Add the "prefixes" table-valued function in the ext/misc folder.

FossilOrigin-Name: f0fd2163fc23a555ef03af43294a14fcabae6921f52e64c979286c745b4f6218

ext/misc/prefixes.c

@@ -0,0 +1,265 @@
+/*
+** 2018-04-19
+**
+** 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 implements a table-valued function:
+**
+**      prefixes('abcdefg')
+**
+** The function has a single (non-HIDDEN) column named prefix that takes
+** on all prefixes of the string in its argument, including an empty string
+** and the input string itself.  The order of prefixes is from longest
+** to shortest.
+*/
+#if !defined(SQLITEINT_H)
+#include "sqlite3ext.h"
+#endif
+SQLITE_EXTENSION_INIT1
+#include <string.h>
+#include <assert.h>
+
+/* prefixes_vtab is a subclass of sqlite3_vtab which is
+** underlying representation of the virtual table
+*/
+typedef struct prefixes_vtab prefixes_vtab;
+struct prefixes_vtab {
+  sqlite3_vtab base;  /* Base class - must be first */
+  /* No additional fields are necessary */
+};
+
+/* prefixes_cursor is a subclass of sqlite3_vtab_cursor which will
+** serve as the underlying representation of a cursor that scans
+** over rows of the result
+*/
+typedef struct prefixes_cursor prefixes_cursor;
+struct prefixes_cursor {
+  sqlite3_vtab_cursor base;  /* Base class - must be first */
+  sqlite3_int64 iRowid;      /* The rowid */
+  char *zStr;                /* Original string to be prefixed */
+  int nStr;                  /* Length of the string in bytes */
+};
+
+/*
+** The prefixesConnect() method is invoked to create a new
+** template virtual table.
+**
+** Think of this routine as the constructor for prefixes_vtab objects.
+**
+** All this routine needs to do is:
+**
+**    (1) Allocate the prefixes_vtab object and initialize all fields.
+**
+**    (2) Tell SQLite (via the sqlite3_declare_vtab() interface) what the
+**        result set of queries against the virtual table will look like.
+*/
+static int prefixesConnect(
+  sqlite3 *db,
+  void *pAux,
+  int argc, const char *const*argv,
+  sqlite3_vtab **ppVtab,
+  char **pzErr
+){
+  prefixes_vtab *pNew;
+  int rc;
+
+  rc = sqlite3_declare_vtab(db,
+           "CREATE TABLE prefixes(prefix TEXT, original_string TEXT HIDDEN)"
+       );
+  if( rc==SQLITE_OK ){
+    pNew = sqlite3_malloc( sizeof(*pNew) );
+    *ppVtab = (sqlite3_vtab*)pNew;
+    if( pNew==0 ) return SQLITE_NOMEM;
+    memset(pNew, 0, sizeof(*pNew));
+  }
+  return rc;
+}
+
+/*
+** This method is the destructor for prefixes_vtab objects.
+*/
+static int prefixesDisconnect(sqlite3_vtab *pVtab){
+  prefixes_vtab *p = (prefixes_vtab*)pVtab;
+  sqlite3_free(p);
+  return SQLITE_OK;
+}
+
+/*
+** Constructor for a new prefixes_cursor object.
+*/
+static int prefixesOpen(sqlite3_vtab *p, sqlite3_vtab_cursor **ppCursor){
+  prefixes_cursor *pCur;
+  pCur = sqlite3_malloc( sizeof(*pCur) );
+  if( pCur==0 ) return SQLITE_NOMEM;
+  memset(pCur, 0, sizeof(*pCur));
+  *ppCursor = &pCur->base;
+  return SQLITE_OK;
+}
+
+/*
+** Destructor for a prefixes_cursor.
+*/
+static int prefixesClose(sqlite3_vtab_cursor *cur){
+  prefixes_cursor *pCur = (prefixes_cursor*)cur;
+  sqlite3_free(pCur->zStr);
+  sqlite3_free(pCur);
+  return SQLITE_OK;
+}
+
+
+/*
+** Advance a prefixes_cursor to its next row of output.
+*/
+static int prefixesNext(sqlite3_vtab_cursor *cur){
+  prefixes_cursor *pCur = (prefixes_cursor*)cur;
+  pCur->iRowid++;
+  return SQLITE_OK;
+}
+
+/*
+** Return values of columns for the row at which the prefixes_cursor
+** is currently pointing.
+*/
+static int prefixesColumn(
+  sqlite3_vtab_cursor *cur,   /* The cursor */
+  sqlite3_context *ctx,       /* First argument to sqlite3_result_...() */
+  int i                       /* Which column to return */
+){
+  prefixes_cursor *pCur = (prefixes_cursor*)cur;
+  switch( i ){
+    case 0:
+      sqlite3_result_text(ctx, pCur->zStr, pCur->nStr - (int)pCur->iRowid,
+                          0); 
+      break;
+    default:
+      sqlite3_result_text(ctx, pCur->zStr, pCur->nStr, 0);
+      break;
+  }
+  return SQLITE_OK;
+}
+
+/*
+** Return the rowid for the current row.  In this implementation, the
+** rowid is the same as the output value.
+*/
+static int prefixesRowid(sqlite3_vtab_cursor *cur, sqlite_int64 *pRowid){
+  prefixes_cursor *pCur = (prefixes_cursor*)cur;
+  *pRowid = pCur->iRowid;
+  return SQLITE_OK;
+}
+
+/*
+** Return TRUE if the cursor has been moved off of the last
+** row of output.
+*/
+static int prefixesEof(sqlite3_vtab_cursor *cur){
+  prefixes_cursor *pCur = (prefixes_cursor*)cur;
+  return pCur->iRowid>pCur->nStr;
+}
+
+/*
+** This method is called to "rewind" the prefixes_cursor object back
+** to the first row of output.  This method is always called at least
+** once prior to any call to prefixesColumn() or prefixesRowid() or 
+** prefixesEof().
+*/
+static int prefixesFilter(
+  sqlite3_vtab_cursor *pVtabCursor, 
+  int idxNum, const char *idxStr,
+  int argc, sqlite3_value **argv
+){
+  prefixes_cursor *pCur = (prefixes_cursor *)pVtabCursor;
+  sqlite3_free(pCur->zStr);
+  if( argc>0 ){
+    pCur->zStr = sqlite3_mprintf("%s", sqlite3_value_text(argv[0]));
+    pCur->nStr = pCur->zStr ? (int)strlen(pCur->zStr) : 0;
+  }else{
+    pCur->zStr = 0;
+    pCur->nStr = 0;
+  }
+  pCur->iRowid = 0;
+  return SQLITE_OK;
+}
+
+/*
+** SQLite will invoke this method one or more times while planning a query
+** that uses the virtual table.  This routine needs to create
+** a query plan for each invocation and compute an estimated cost for that
+** plan.
+*/
+static int prefixesBestIndex(
+  sqlite3_vtab *tab,
+  sqlite3_index_info *pIdxInfo
+){
+  /* Search for a usable equality constraint against column 1 
+  ** (original_string) and use it if at all possible */
+  int i;
+  const struct sqlite3_index_constraint *p;
+
+  for(i=0, p=pIdxInfo->aConstraint; i<pIdxInfo->nConstraint; i++, p++){
+    if( p->iColumn!=1 ) continue;
+    if( p->op!=SQLITE_INDEX_CONSTRAINT_EQ ) continue;
+    if( !p->usable ) continue;
+    pIdxInfo->aConstraintUsage[i].argvIndex = 1;
+    pIdxInfo->aConstraintUsage[i].omit = 1;
+    pIdxInfo->estimatedCost = (double)10;
+    pIdxInfo->estimatedRows = 10;
+    return SQLITE_OK;
+  }
+  pIdxInfo->estimatedCost = (double)1000000000;
+  pIdxInfo->estimatedRows = 1000000000;
+  return SQLITE_OK;
+}
+
+/*
+** This following structure defines all the methods for the 
+** virtual table.
+*/
+static sqlite3_module prefixesModule = {
+  /* iVersion    */ 0,
+  /* xCreate     */ 0,
+  /* xConnect    */ prefixesConnect,
+  /* xBestIndex  */ prefixesBestIndex,
+  /* xDisconnect */ prefixesDisconnect,
+  /* xDestroy    */ 0,
+  /* xOpen       */ prefixesOpen,
+  /* xClose      */ prefixesClose,
+  /* xFilter     */ prefixesFilter,
+  /* xNext       */ prefixesNext,
+  /* xEof        */ prefixesEof,
+  /* xColumn     */ prefixesColumn,
+  /* xRowid      */ prefixesRowid,
+  /* xUpdate     */ 0,
+  /* xBegin      */ 0,
+  /* xSync       */ 0,
+  /* xCommit     */ 0,
+  /* xRollback   */ 0,
+  /* xFindMethod */ 0,
+  /* xRename     */ 0,
+  /* xSavepoint  */ 0,
+  /* xRelease    */ 0,
+  /* xRollbackTo */ 0,
+  /* xShadowName */ 0
+};
+
+
+#ifdef _WIN32
+__declspec(dllexport)
+#endif
+int sqlite3_prefixes_init(
+  sqlite3 *db, 
+  char **pzErrMsg, 
+  const sqlite3_api_routines *pApi
+){
+  int rc = SQLITE_OK;
+  SQLITE_EXTENSION_INIT2(pApi);
+  rc = sqlite3_create_module(db, "prefixes", &prefixesModule, 0);
+  return rc;
+}

manifest

@@ -1,5 +1,5 @@
-C Fix\sa\sproblem\scausing\sa\scrash\sif\san\sfts5vocab\stable\swas\screated\sto\squery\san\nfts3/4\sFTS\sindex.
-D 2019-01-14T15:35:15.573
+C Add\sthe\s"prefixes"\stable-valued\sfunction\sin\sthe\sext/misc\sfolder.
+D 2019-01-14T16:16:30.437
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F Makefile.in 45a3fef4d325ac0220c2172aeec4e4321da351f073f3b8e8ddea655f49ef6f2b
@@ -295,6 +295,7 @@ F ext/misc/mmapwarm.c 8c5fe90d807a23e44a8b93e96e8b812b19b300d5fd8c1d40a4fd1d8224
 F ext/misc/nextchar.c 279f80fe8ef5ba413242e2704e246503ac601f005eefb180d19e6c920338a0ba
 F ext/misc/normalize.c b4290464f542bae7a97b43f15bd197949b833ffd668b7c313631bd5d4610212c
 F ext/misc/percentile.c a6a1594c104da2d0ceab38fe609eb2f65529272377827f6f8a2b5c9fa6119e7e
+F ext/misc/prefixes.c ac95cf723927b9e4b6f2b45eec743986259e3c2618f92ffa9fd780e13c75f70e
 F ext/misc/regexp.c 79345bf03496155a640ee0300d3307296761cebb5e115b4e342cc2fb5861ec10
 F ext/misc/remember.c add730f0f7e7436cd15ea3fd6a90fd83c3f706ab44169f7f048438b7d6baa69c
 F ext/misc/rot13.c 540a169cb0d74f15522a8930b0cccdcb37a4fd071d219a5a083a319fc6e8db77
@@ -1798,7 +1799,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
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+R e9e76e5c2ca649c80198f4ce0b8026d6
+U drh
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manifest.uuid

@@ -1 +1 @@
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