1 files changed, 46 insertions, 14 deletions

diff --git a/ext/misc/zorder.c b/ext/misc/zorder.c
index c385d3c3c..c4c5fcdc7 100644
--- a/ext/misc/zorder.c
+++ b/ext/misc/zorder.c
@@ -16,6 +16,17 @@
 **
 **      unzorder(Z,N,I)          Extract the I-th dimension from N-dimensional
 **                               Morton code Z.
+**
+** Compiling:
+**
+**   (linux)    gcc -fPIC -shared zorder.c -o zorder.so
+**   (mac)      clang -fPIC -dynamiclib zorder.c -o zorder.dylib
+**   (windows)  cl zorder.c -link -dll -out:zorder.dll
+**
+** Usage example:
+**
+**     .load ./zorder
+**     SELECT zorder(1,2,3,4);
 */
 #include "sqlite3ext.h"
 SQLITE_EXTENSION_INIT1
@@ -25,43 +36,53 @@ SQLITE_EXTENSION_INIT1
 /*
 ** Functions:     zorder(X0,X1,....)
 **
-** Convert integers X0, X1, ... into morton code.
+** Convert integers X0, X1, ... into morton code.  There must be at least
+** two arguments.  There may be no more than 24 arguments.
 **
-** The output is a signed 64-bit integer.  If any argument is too large,
-** an error is thrown.
+** The output is a signed 64-bit integer.  If any argument is too large
+** to be successfully encoded into a morton code, an error is raised.
 */
 static void zorderFunc(
   sqlite3_context *context,
   int argc,
   sqlite3_value **argv
 ){
-  sqlite3_int64 z, x[63];
+  sqlite3_int64 z, x[24];
   int i, j;
   z = 0;
+  if( argc<2 || argc>24 ){
+    sqlite3_result_error(context,
+       "zorder() needs between 2 and 24 arguments4", -1);
+    return;
+  }
   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;
-    }
+  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);
+      char *z = sqlite3_mprintf(
+        "the %r argument to zorder() (%lld) is too large "
+        "for a 64-bit %d-dimensional Morton code",
+        i+1, sqlite3_value_int64(argv[i]), argc);
+      sqlite3_result_error(context, z, -1);
+      sqlite3_free(z);
+      break;
     }
   }
 }
 
 
 /*
-** Functions:     unzorder(Z,N,I)
+** Function:     unzorder(Z,N,K)
 **
-** Assuming that Z is an N-dimensional Morton code, extract the I-th
-** dimension.
+** Assuming that Z is an N-dimensional Morton code, extract the K-th
+** dimension.  K is between 0 and N-1.  N must be between 2 and 24.
 */
 static void unzorderFunc(
   sqlite3_context *context,
@@ -72,7 +93,18 @@ static void unzorderFunc(
   int j, k;
   z = sqlite3_value_int64(argv[0]);
   n = sqlite3_value_int64(argv[1]);
+  if( n<2 || n>24 ){
+    sqlite3_result_error(context,
+      "N argument to unzorder(Z,N,K) should be between 2 and 24",
+      -1);
+    return;
+  }
   i = sqlite3_value_int64(argv[2]);
+  if( i<0 || i>=n ){
+    sqlite3_result_error(context,
+      "K argument to unzorder(Z,N,K) should be between 0 and N-1", -1);
+    return;
+  }
   x = 0;
   for(k=0, j=i; j<63; j+=n, k++){
     x |= ((z>>j)&1)<<k;