartValue & @Mask > 0
SET @Mantissa = @Mantissa + EXP(-@Bit * @Ln2)

SELECT@Bit = @Bit + 1,
@Mask = @Mask / 2
END
END

RETURNSIGN(@BigValue) * @Mantissa * POWER(CAST(2 AS FLOAT), @Exponent - 1023)
END
Thanks again Jeff!


Peter Larsson
Helsingborg, Sweden