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/*
** 2024-05-24
**
** The author disclaims copyright to this source code. In place of
** a legal notice, here is a blessing:
**
** May you do good and not evil.
** May you find forgiveness for yourself and forgive others.
** May you share freely, never taking more than you give.
**
******************************************************************************
**
** An SQL function that return pseudo-random non-negative integers.
**
** SELECT stmtrand(123);
**
** A special feature of this function is that the same sequence of random
** integers is returned for each invocation of the statement. This makes
** the results repeatable, and hence useful for testing. The argument is
** an integer which is the seed for the random number sequence. The seed
** is used by the first invocation of this function only and is ignored
** for all subsequent calls within the same statement.
**
** Resetting a statement (sqlite3_reset()) also resets the random number
** sequence.
*/
#include "sqlite3ext.h"
SQLITE_EXTENSION_INIT1
#include <assert.h>
#include <string.h>
/* State of the pseudo-random number generator */
typedef struct Stmtrand {
unsigned int x, y;
} Stmtrand;
/* auxdata key */
#define STMTRAND_KEY (-4418371)
/*
** Function: stmtrand(SEED)
**
** Return a pseudo-random number.
*/
static void stmtrandFunc(
sqlite3_context *context,
int argc,
sqlite3_value **argv
){
Stmtrand *p;
p = (Stmtrand*)sqlite3_get_auxdata(context, STMTRAND_KEY);
if( p==0 ){
unsigned int seed;
p = sqlite3_malloc( sizeof(*p) );
if( p==0 ){
sqlite3_result_error_nomem(context);
return;
}
if( argc>=1 ){
seed = (unsigned int)sqlite3_value_int(argv[0]);
}else{
seed = 0;
}
p->x = seed | 1;
p->y = seed;
sqlite3_set_auxdata(context, STMTRAND_KEY, p, sqlite3_free);
p = (Stmtrand*)sqlite3_get_auxdata(context, STMTRAND_KEY);
if( p==0 ){
sqlite3_result_error_nomem(context);
return;
}
}
p->x = (p->x>>1) ^ ((1+~(p->x&1)) & 0xd0000001);
p->y = p->y*1103515245 + 12345;
sqlite3_result_int(context, (int)((p->x ^ p->y)&0x7fffffff));
}
#ifdef _WIN32
__declspec(dllexport)
#endif
int sqlite3_stmtrand_init(
sqlite3 *db,
char **pzErrMsg,
const sqlite3_api_routines *pApi
){
int rc = SQLITE_OK;
SQLITE_EXTENSION_INIT2(pApi);
(void)pzErrMsg; /* Unused parameter */
rc = sqlite3_create_function(db, "stmtrand", 1, SQLITE_UTF8, 0,
stmtrandFunc, 0, 0);
if( rc==SQLITE_OK ){
rc = sqlite3_create_function(db, "stmtrand", 0, SQLITE_UTF8, 0,
stmtrandFunc, 0, 0);
}
return rc;
}
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