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to the (unused) zorder extension function. [forum:/forumpost/e3f1ede174|Forum post e3f1ede174] FossilOrigin-Name: 6bb717acf706e6ffd4671660ca78237e6a42863f344518e6d21065bf735f971e
135 lines
3.4 KiB
C
135 lines
3.4 KiB
C
/*
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** 2018-02-09
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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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** SQL functions for z-order (Morton code) transformations.
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**
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** zorder(X0,X0,..,xN) Generate an N+1 dimension Morton code
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**
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** unzorder(Z,N,I) Extract the I-th dimension from N-dimensional
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** Morton code Z.
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**
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** Compiling:
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**
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** (linux) gcc -fPIC -shared zorder.c -o zorder.so
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** (mac) clang -fPIC -dynamiclib zorder.c -o zorder.dylib
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** (windows) cl zorder.c -link -dll -out:zorder.dll
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**
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** Usage example:
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**
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** .load ./zorder
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** SELECT zorder(1,2,3,4);
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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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/*
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** Functions: zorder(X0,X1,....)
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**
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** Convert integers X0, X1, ... into morton code. There must be at least
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** two arguments. There may be no more than 24 arguments.
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**
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** The output is a signed 64-bit integer. If any argument is too large
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** to be successfully encoded into a morton code, an error is raised.
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*/
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static void zorderFunc(
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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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sqlite3_int64 z, x[24];
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int i, j;
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z = 0;
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if( argc<2 || argc>24 ){
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sqlite3_result_error(context,
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"zorder() needs between 2 and 24 arguments4", -1);
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return;
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}
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for(i=0; i<argc; i++){
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x[i] = sqlite3_value_int64(argv[i]);
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}
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for(i=0; i<63; i++){
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j = i%argc;
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z |= (x[j]&1)<<i;
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x[j] >>= 1;
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}
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sqlite3_result_int64(context, z);
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for(i=0; i<argc; i++){
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if( x[i] ){
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char *z = sqlite3_mprintf(
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"the %r argument to zorder() (%lld) is too large "
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"for a 64-bit %d-dimensional Morton code",
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i+1, sqlite3_value_int64(argv[i]), argc);
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sqlite3_result_error(context, z, -1);
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sqlite3_free(z);
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break;
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}
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}
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}
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/*
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** Function: unzorder(Z,N,K)
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**
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** Assuming that Z is an N-dimensional Morton code, extract the K-th
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** dimension. K is between 0 and N-1. N must be between 2 and 24.
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*/
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static void unzorderFunc(
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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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sqlite3_int64 z, n, i, x;
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int j, k;
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z = sqlite3_value_int64(argv[0]);
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n = sqlite3_value_int64(argv[1]);
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if( n<2 || n>24 ){
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sqlite3_result_error(context,
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"N argument to unzorder(Z,N,K) should be between 2 and 24",
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-1);
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return;
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}
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i = sqlite3_value_int64(argv[2]);
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if( i<0 || i>=n ){
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sqlite3_result_error(context,
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"K argument to unzorder(Z,N,K) should be between 0 and N-1", -1);
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return;
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}
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x = 0;
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for(k=0, j=i; j<63; j+=n, k++){
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x |= ((z>>j)&1)<<k;
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}
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sqlite3_result_int64(context, x);
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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_zorder_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, "zorder", -1, SQLITE_UTF8, 0,
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zorderFunc, 0, 0);
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if( rc==SQLITE_OK ){
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rc = sqlite3_create_function(db, "unzorder", 3, SQLITE_UTF8, 0,
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unzorderFunc, 0, 0);
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}
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return rc;
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}
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