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Empress Extreme

Extreme 5

Adding Hexadecimal Conversion Functionality
As a Persistent Stored Module (PSM) to Empress

Introduction

The purpose of this technical note is two-fold:

Convert data to hexadecimal values
Demonstrate how to write a polymorphic function

This technical note will guide user through the steps that are needed to create one new function that will allow user to:

Convert integers to its equivalent hexadecimal string
Convert character data to its equivalent hexadecimal string

The respective function, built by using Empress SQL Persistent Stored Module (PSM) technology, is named:

to_hex

For example, SELECT command which incorporates the above function (id is a table attribute of an integer data type while a data is an attribute ofa character data type):

SELECT id, to_hex(id), data, to_hex(data) FROM t1 LIST

could generate the following results:

 
                                
                                    id: -2147483647
TO_HEX(id): 80000001
data: SMALL INTEGER
TO_HEX(data): 534d414c4c20494e5445474552

id: 2147483647
TO_HEX(id): 7fffffff
data: BIG INTEGER
TO_HEX(data): 42494720494e5445474552

Implementation

The basic algorithm is as follows:

convert integer data to its equivalent hexadecimal value via the C library sprintf.
convert character data to its equivalent hexadecimal value via the C library sprintf.

APPENDIX

The following script can be executed with EMPRESS RDBMS V8.62 installed on a UNIX system in order to acquire the above described functionality.

#!/bin/sh

if [ -z $EMPRESSPATH ]
then
 echo " This demo requires that EMPRESSPATH is set." 
 exit 1
fi

cat >  ./module.c < < EOM
#include < mscc.h> 
#include < usrfns.h> 
#include < stdio.h> 
#include < string.h> 

/*
*
* Par1: input: character data
* Par2: output: hexadecimal string
* Par3: control variable for input/output parameter 1
* Par4: control variable for output parameter 1
* Par5: status variable [whether or not function was alright, maxlength = 5]
* Par6: runtime name [filled in by Empress]
* Par7: external name of function [filled in by Empress]
* Par8: error message [maxlength is 256]
*/

GLOBAL_SHARED_FUNC void to_hex_char (
 char* input_str,
 char** out,
 long* in_ctrl1,
 long* out_ctrl1,
 char* sqlstate,
 char* rtname,
 char* extname,
 char* errmsg
 )
{
 char* buf 
 int len 
 int i 
 int j 

 /* Set the output to be null */
 *out_ctrl1 = -1L 
 *out = (char) 0 

 /* input_str should not be zero, but check just in case */
 if (input_str == 0 & &  *in_ctrl1 > = 0)
 {
 strcpy (sqlstate, " INPUT" ) 
 strcpy (errmsg,
 " Problem: INPUT string is null" ) 
 return 
 }
 /* If the first parameter is null, just return null */
 if (*in_ctrl1 == -1L)
 {
 strcpy (sqlstate, " INPUT" ) 
 strcpy (errmsg,
 " Problem: INPUT string is null" ) 
 return 
 }

 /* We want to allocate enough space for hexadecimal string
 * one input byte = 2 output bytes (ie: 5 = 05 ) */
 len = strlen (input_str) 
 buf = (char*) mspsm_malloc ((len *2) +1) 

 *out_ctrl1 = 0L 
 for (i = 0, j=0  i <  len  i++, j+=2)
 {
 sprintf (buf +j, " %2.2x" , *(input_str +i)) 
 }
 *out = buf 
}

/*
*
* Par1: input: integer data
* Par2: output: hexadecimal string
* Par3: control variable for input/output parameter 1
* Par4: control variable for output parameter 1
* Par5: status variable [whether or not function was okay, maxlength = 5]
* Par6: runtime name [filled in by Empress]
* Par7: external name of function [filled in by Empress]
* Par8: error message [maxlength is 256]
*/

GLOBAL_SHARED_FUNC void to_hex_int (
 gen_integer input_num,
 char** out,
 long* in_ctrl1,
 long* out_ctrl1,
 char* sqlstate,
 char* rtname,
 char* extname,
 char* errmsg
 )
{
 char* buf 

 /* Set the output to be null */
 *out_ctrl1 = -1L 
 *out = (char) 0 

 /* If the first parameter is null, just return null */
 if (*in_ctrl1 == -1L)
 {
 strcpy (sqlstate, " INPUT" ) 
 strcpy (errmsg,
 " Problem: INPUT integer is null" ) 
 return 
 }

 /* one input byte = 2 output bytes (ie: 5 = 05 ) */
 buf = (char*) mspsm_malloc ((sizeof(gen_integer) *2) +1) 

 *out_ctrl1 = 0L 
 if (input_num < = (unsigned long) 0xff)
 sprintf (buf, " %2.2lx" , input_num) 
 elif (input_num < = (unsigned long) 0xffff)
 sprintf (buf, " %4.4lx" , input_num) 
 elif (input_num < = (unsigned long) 0xffffff)
 sprintf (buf, " %6.6lx" , input_num) 
 elif (input_num < = (unsigned long) 0xffffffff)
 sprintf (buf, " %8.8lx" , input_num) 
 else
 {
 *out_ctrl1 = -1L 
 buf[0] = '\0' 
 }
 *out = buf 
}
EOM

echo " Creating the shared object 'module.dll'." 
emppsmcc -o module.dll module.c


if [ -d db ]
then
 echo " Removing 'db'" 
 emprmdb db
fi
echo " Creating 'db'" 
empmkdb db

empbatch db < < EOM
!echo " Creating and defining module 'Hexadecimal'." 
CREATE MODULE Hexadecimal
 FUNCTION to_hex (GENERIC CHAR)
 RETURNS GENERIC CHAR
 EXTERNAL NAME to_hex_char
 PARAMETER STYLE SQL 
 FUNCTION to_hex (GENERIC INTEGER)
 RETURNS GENERIC CHAR
 EXTERNAL NAME to_hex_int
 PARAMETER STYLE SQL 
END MODULE 
CREATE TABLE t1 (id longinteger, data nlstext(80,1024,1024,1)) 
INSERT INTO t1 VALUES (
-2147483647, " SMALL INTEGER" ,
2147483647, " BIG INTEGER" ) 

UPDATE MODULE Hexadecimal FROM './module.dll' 

SELECT to_hex(id), id, to_hex(data), data FROM t1 LIST 
EOM

rm module.c module.dll

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