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T-sql base64

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CREATE FUNCTION base64_decode
(
@encoded_text varchar(8000)
)
RETURNS
varchar(6000)
AS BEGIN
--local variables
DECLARE
@output varchar(8000),
@block_start int,
@encoded_length int,
@decoded_length int,
@mapr binary(122)
--IF @encoded_text COLLATE LATIN1_GENERAL_BIN
-- LIKE '%[^ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789 /=]%'
-- COLLATE LATIN1_GENERAL_BIN
-- RETURN NULL
--IF LEN(@encoded_text) & 3 > 0
-- RETURN NULL
SET @output = ''
-- The nth byte of @mapr contains the base64 value
-- of the character with an ASCII value of n.
-- EG, 65th byte = 0x00 = 0 = value of 'A'
SET @mapr =
0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF -- 1-33
0xFFFFFFFFFFFFFFFFFFFF3EFFFFFF3F3435363738393A3B3C3DFFFFFF00FFFFFF -- 33-64
0x000102030405060708090A0B0C0D0E0F10111213141516171819FFFFFFFFFFFF -- 65-96
0x1A1B1C1D1E1F202122232425262728292A2B2C2D2E2F30313233 -- 97-122
--get the number of blocks to be decoded
SET @encoded_length = LEN(@encoded_text)
SET @decoded_length = @encoded_length / 4 * 3
--for each block
SET @block_start = 1
WHILE @block_start < @encoded_length BEGIN
--decode the block and add to output
--BINARY values between 1 and 4 bytes can be implicitly cast to INT
SET @output = @output CAST(CAST(CAST(
substring( @mapr, ascii( substring( @encoded_text, @block_start , 1) ), 1) * 262144
substring( @mapr, ascii( substring( @encoded_text, @block_start 1, 1) ), 1) * 4096
substring( @mapr, ascii( substring( @encoded_text, @block_start 2, 1) ), 1) * 64
substring( @mapr, ascii( substring( @encoded_text, @block_start 3, 1) ), 1)
AS INTEGER) AS BINARY(3)) AS VARCHAR(3))
SET @block_start = @block_start 4
END
IF RIGHT(@encoded_text, 2) = '=='
SET @decoded_length = @decoded_length - 2
ELSE IF RIGHT(@encoded_text, 1) = '='
SET @decoded_length = @decoded_length - 1
--IF SUBSTRING(@output, @decoded_length, 1) = CHAR(0)
-- SET @decoded_length = @decoded_length - 1
--return the decoded string
RETURN LEFT(@output, @decoded_length)
END
GO

IF object_id('[dbo].[base64_encode]') IS NOT NULL
DROP FUNCTION [dbo].[base64_encode]
GO

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