SQLite

  $(TOP)/ext/fts5/fts5_test_mi.c \
  $(TOP)/ext/fts5/fts5_test_tok.c \
  $(TOP)/ext/misc/ieee754.c \
  $(TOP)/ext/misc/mmapwarm.c \
  $(TOP)/ext/misc/nextchar.c \
  $(TOP)/ext/misc/normalize.c \
  $(TOP)/ext/misc/percentile.c \
  $(TOP)/ext/misc/prefixes.c \
  $(TOP)/ext/misc/regexp.c \
  $(TOP)/ext/misc/remember.c \
  $(TOP)/ext/misc/series.c \
  $(TOP)/ext/misc/spellfix.c \
  $(TOP)/ext/misc/totype.c \
  $(TOP)/ext/misc/unionvtab.c \
  $(TOP)/ext/misc/wholenumber.c \

  $(TOP)\ext\fts5\fts5_test_mi.c \
  $(TOP)\ext\fts5\fts5_test_tok.c \
  $(TOP)\ext\misc\ieee754.c \
  $(TOP)\ext\misc\mmapwarm.c \
  $(TOP)\ext\misc\nextchar.c \
  $(TOP)\ext\misc\normalize.c \
  $(TOP)\ext\misc\percentile.c \
  $(TOP)\ext\misc\prefixes.c \
  $(TOP)\ext\misc\regexp.c \
  $(TOP)\ext\misc\remember.c \
  $(TOP)\ext\misc\series.c \
  $(TOP)\ext\misc\spellfix.c \
  $(TOP)\ext\misc\totype.c \
  $(TOP)\ext\misc\unionvtab.c \
  $(TOP)\ext\misc\wholenumber.c

  /* xRename     */ 0,
  /* xSavepoint  */ 0,
  /* xRelease    */ 0,
  /* xRollbackTo */ 0,
  /* xShadowName */ 0
};

/*
** This is a copy of the SQLITE_SKIP_UTF8(zIn) macro in sqliteInt.h.
**
** Assuming zIn points to the first byte of a UTF-8 character,
** advance zIn to point to the first byte of the next UTF-8 character.
*/
#define PREFIX_SKIP_UTF8(zIn) {                        \
  if( (*(zIn++))>=0xc0 ){                              \
    while( (*zIn & 0xc0)==0x80 ){ zIn++; }             \
  }                                                    \
}

/*
** Implementation of function prefix_length(). This function accepts two
** strings as arguments and returns the length in characters (not bytes), 
** of the longest prefix shared by the two strings. For example:
**
**   prefix_length('abcdxxx', 'abcyy') == 3
**   prefix_length('abcdxxx', 'bcyyy') == 0
**   prefix_length('abcdxxx', 'ab')    == 2
**   prefix_length('ab',      'abcd')  == 2
**
** This function assumes the input is well-formed utf-8. If it is not,
** it is possible for this function to return -1.
*/
static void prefixLengthFunc(
  sqlite3_context *ctx,
  int nVal,
  sqlite3_value **apVal
){
  int nByte;                      /* Number of bytes to compare */
  int nRet = 0;                   /* Return value */
  const unsigned char *zL = sqlite3_value_text(apVal[0]);
  const unsigned char *zR = sqlite3_value_text(apVal[1]);
  int nL = sqlite3_value_bytes(apVal[0]);
  int nR = sqlite3_value_bytes(apVal[1]);
  int i;

  nByte = (nL > nR ? nL : nR);
  for(i=0; i<nByte; i++){
    if( zL[i]!=zR[i] ) break;
    if( (zL[i] & 0xC0)!=0x80 ) nRet++;
  }

  if( (zL[i] & 0xC0)==0x80 ) nRet--;
  sqlite3_result_int(ctx, nRet);
}

#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);
  if( rc==SQLITE_OK ){
    rc = sqlite3_create_function(
        db, "prefix_length", 2, SQLITE_UTF8, 0, prefixLengthFunc, 0, 0
    );
  }
  return rc;
}

  $(TOP)/ext/misc/fileio.c \
  $(TOP)/ext/misc/fuzzer.c \
  $(TOP)/ext/misc/ieee754.c \
  $(TOP)/ext/misc/mmapwarm.c \
  $(TOP)/ext/misc/nextchar.c \
  $(TOP)/ext/misc/normalize.c \
  $(TOP)/ext/misc/percentile.c \
  $(TOP)/ext/misc/prefixes.c \
  $(TOP)/ext/misc/regexp.c \
  $(TOP)/ext/misc/remember.c \
  $(TOP)/ext/misc/series.c \
  $(TOP)/ext/misc/spellfix.c \
  $(TOP)/ext/misc/totype.c \
  $(TOP)/ext/misc/unionvtab.c \
  $(TOP)/ext/misc/wholenumber.c \

  extern int sqlite3_eval_init(sqlite3*,char**,const sqlite3_api_routines*);
  extern int sqlite3_explain_init(sqlite3*,char**,const sqlite3_api_routines*);
  extern int sqlite3_fileio_init(sqlite3*,char**,const sqlite3_api_routines*);
  extern int sqlite3_fuzzer_init(sqlite3*,char**,const sqlite3_api_routines*);
  extern int sqlite3_ieee_init(sqlite3*,char**,const sqlite3_api_routines*);
  extern int sqlite3_nextchar_init(sqlite3*,char**,const sqlite3_api_routines*);
  extern int sqlite3_percentile_init(sqlite3*,char**,const sqlite3_api_routines*);
  extern int sqlite3_prefixes_init(sqlite3*,char**,const sqlite3_api_routines*);
  extern int sqlite3_regexp_init(sqlite3*,char**,const sqlite3_api_routines*);
  extern int sqlite3_remember_init(sqlite3*,char**,const sqlite3_api_routines*);
  extern int sqlite3_series_init(sqlite3*,char**,const sqlite3_api_routines*);
  extern int sqlite3_spellfix_init(sqlite3*,char**,const sqlite3_api_routines*);
  extern int sqlite3_totype_init(sqlite3*,char**,const sqlite3_api_routines*);
  extern int sqlite3_wholenumber_init(sqlite3*,char**,const sqlite3_api_routines*);
  extern int sqlite3_unionvtab_init(sqlite3*,char**,const sqlite3_api_routines*);

    { "eval",                  sqlite3_eval_init                 },
    { "explain",               sqlite3_explain_init              },
    { "fileio",                sqlite3_fileio_init               },
    { "fuzzer",                sqlite3_fuzzer_init               },
    { "ieee754",               sqlite3_ieee_init                 },
    { "nextchar",              sqlite3_nextchar_init             },
    { "percentile",            sqlite3_percentile_init           },
    { "prefixes",              sqlite3_prefixes_init             },
    { "regexp",                sqlite3_regexp_init               },
    { "remember",              sqlite3_remember_init             },
    { "series",                sqlite3_series_init               },
    { "spellfix",              sqlite3_spellfix_init             },
    { "totype",                sqlite3_totype_init               },
    { "unionvtab",             sqlite3_unionvtab_init            },
    { "wholenumber",           sqlite3_wholenumber_init          },

# 2018-01-15
#
# 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 regression tests for SQLite library.  The
# focus of this file is prefixes.c extension
#

set testdir [file dirname $argv0]
source $testdir/tester.tcl
set testprefix unionvtab

ifcapable !vtab {
  finish_test
  return
}

load_static_extension db prefixes

foreach {tn zLeft zRight expected} {
  1 abcdxxx abcyy    3
  2 abcdxxx bcyyy    0
  3 abcdxxx ab       2
  4 ab      abcd     2

  5 "xyz\u1234xz" "xyz\u1234xy" 5
  6 "xyz\u1234"   "xyz\u1234xy" 4
  7 "xyz\u1234"   "xyz\u1234"   4
  8 "xyz\u1234xy" "xyz\u1234"   4
  9 "xyz\u1234xy" "xyz\u1233"   3
 10 "xyz\u1234xy" "xyz\u1235"   3
} {
  do_execsql_test 1.$tn { SELECT prefix_length($zLeft, $zRight) } $expected
}


do_execsql_test 2.0 {
  CREATE TABLE t1(k TEXT UNIQUE, v INTEGER);
  INSERT INTO t1 VALUES
    ('aback', 1),
    ('abaft', 2),
    ('abandon', 3),
    ('abandoned', 4),
    ('abandoning', 5),
    ('abandonment', 6),
    ('abandons', 7),
    ('abase', 8),
    ('abased', 9),
    ('abasement', 10),
    ('abasements', 11),
    ('abases', 12),
    ('abash', 13),
    ('abashed', 14),
    ('abashes', 15),
    ('abashing', 16),
    ('abasing', 17),
    ('abate', 18),
    ('abated', 19),
    ('abatement', 20),
    ('abatements', 21);
}

foreach {tn INPUT expected} {
  1 abatementt   abatement
  2 abashet      abash
  3 abandonio    abandon
  4 abasemenu    abase
} {
  do_execsql_test 2.$tn {
    WITH finder(str) AS (
      SELECT (SELECT max(k) FROM t1 WHERE k<=$INPUT)
        UNION ALL
        SELECT (
          SELECT max(k) FROM t1 
          WHERE k<=substr($INPUT, 1, prefix_length(finder.str, $INPUT))
        ) FROM finder WHERE length(finder.str)>0
      )
    SELECT str FROM finder WHERE length(str)==prefix_length(str, $INPUT) LIMIT 1
  } $expected
}

finish_test