/*

 ** 2002 February 23

 **

 ** 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.

 **

 *************************************************************************

 ** This file contains the C functions that implement various SQL

 ** functions of SQLite.  

 **

 ** There is only one exported symbol in this file - the function

 ** sqliteRegisterBuildinFunctions() found at the bottom of the file.

 ** All other code has file scope.

 **

 ** $Id$

 */

 #include "sqliteInt.h"

 #include <ctype.h>

 #include <stdlib.h>

 #include <assert.h>

 #include "vdbeInt.h"

 /*

 ** Return the collating function associated with a function.

 */

 static CollSeq *sqlite3GetFuncCollSeq(sqlite3_context *context){

   return context->pColl;

 }

 /*

 ** Implementation of the non-aggregate min() and max() functions

 */

 static void minmaxFunc(

   sqlite3_context *context,

   int argc,

   sqlite3_value **argv

 ){

   int i;

   int mask;    /* 0 for min() or 0xffffffff for max() */

   int iBest;

   CollSeq *pColl;

   if( argc==0 ) return;

   mask = sqlite3_user_data(context)==0 ? 0 : -1;

   pColl = sqlite3GetFuncCollSeq(context);

   assert( pColl );

   assert( mask==-1 || mask==0 );

   iBest = 0;

   if( sqlite3_value_type(argv[0])==SQLITE_NULL ) return;

   for(i=1; i<argc; i++){

     if( sqlite3_value_type(argv[i])==SQLITE_NULL ) return;

     if( (sqlite3MemCompare(argv[iBest], argv[i], pColl)^mask)>=0 ){

       iBest = i;

     }

   }

   sqlite3_result_value(context, argv[iBest]);

 }

 /*

 ** Return the type of the argument.

 */

 static void typeofFunc(

   sqlite3_context *context,

   int argc,

   sqlite3_value **argv

 ){

   const char *z = 0;

   switch( sqlite3_value_type(argv[0]) ){

     case SQLITE_NULL:    z = "null";    break;

     case SQLITE_INTEGER: z = "integer"; break;

     case SQLITE_TEXT:    z = "text";    break;

     case SQLITE_FLOAT:   z = "real";    break;

     case SQLITE_BLOB:    z = "blob";    break;

   }

   sqlite3_result_text(context, z, -1, SQLITE_STATIC);

 }

 /*

 ** Implementation of the length() function

 */

 static void lengthFunc(

   sqlite3_context *context,

   int argc,

   sqlite3_value **argv

 ){

   int len;

   assert( argc==1 );

   switch( sqlite3_value_type(argv[0]) ){

     case SQLITE_BLOB:

     case SQLITE_INTEGER:

     case SQLITE_FLOAT: {

       sqlite3_result_int(context, sqlite3_value_bytes(argv[0]));

       break;

     }

     case SQLITE_TEXT: {

       const unsigned char *z = sqlite3_value_text(argv[0]);

       if( z==0 ) return;

       len = 0;

       while( *z ){

         len++;

         SQLITE_SKIP_UTF8(z);

       }

       sqlite3_result_int(context, len);

       break;

     }

     default: {

       sqlite3_result_null(context);

       break;

     }

   }

 }

 /*

 ** Implementation of the abs() function

 */

 static void absFunc(sqlite3_context *context, int argc, sqlite3_value **argv){

   assert( argc==1 );

   switch( sqlite3_value_type(argv[0]) ){

     case SQLITE_INTEGER: {

       i64 iVal = sqlite3_value_int64(argv[0]);

       if( iVal<0 ){

         if( (iVal<<1)==0 ){

           sqlite3_result_error(context, "integer overflow", -1);

           return;

         }

         iVal = -iVal;

       } 

       sqlite3_result_int64(context, iVal);

       break;

     }

     case SQLITE_NULL: {

       sqlite3_result_null(context);

       break;

     }

     default: {

       double rVal = sqlite3_value_double(argv[0]);

       if( rVal<0 ) rVal = -rVal;

       sqlite3_result_double(context, rVal);

       break;

     }

   }

 }

 /*

 ** Implementation of the substr() function.

 **

 ** substr(x,p1,p2)  returns p2 characters of x[] beginning with p1.

 ** p1 is 1-indexed.  So substr(x,1,1) returns the first character

 ** of x.  If x is text, then we actually count UTF-8 characters.

 ** If x is a blob, then we count bytes.

 **

 ** If p1 is negative, then we begin abs(p1) from the end of x[].

 */

 static void substrFunc(

   sqlite3_context *context,

   int argc,

   sqlite3_value **argv

 ){

   const unsigned char *z;

   const unsigned char *z2;

   int len;

   int p0type;

   i64 p1, p2;

   assert( argc==3 );

   p0type = sqlite3_value_type(argv[0]);

   if( p0type==SQLITE_BLOB ){

     len = sqlite3_value_bytes(argv[0]);

     z = sqlite3_value_blob(argv[0]);

     if( z==0 ) return;

     assert( len==sqlite3_value_bytes(argv[0]) );

   }else{

     z = sqlite3_value_text(argv[0]);

     if( z==0 ) return;

     len = 0;

     for(z2=z; *z2; len++){

       SQLITE_SKIP_UTF8(z2);

     }

   }

   p1 = sqlite3_value_int(argv[1]);

   p2 = sqlite3_value_int(argv[2]);

   if( p1<0 ){

     p1 += len;

     if( p1<0 ){

       p2 += p1;

       p1 = 0;

     }

   }else if( p1>0 ){

     p1--;

   }

   if( p1+p2>len ){

     p2 = len-p1;

   }

   if( p0type!=SQLITE_BLOB ){

     while( *z && p1 ){

       SQLITE_SKIP_UTF8(z);

       p1--;

     }

     for(z2=z; *z2 && p2; p2--){

       SQLITE_SKIP_UTF8(z2);

     }

     sqlite3_result_text(context, (char*)z, z2-z, SQLITE_TRANSIENT);

   }else{

     if( p2<0 ) p2 = 0;

     sqlite3_result_blob(context, (char*)&z[p1], p2, SQLITE_TRANSIENT);

   }

 }

 /*

 ** Implementation of the round() function

 */

 static void roundFunc(sqlite3_context *context, int argc, sqlite3_value **argv){

   int n = 0;

   double r;

   char zBuf[500];  /* larger than the %f representation of the largest double */

   assert( argc==1 || argc==2 );

   if( argc==2 ){

     if( SQLITE_NULL==sqlite3_value_type(argv[1]) ) return;

     n = sqlite3_value_int(argv[1]);

     if( n>30 ) n = 30;

     if( n<0 ) n = 0;

   }

   if( sqlite3_value_type(argv[0])==SQLITE_NULL ) return;

   r = sqlite3_value_double(argv[0]);

   sqlite3_snprintf(sizeof(zBuf),zBuf,"%.*f",n,r);

   sqlite3AtoF(zBuf, &r);

   sqlite3_result_double(context, r);

 }

 /*

 ** Allocate nByte bytes of space using sqlite3_malloc(). If the

 ** allocation fails, call sqlite3_result_error_nomem() to notify

 ** the database handle that malloc() has failed.

 */

 static void *contextMalloc(sqlite3_context *context, int nByte){

   char *z = sqlite3_malloc(nByte);

   if( !z && nByte>0 ){

     sqlite3_result_error_nomem(context);

   }

   return z;

 }

 /*

 ** Implementation of the upper() and lower() SQL functions.

 */

 static void upperFunc(sqlite3_context *context, int argc, sqlite3_value **argv){

   char *z1;

   const char *z2;

   int i, n;

   if( argc<1 || SQLITE_NULL==sqlite3_value_type(argv[0]) ) return;

   z2 = (char*)sqlite3_value_text(argv[0]);

   n = sqlite3_value_bytes(argv[0]);

   /* Verify that the call to _bytes() does not invalidate the _text() pointer */

   assert( z2==(char*)sqlite3_value_text(argv[0]) );

   if( z2 ){

     z1 = contextMalloc(context, n+1);

     if( z1 ){

       memcpy(z1, z2, n+1);

       for(i=0; z1[i]; i++){

         z1[i] = toupper(z1[i]);

       }

       sqlite3_result_text(context, z1, -1, sqlite3_free);

     }

   }

 }

 static void lowerFunc(sqlite3_context *context, int argc, sqlite3_value **argv){

   char *z1;

   const char *z2;

   int i, n;

   if( argc<1 || SQLITE_NULL==sqlite3_value_type(argv[0]) ) return;

   z2 = (char*)sqlite3_value_text(argv[0]);

   n = sqlite3_value_bytes(argv[0]);

   /* Verify that the call to _bytes() does not invalidate the _text() pointer */

   assert( z2==(char*)sqlite3_value_text(argv[0]) );

   if( z2 ){

     z1 = contextMalloc(context, n+1);

     if( z1 ){

       memcpy(z1, z2, n+1);

       for(i=0; z1[i]; i++){

         z1[i] = tolower(z1[i]);

       }

       sqlite3_result_text(context, z1, -1, sqlite3_free);

     }

   }

 }

 /*

 ** Implementation of the IFNULL(), NVL(), and COALESCE() functions.  

 ** All three do the same thing.  They return the first non-NULL

 ** argument.

 */

 static void ifnullFunc(

   sqlite3_context *context,

   int argc,

   sqlite3_value **argv

 ){

   int i;

   for(i=0; i<argc; i++){

     if( SQLITE_NULL!=sqlite3_value_type(argv[i]) ){

       sqlite3_result_value(context, argv[i]);

       break;

     }

   }

 }

 /*

 ** Implementation of random().  Return a random integer.  

 */

 static void randomFunc(

   sqlite3_context *context,

   int argc,

   sqlite3_value **argv

 ){

   sqlite_int64 r;

   sqlite3Randomness(sizeof(r), &r);

   if( (r<<1)==0 ) r = 0;  /* Prevent 0x8000.... as the result so that we */

                           /* can always do abs() of the result */

   sqlite3_result_int64(context, r);

 }

 /*

 ** Implementation of randomblob(N).  Return a random blob

 ** that is N bytes long.

 */

 static void randomBlob(

   sqlite3_context *context,

   int argc,

   sqlite3_value **argv

 ){

   int n;

   unsigned char *p;

   assert( argc==1 );

   n = sqlite3_value_int(argv[0]);

   if( n<1 ){

     n = 1;

   }

   if( n>SQLITE_MAX_LENGTH ){

     sqlite3_result_error_toobig(context);

     return;

   }

   p = contextMalloc(context, n);

   if( p ){

     sqlite3Randomness(n, p);

     sqlite3_result_blob(context, (char*)p, n, sqlite3_free);

   }

 }

 /*

 ** Implementation of the last_insert_rowid() SQL function.  The return

 ** value is the same as the sqlite3_last_insert_rowid() API function.

 */

 static void last_insert_rowid(

   sqlite3_context *context, 

   int arg, 

   sqlite3_value **argv

 ){

   sqlite3 *db = sqlite3_user_data(context);

   sqlite3_result_int64(context, sqlite3_last_insert_rowid(db));

 }

 /*

 ** Implementation of the changes() SQL function.  The return value is the

 ** same as the sqlite3_changes() API function.

 */

 static void changes(

   sqlite3_context *context,

   int arg,

   sqlite3_value **argv

 ){

   sqlite3 *db = sqlite3_user_data(context);

   sqlite3_result_int(context, sqlite3_changes(db));

 }

 /*

 ** Implementation of the total_changes() SQL function.  The return value is

 ** the same as the sqlite3_total_changes() API function.

 */

 static void total_changes(

   sqlite3_context *context,

   int arg,

   sqlite3_value **argv

 ){

   sqlite3 *db = sqlite3_user_data(context);

   sqlite3_result_int(context, sqlite3_total_changes(db));

 }

 /*

 ** A structure defining how to do GLOB-style comparisons.

 */

 struct compareInfo {

   u8 matchAll;

   u8 matchOne;

   u8 matchSet;

   u8 noCase;

 };

 static const struct compareInfo globInfo = { '*', '?', '[', 0 };

 /* The correct SQL-92 behavior is for the LIKE operator to ignore

 ** case.  Thus  'a' LIKE 'A' would be true. */

 static const struct compareInfo likeInfoNorm = { '%', '_',   0, 1 };

 /* If SQLITE_CASE_SENSITIVE_LIKE is defined, then the LIKE operator

 ** is case sensitive causing 'a' LIKE 'A' to be false */

 static const struct compareInfo likeInfoAlt = { '%', '_',   0, 0 };

 /*

 ** Compare two UTF-8 strings for equality where the first string can

 ** potentially be a "glob" expression.  Return true (1) if they

 ** are the same and false (0) if they are different.

 **

 ** Globbing rules:

 **

 **      '*'       Matches any sequence of zero or more characters.

 **

 **      '?'       Matches exactly one character.

 **

 **     [...]      Matches one character from the enclosed list of

 **                characters.

 **

 **     [^...]     Matches one character not in the enclosed list.

 **

 ** With the [...] and [^...] matching, a ']' character can be included

 ** in the list by making it the first character after '[' or '^'.  A

 ** range of characters can be specified using '-'.  Example:

 ** "[a-z]" matches any single lower-case letter.  To match a '-', make

 ** it the last character in the list.

 **

 ** This routine is usually quick, but can be N**2 in the worst case.

 **

 ** Hints: to match '*' or '?', put them in "[]".  Like this:

 **

 **         abc[*]xyz        Matches "abc*xyz" only

 */

 static int patternCompare(

   const u8 *zPattern,              /* The glob pattern */

   const u8 *zString,               /* The string to compare against the glob */

   const struct compareInfo *pInfo, /* Information about how to do the compare */

   const int esc                    /* The escape character */

 ){

   int c, c2;

   int invert;

   int seen;

   u8 matchOne = pInfo->matchOne;

   u8 matchAll = pInfo->matchAll;

   u8 matchSet = pInfo->matchSet;

   u8 noCase = pInfo->noCase; 

   int prevEscape = 0;     /* True if the previous character was 'escape' */

   while( (c = sqlite3Utf8Read(zPattern,0,&zPattern))!=0 ){

     if( !prevEscape && c==matchAll ){

       while( (c=sqlite3Utf8Read(zPattern,0,&zPattern)) == matchAll

                || c == matchOne ){

         if( c==matchOne && sqlite3Utf8Read(zString, 0, &zString)==0 ){

           return 0;

         }

       }

       if( c==0 ){

         return 1;

       }else if( c==esc ){

         c = sqlite3Utf8Read(zPattern, 0, &zPattern);

         if( c==0 ){

           return 0;

         }

       }else if( c==matchSet ){

         assert( esc==0 );         /* This is GLOB, not LIKE */

         assert( matchSet<0x80 );  /* '[' is a single-byte character */

         while( *zString && patternCompare(&zPattern[-1],zString,pInfo,esc)==0 ){

           SQLITE_SKIP_UTF8(zString);

         }

         return *zString!=0;

       }

       while( (c2 = sqlite3Utf8Read(zString,0,&zString))!=0 ){

         if( noCase ){

           c2 = c2<0x80 ? sqlite3UpperToLower[c2] : c2;

           c = c<0x80 ? sqlite3UpperToLower[c] : c;

           while( c2 != 0 && c2 != c ){

             c2 = sqlite3Utf8Read(zString, 0, &zString);

             if( c2<0x80 ) c2 = sqlite3UpperToLower[c2];

           }

         }else{

           while( c2 != 0 && c2 != c ){

             c2 = sqlite3Utf8Read(zString, 0, &zString);

           }

         }

         if( c2==0 ) return 0;

         if( patternCompare(zPattern,zString,pInfo,esc) ) return 1;

       }

       return 0;

     }else if( !prevEscape && c==matchOne ){

       if( sqlite3Utf8Read(zString, 0, &zString)==0 ){

         return 0;

       }

     }else if( c==matchSet ){

       int prior_c = 0;

       assert( esc==0 );    /* This only occurs for GLOB, not LIKE */

       seen = 0;

       invert = 0;

       c = sqlite3Utf8Read(zString, 0, &zString);

       if( c==0 ) return 0;

       c2 = sqlite3Utf8Read(zPattern, 0, &zPattern);

       if( c2=='^' ){

         invert = 1;

         c2 = sqlite3Utf8Read(zPattern, 0, &zPattern);

       }

       if( c2==']' ){

         if( c==']' ) seen = 1;

         c2 = sqlite3Utf8Read(zPattern, 0, &zPattern);

       }

       while( c2 && c2!=']' ){

         if( c2=='-' && zPattern[0]!=']' && zPattern[0]!=0 && prior_c>0 ){

           c2 = sqlite3Utf8Read(zPattern, 0, &zPattern);

           if( c>=prior_c && c<=c2 ) seen = 1;

           prior_c = 0;

         }else{

           if( c==c2 ){

             seen = 1;

           }

           prior_c = c2;

         }

         c2 = sqlite3Utf8Read(zPattern, 0, &zPattern);

       }

       if( c2==0 || (seen ^ invert)==0 ){

         return 0;

       }

     }else if( esc==c && !prevEscape ){

       prevEscape = 1;

     }else{

       c2 = sqlite3Utf8Read(zString, 0, &zString);

       if( noCase ){

         c = c<0x80 ? sqlite3UpperToLower[c] : c;

         c2 = c2<0x80 ? sqlite3UpperToLower[c2] : c2;

       }

       if( c!=c2 ){

         return 0;

       }

       prevEscape = 0;

     }

   }

   return *zString==0;

 }

 /*

 ** Count the number of times that the LIKE operator (or GLOB which is

 ** just a variation of LIKE) gets called.  This is used for testing

 ** only.

 */

 #ifdef SQLITE_TEST

 int sqlite3_like_count = 0;

 #endif

 /*

 ** Implementation of the like() SQL function.  This function implements

 ** the build-in LIKE operator.  The first argument to the function is the

 ** pattern and the second argument is the string.  So, the SQL statements:

 **

 **       A LIKE B

 **

 ** is implemented as like(B,A).

 **

 ** This same function (with a different compareInfo structure) computes

 ** the GLOB operator.

 */

 static void likeFunc(

   sqlite3_context *context, 

   int argc, 

   sqlite3_value **argv

 ){

   const unsigned char *zA, *zB;

   int escape = 0;

   zB = sqlite3_value_text(argv[0]);

   zA = sqlite3_value_text(argv[1]);

   /* Limit the length of the LIKE or GLOB pattern to avoid problems

   ** of deep recursion and N*N behavior in patternCompare().

   */

   if( sqlite3_value_bytes(argv[0])>SQLITE_MAX_LIKE_PATTERN_LENGTH ){

     sqlite3_result_error(context, "LIKE or GLOB pattern too complex", -1);

     return;

   }

   assert( zB==sqlite3_value_text(argv[0]) );  /* Encoding did not change */

   if( argc==3 ){

     /* The escape character string must consist of a single UTF-8 character.

     ** Otherwise, return an error.

     */

     const unsigned char *zEsc = sqlite3_value_text(argv[2]);

     if( zEsc==0 ) return;

     if( sqlite3Utf8CharLen((char*)zEsc, -1)!=1 ){

       sqlite3_result_error(context, 

           "ESCAPE expression must be a single character", -1);

       return;

     }

     escape = sqlite3Utf8Read(zEsc, 0, &zEsc);

   }

   if( zA && zB ){

     struct compareInfo *pInfo = sqlite3_user_data(context);

 #ifdef SQLITE_TEST

     sqlite3_like_count++;

 #endif

     sqlite3_result_int(context, patternCompare(zB, zA, pInfo, escape));

   }

 }

 /*

 ** Implementation of the NULLIF(x,y) function.  The result is the first

 ** argument if the arguments are different.  The result is NULL if the

 ** arguments are equal to each other.

 */

 static void nullifFunc(

   sqlite3_context *context,

   int argc,

   sqlite3_value **argv

 ){

   CollSeq *pColl = sqlite3GetFuncCollSeq(context);

   if( sqlite3MemCompare(argv[0], argv[1], pColl)!=0 ){

     sqlite3_result_value(context, argv[0]);

   }

 }

 /*

 ** Implementation of the VERSION(*) function.  The result is the version

 ** of the SQLite library that is running.

 */

 static void versionFunc(

   sqlite3_context *context,

   int argc,

   sqlite3_value **argv

 ){

   sqlite3_result_text(context, sqlite3_version, -1, SQLITE_STATIC);

 }

 /* Array for converting from half-bytes (nybbles) into ASCII hex

 ** digits. */

 static const char hexdigits[] = {

   '0', '1', '2', '3', '4', '5', '6', '7',

   '8', '9', 'A', 'B', 'C', 'D', 'E', 'F' 

 };

 /*

 ** EXPERIMENTAL - This is not an official function.  The interface may

 ** change.  This function may disappear.  Do not write code that depends

 ** on this function.

 **

 ** Implementation of the QUOTE() function.  This function takes a single

 ** argument.  If the argument is numeric, the return value is the same as

 ** the argument.  If the argument is NULL, the return value is the string

 ** "NULL".  Otherwise, the argument is enclosed in single quotes with

 ** single-quote escapes.

 */

 static void quoteFunc(sqlite3_context *context, int argc, sqlite3_value **argv){

   if( argc<1 ) return;

   switch( sqlite3_value_type(argv[0]) ){

     case SQLITE_NULL: {

       sqlite3_result_text(context, "NULL", 4, SQLITE_STATIC);

       break;

     }

     case SQLITE_INTEGER:

     case SQLITE_FLOAT: {

       sqlite3_result_value(context, argv[0]);

       break;

     }

     case SQLITE_BLOB: {

       char *zText = 0;

       char const *zBlob = sqlite3_value_blob(argv[0]);

       int nBlob = sqlite3_value_bytes(argv[0]);

       assert( zBlob==sqlite3_value_blob(argv[0]) ); /* No encoding change */

       if( 2*nBlob+4>SQLITE_MAX_LENGTH ){

         sqlite3_result_error_toobig(context);

         return;

       }

       zText = (char *)contextMalloc(context, (2*nBlob)+4); 

       if( zText ){

         int i;

         for(i=0; i<nBlob; i++){

           zText[(i*2)+2] = hexdigits[(zBlob[i]>>4)&0x0F];

           zText[(i*2)+3] = hexdigits[(zBlob[i])&0x0F];

         }

         zText[(nBlob*2)+2] = '\'';

         zText[(nBlob*2)+3] = '\0';

         zText[0] = 'X';

         zText[1] = '\'';

         sqlite3_result_text(context, zText, -1, SQLITE_TRANSIENT);

         sqlite3_free(zText);

       }

       break;

     }

     case SQLITE_TEXT: {

       int i,j;

       u64 n;

       const unsigned char *zArg = sqlite3_value_text(argv[0]);

       char *z;

       if( zArg==0 ) return;

       for(i=0, n=0; zArg[i]; i++){ if( zArg[i]=='\'' ) n++; }

       if( i+n+3>SQLITE_MAX_LENGTH ){

         sqlite3_result_error_toobig(context);

         return;

       }

       z = contextMalloc(context, i+n+3);

       if( z ){

         z[0] = '\'';

         for(i=0, j=1; zArg[i]; i++){

           z[j++] = zArg[i];

           if( zArg[i]=='\'' ){

             z[j++] = '\'';

           }

         }

         z[j++] = '\'';

         z[j] = 0;

         sqlite3_result_text(context, z, j, sqlite3_free);

       }

     }

   }

 }

 /*

 ** The hex() function.  Interpret the argument as a blob.  Return

 ** a hexadecimal rendering as text.

 */

 static void hexFunc(

   sqlite3_context *context,

   int argc,

   sqlite3_value **argv

 ){

   int i, n;

   const unsigned char *pBlob;

   char *zHex, *z;

   assert( argc==1 );

   pBlob = sqlite3_value_blob(argv[0]);

   n = sqlite3_value_bytes(argv[0]);

   if( n*2+1>SQLITE_MAX_LENGTH ){

     sqlite3_result_error_toobig(context);

     return;

   }

   assert( pBlob==sqlite3_value_blob(argv[0]) );  /* No encoding change */

   z = zHex = contextMalloc(context, n*2 + 1);

   if( zHex ){

     for(i=0; i<n; i++, pBlob++){

       unsigned char c = *pBlob;

       *(z++) = hexdigits[(c>>4)&0xf];

       *(z++) = hexdigits[c&0xf];

     }

     *z = 0;

     sqlite3_result_text(context, zHex, n*2, sqlite3_free);

   }

 }

 /*

 ** The zeroblob(N) function returns a zero-filled blob of size N bytes.

 */

 static void zeroblobFunc(

   sqlite3_context *context,

   int argc,

   sqlite3_value **argv

 ){

   i64 n;

   assert( argc==1 );

   n = sqlite3_value_int64(argv[0]);

   if( n>SQLITE_MAX_LENGTH ){

     sqlite3_result_error_toobig(context);

   }else{

     sqlite3_result_zeroblob(context, n);

   }

 }

 /*

 ** The replace() function.  Three arguments are all strings: call

 ** them A, B, and C. The result is also a string which is derived

 ** from A by replacing every occurance of B with C.  The match

 ** must be exact.  Collating sequences are not used.

 */

 static void replaceFunc(

   sqlite3_context *context,

   int argc,

   sqlite3_value **argv

 ){

   const unsigned char *zStr;        /* The input string A */

   const unsigned char *zPattern;    /* The pattern string B */

   const unsigned char *zRep;        /* The replacement string C */

   unsigned char *zOut;              /* The output */

   int nStr;                /* Size of zStr */

   int nPattern;            /* Size of zPattern */

   int nRep;                /* Size of zRep */

   i64 nOut;                /* Maximum size of zOut */

   int loopLimit;           /* Last zStr[] that might match zPattern[] */

   int i, j;                /* Loop counters */

   assert( argc==3 );

   zStr = sqlite3_value_text(argv[0]);

   if( zStr==0 ) return;

   nStr = sqlite3_value_bytes(argv[0]);

   assert( zStr==sqlite3_value_text(argv[0]) );  /* No encoding change */

   zPattern = sqlite3_value_text(argv[1]);

   if( zPattern==0 || zPattern[0]==0 ) return;

   nPattern = sqlite3_value_bytes(argv[1]);

   assert( zPattern==sqlite3_value_text(argv[1]) );  /* No encoding change */

   zRep = sqlite3_value_text(argv[2]);

   if( zRep==0 ) return;

   nRep = sqlite3_value_bytes(argv[2]);

   assert( zRep==sqlite3_value_text(argv[2]) );

   nOut = nStr + 1;

   assert( nOut<SQLITE_MAX_LENGTH );

   zOut = contextMalloc(context, (int)nOut);

   if( zOut==0 ){

     return;

   }

   loopLimit = nStr - nPattern;  

   for(i=j=0; i<=loopLimit; i++){

     if( zStr[i]!=zPattern[0] || memcmp(&zStr[i], zPattern, nPattern) ){

       zOut[j++] = zStr[i];

     }else{

       u8 *zOld;

       nOut += nRep - nPattern;

       if( nOut>=SQLITE_MAX_LENGTH ){

         sqlite3_result_error_toobig(context);

         sqlite3_free(zOut);

         return;

       }

       zOld = zOut;

       zOut = sqlite3_realloc(zOut, (int)nOut);