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