Inspired/challenged by Hans Lindgren's stored procedures of these same names
posted on SQLServerCentral, I created these. Note that they produce strange
results on non-hexadecimal strings, and may have issues with byte-ordering
in some architectures (but Itanium is little-endian like x86 and x64,
right?).
How do they work? well, the distance between one after '9' (':') and 'A' is
7 in ASCII. Also, if I subtract 48 from an upper-cased hex-digit, digit & 16
will always be equal to 16. So I can mask that bit out, shift it down 4 bits
(/16), multiply by 7, subtract from the original value, and come up with a
value from 0 to 15. This can be done on all 8 digits in parallel, as you can
see below.
I use CAST(CAST('1234ABCD' AS BINARY(8))AS BIGINT) to put the hex value
1234ABCD into a number I can manipulate, then subtract the value '00000000'
(CAST(0x3030303030303030 AS BIGINT)), then mask out the hex overflow bits,
shift right, multiply by 7, subtract to make the values 0x010203040A0B0C0D,
then I shift the bits into the proper places and add.
It's probably easier in assembly language than SQL, but oh well.
It's only about 20% faster than Hans's series of CHARINDEX calls.
CREATE FUNCTION dbo.HexToINT
(
@Value VARCHAR(8)
)
RETURNS INT
AS
BEGIN
DECLARE @I BIGINT
SET @I = CAST(CAST(RIGHT( UPPER( '00000000' + @Value ) , 8 )
AS BINARY(8)) AS BIGINT) - 3472328296227680304
SET @I=@I-((@I/16)&CAST(72340172838076673 AS BIGINT))*7
RETURN (
(@I&15)
+((@I/16)&240)
+((@I/256)&3840)
+((@I/4096)&61440)
+((@I/65536)&983040)
+((@I/1048576)&15728640)
+((@I/16777216)&251658240)
+((@I/72057594037927936)*268435456) -- cause an OF if > 0x80000000
)
END
GO
CREATE FUNCTION dbo.HexToSMALLINT
(
@Value VARCHAR(4)
)
RETURNS SMALLINT
AS
BEGIN
DECLARE @I INT
SET @I = CAST(CAST(RIGHT( UPPER( '0000' + @Value ) , 4 )
AS BINARY(4)) AS INT) - 808464432
SET @I=@I-(@I&269488144)*7/16
RETURN (
@I&255
+(@I&65280)/16
+(@I&16711680)/256
+(@I&2130706432)/4096
)
END
GO
