/ Artifact Content
SQLite training in Houston TX on 2019-11-05 (details)
Part of the 2019 Tcl Conference

• File ext/misc/zorder.c — part of check-in [a57a77dc] at 2018-02-09 20:49:15 on branch trunk — Add the zorder.c extension implementing zorder() and unzorder() SQL functions. (user: drh size: 2391) [more...]

``````/*
** 2018-02-09
**
** 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.
**
******************************************************************************
**
** SQL functions for z-order (Morton code) transformations.
**
**      zorder(X0,X0,..,xN)      Generate an N+1 dimension Morton code
**
**      unzorder(Z,N,I)          Extract the I-th dimension from N-dimensional
**                               Morton code Z.
*/
#include "sqlite3ext.h"
SQLITE_EXTENSION_INIT1
#include <assert.h>
#include <string.h>

/*
** Functions:     zorder(X0,X1,....)
**
** Convert integers X0, X1, ... into morton code.
**
** The output is a signed 64-bit integer.  If any argument is too large,
** an error is thrown.
*/
static void zorderFunc(
sqlite3_context *context,
int argc,
sqlite3_value **argv
){
sqlite3_int64 z, x[63];
int i, j;
z = 0;
for(i=0; i<argc; i++){
x[i] = sqlite3_value_int64(argv[i]);
}
if( argc>0 ){
for(i=0; i<63; i++){
j = i%argc;
z |= (x[j]&1)<<i;
x[j] >>= 1;
}
}
sqlite3_result_int64(context, z);
for(i=0; i<argc; i++){
if( x[i] ){
sqlite3_result_error(context, "parameter too large", -1);
}
}
}

/*
** Functions:     unzorder(Z,N,I)
**
** Assuming that Z is an N-dimensional Morton code, extract the I-th
** dimension.
*/
static void unzorderFunc(
sqlite3_context *context,
int argc,
sqlite3_value **argv
){
sqlite3_int64 z, n, i, x;
int j, k;
z = sqlite3_value_int64(argv[0]);
n = sqlite3_value_int64(argv[1]);
i = sqlite3_value_int64(argv[2]);
x = 0;
for(k=0, j=i; j<63; j+=n, k++){
x |= ((z>>j)&1)<<k;
}
sqlite3_result_int64(context, x);
}

#ifdef _WIN32
__declspec(dllexport)
#endif
int sqlite3_zorder_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, "zorder", -1, SQLITE_UTF8, 0,
zorderFunc, 0, 0);
if( rc==SQLITE_OK ){
rc = sqlite3_create_function(db, "unzorder", 3, SQLITE_UTF8, 0,
unzorderFunc, 0, 0);
}
return rc;
}
```
```