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-rw-r--r--ext/misc/nextchar.c265
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diff --git a/ext/misc/nextchar.c b/ext/misc/nextchar.c
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+/*
+** 2013-02-28
+**
+** 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 code to implement the next_char(A,T,F,W) SQL function.
+**
+** The next_char(A,T,F,H) function finds all valid "next" characters for
+** string A given the vocabulary in T.F. The T.F field should be indexed.
+** If the W value exists and is a non-empty string, then it is an SQL
+** expression that limits the entries in T.F that will be considered.
+**
+** For example, suppose an application has a dictionary like this:
+**
+** CREATE TABLE dictionary(word TEXT UNIQUE);
+**
+** Further suppose that for user keypad entry, it is desired to disable
+** (gray out) keys that are not valid as the next character. If the
+** the user has previously entered (say) 'cha' then to find all allowed
+** next characters (and thereby determine when keys should not be grayed
+** out) run the following query:
+**
+** SELECT next_char('cha','dictionary','word');
+*/
+#include "sqlite3ext.h"
+SQLITE_EXTENSION_INIT1
+#include <string.h>
+
+/*
+** A structure to hold context of the next_char() computation across
+** nested function calls.
+*/
+typedef struct nextCharContext nextCharContext;
+struct nextCharContext {
+ sqlite3 *db; /* Database connection */
+ sqlite3_stmt *pStmt; /* Prepared statement used to query */
+ const unsigned char *zPrefix; /* Prefix to scan */
+ int nPrefix; /* Size of zPrefix in bytes */
+ int nAlloc; /* Space allocated to aResult */
+ int nUsed; /* Space used in aResult */
+ unsigned int *aResult; /* Array of next characters */
+ int mallocFailed; /* True if malloc fails */
+ int otherError; /* True for any other failure */
+};
+
+/*
+** Append a result character if the character is not already in the
+** result.
+*/
+static void nextCharAppend(nextCharContext *p, unsigned c){
+ int i;
+ for(i=0; i<p->nUsed; i++){
+ if( p->aResult[i]==c ) return;
+ }
+ if( p->nUsed+1 > p->nAlloc ){
+ unsigned int *aNew;
+ int n = p->nAlloc*2 + 30;
+ aNew = sqlite3_realloc(p->aResult, n*sizeof(unsigned int));
+ if( aNew==0 ){
+ p->mallocFailed = 1;
+ return;
+ }else{
+ p->aResult = aNew;
+ p->nAlloc = n;
+ }
+ }
+ p->aResult[p->nUsed++] = c;
+}
+
+/*
+** Write a character into z[] as UTF8. Return the number of bytes needed
+** to hold the character
+*/
+static int writeUtf8(unsigned char *z, unsigned c){
+ if( c<0x00080 ){
+ z[0] = (unsigned char)(c&0xff);
+ return 1;
+ }
+ if( c<0x00800 ){
+ z[0] = 0xC0 + (unsigned char)((c>>6)&0x1F);
+ z[1] = 0x80 + (unsigned char)(c & 0x3F);
+ return 2;
+ }
+ if( c<0x10000 ){
+ z[0] = 0xE0 + (unsigned char)((c>>12)&0x0F);
+ z[1] = 0x80 + (unsigned char)((c>>6) & 0x3F);
+ z[2] = 0x80 + (unsigned char)(c & 0x3F);
+ return 3;
+ }
+ z[0] = 0xF0 + (unsigned char)((c>>18) & 0x07);
+ z[1] = 0x80 + (unsigned char)((c>>12) & 0x3F);
+ z[2] = 0x80 + (unsigned char)((c>>6) & 0x3F);
+ z[3] = 0x80 + (unsigned char)(c & 0x3F);
+ return 4;
+}
+
+/*
+** Read a UTF8 character out of z[] and write it into *pOut. Return
+** the number of bytes in z[] that were used to construct the character.
+*/
+static int readUtf8(const unsigned char *z, unsigned *pOut){
+ static const unsigned char validBits[] = {
+ 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
+ 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f,
+ 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17,
+ 0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f,
+ 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
+ 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f,
+ 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
+ 0x00, 0x01, 0x02, 0x03, 0x00, 0x01, 0x00, 0x00,
+ };
+ unsigned c = z[0];
+ if( c<0xc0 ){
+ *pOut = c;
+ return 1;
+ }else{
+ int n = 1;
+ c = validBits[c-0xc0];
+ while( (z[n] & 0xc0)==0x80 ){
+ c = (c<<6) + (0x3f & z[n++]);
+ }
+ if( c<0x80 || (c&0xFFFFF800)==0xD800 || (c&0xFFFFFFFE)==0xFFFE ){
+ c = 0xFFFD;
+ }
+ *pOut = c;
+ return n;
+ }
+}
+
+/*
+** The nextCharContext structure has been set up. Add all "next" characters
+** to the result set.
+*/
+static void findNextChars(nextCharContext *p){
+ unsigned cPrev = 0;
+ unsigned char zPrev[8];
+ int n, rc;
+
+ for(;;){
+ sqlite3_bind_text(p->pStmt, 1, (char*)p->zPrefix, p->nPrefix,
+ SQLITE_STATIC);
+ n = writeUtf8(zPrev, cPrev+1);
+ sqlite3_bind_text(p->pStmt, 2, (char*)zPrev, n, SQLITE_STATIC);
+ rc = sqlite3_step(p->pStmt);
+ if( rc==SQLITE_DONE ){
+ sqlite3_reset(p->pStmt);
+ return;
+ }else if( rc!=SQLITE_ROW ){
+ p->otherError = rc;
+ return;
+ }else{
+ const unsigned char *zOut = sqlite3_column_text(p->pStmt, 0);
+ unsigned cNext;
+ n = readUtf8(zOut+p->nPrefix, &cNext);
+ sqlite3_reset(p->pStmt);
+ nextCharAppend(p, cNext);
+ cPrev = cNext;
+ if( p->mallocFailed ) return;
+ }
+ }
+}
+
+
+/*
+** next_character(A,T,F,W)
+**
+** Return a string composted of all next possible characters after
+** A for elements of T.F. If W is supplied, then it is an SQL expression
+** that limits the elements in T.F that are considered.
+*/
+static void nextCharFunc(
+ sqlite3_context *context,
+ int argc,
+ sqlite3_value **argv
+){
+ nextCharContext c;
+ const unsigned char *zTable = sqlite3_value_text(argv[1]);
+ const unsigned char *zField = sqlite3_value_text(argv[2]);
+ const unsigned char *zWhere;
+ char *zSql;
+ int rc;
+
+ memset(&c, 0, sizeof(c));
+ c.db = sqlite3_context_db_handle(context);
+ c.zPrefix = sqlite3_value_text(argv[0]);
+ c.nPrefix = sqlite3_value_bytes(argv[0]);
+ if( zTable==0 || zField==0 || c.zPrefix==0 ) return;
+ if( argc<4
+ || (zWhere = sqlite3_value_text(argv[3]))==0
+ || zWhere[0]==0
+ ){
+ zSql = sqlite3_mprintf(
+ "SELECT \"%w\" FROM \"%w\""
+ " WHERE \"%w\">=(?1 || ?2)"
+ " AND \"%w\"<=(?1 || char(1114111))" /* 1114111 == 0x10ffff */
+ " ORDER BY 1 ASC LIMIT 1",
+ zField, zTable, zField, zField);
+ }else{
+ zSql = sqlite3_mprintf(
+ "SELECT \"%w\" FROM \"%w\""
+ " WHERE \"%w\">=(?1 || ?2)"
+ " AND \"%w\"<=(?1 || char(1114111))" /* 1114111 == 0x10ffff */
+ " AND (%s)"
+ " ORDER BY 1 ASC LIMIT 1",
+ zField, zTable, zField, zField, zWhere);
+ }
+ if( zSql==0 ){
+ sqlite3_result_error_nomem(context);
+ return;
+ }
+
+ rc = sqlite3_prepare_v2(c.db, zSql, -1, &c.pStmt, 0);
+ sqlite3_free(zSql);
+ if( rc ){
+ sqlite3_result_error(context, sqlite3_errmsg(c.db), -1);
+ return;
+ }
+ findNextChars(&c);
+ if( c.mallocFailed ){
+ sqlite3_result_error_nomem(context);
+ }else{
+ unsigned char *pRes;
+ pRes = sqlite3_malloc( c.nUsed*4 + 1 );
+ if( pRes==0 ){
+ sqlite3_result_error_nomem(context);
+ }else{
+ int i;
+ int n = 0;
+ for(i=0; i<c.nUsed; i++){
+ n += writeUtf8(pRes+n, c.aResult[i]);
+ }
+ pRes[n] = 0;
+ sqlite3_result_text(context, (const char*)pRes, n, sqlite3_free);
+ }
+ }
+ sqlite3_finalize(c.pStmt);
+ sqlite3_free(c.aResult);
+}
+
+#ifdef _WIN32
+__declspec(dllexport)
+#endif
+int sqlite3_nextchar_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, "next_char", 3, SQLITE_UTF8, 0,
+ nextCharFunc, 0, 0);
+ if( rc==SQLITE_OK ){
+ rc = sqlite3_create_function(db, "next_char", 4, SQLITE_UTF8, 0,
+ nextCharFunc, 0, 0);
+ }
+ return rc;
+}
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