SQLite

** be clear:  this routine converts utf8 to unicode.  This routine is 
** optimized for the common case where the next character is a single byte.
*/
static unsigned re_next_char(ReInput *p){
  unsigned c;
  if( p->i>=p->mx ) return 0;
  c = p->z[p->i++];
  if( c>=0x80 ){
    if( (c&0xe0)==0xc0 && p->i<p->mx && (p->z[p->i]&0xc0)==0x80 ){
      c = (c&0x1f)<<6 | (p->z[p->i++]&0x3f);
      if( c<0x80 ) c = 0xfffd;
    }else if( (c&0xf0)==0xe0 && p->i+1<p->mx && (p->z[p->i]&0xc0)==0x80
           && (p->z[p->i+1]&0xc0)==0x80 ){
      c = (c&0x0f)<<12 | ((p->z[p->i]&0x3f)<<6) | (p->z[p->i+1]&0x3f);
      p->i += 2;
      if( c<=0x3ff || (c>=0xd800 && c<=0xdfff) ) c = 0xfffd;
    }else if( (c&0xf8)==0xf0 && p->i+3<p->mx && (p->z[p->i]&0xc0)==0x80
           && (p->z[p->i+1]&0xc0)==0x80 && (p->z[p->i+2]&0xc0)==0x80 ){
      c = (c&0x07)<<18 | ((p->z[p->i]&0x3f)<<12) | ((p->z[p->i+1]&0x3f)<<6)
                       | (p->z[p->i+2]&0x3f);
      p->i += 3;
      if( c<=0xffff || c>0x10ffff ) c = 0xfffd;
    }else{
      c = 0xfffd;
    }
  }
  return c;
}
static unsigned re_next_char_nocase(ReInput *p){

/* Return true if c is a "digit" character:  [0-9] */
static int re_digit_char(int c){
  return (c>='0' && c<='9');
}

/* Return true if c is a perl "space" character:  [ \t\r\n\v\f] */
static int re_space_char(int c){
  return c==' ' || c=='\t' || c=='\n' || c=='\r' || c=='\v' || c=='\f';
}

/* Run a compiled regular expression on the zero-terminated input
** string zIn[].  Return true on a match and false if there is no match.
*/
int re_match(ReCompiled *pRe, const unsigned char *zIn, int nIn){
  ReStateSet aStateSet[2], *pThis, *pNext;
  ReStateNumber aSpace[100];
  ReStateNumber *pToFree;
  unsigned int i = 0;
  unsigned int iSwap = 0;
  int c = RE_EOF+1;
  int cPrev = 0;
  int rc = 0;
  ReInput in;

  in.z = zIn;
  in.i = 0;
  in.mx = nIn>=0 ? nIn : strlen((char const*)zIn);

  /* Look for the initial prefix match, if there is one. */
  if( pRe->nInit ){
    unsigned char x = pRe->zInit[0];
    while( in.i+pRe->nInit<=in.mx 
        && (zIn[in.i]!=x || memcmp(zIn+in.i, pRe->zInit, pRe->nInit)!=0)
    ){
      in.i++;
    }
    if( in.i+pRe->nInit>in.mx ) return 0;
  }

  if( pRe->nState<=(sizeof(aSpace)/(sizeof(aSpace[0])*2)) ){
    pToFree = 0;
    aStateSet[0].aState = aSpace;
  }else{
    pToFree = sqlite3_malloc( sizeof(ReStateNumber)*2*pRe->nState );
    if( pToFree==0 ) return -1;
    aStateSet[0].aState = pToFree;

  if( zIn[0]=='^' ){
    zIn++;
  }else{
    re_append(pRe, RE_OP_ANYSTAR, 0);
  }
  pRe->sIn.z = (unsigned char*)zIn;
  pRe->sIn.i = 0;
  pRe->sIn.mx = strlen(zIn);
  zErr = re_subcompile_re(pRe);
  if( zErr ){
    re_free(pRe);
    return zErr;
  }
  if( rePeek(pRe)=='$' && pRe->sIn.i+1>=pRe->sIn.mx ){
    re_append(pRe, RE_OP_MATCH, RE_EOF);
    re_append(pRe, RE_OP_ACCEPT, 0);
    *ppRe = pRe;
  }else if( pRe->sIn.i>=pRe->sIn.mx ){
    re_append(pRe, RE_OP_ACCEPT, 0);
    *ppRe = pRe;
  }else{
    re_free(pRe);
    return "unrecognized character";
  }

  /* The following is a performance optimization.  If the regex begins with
  ** ".*" (if the input regex lacks an initial "^") and afterwards there are
  ** one or more matching characters, enter those matching characters into
  ** zInit[].  The re_match() routine can then search ahead in the input 
  ** string looking for the initial match without having to run the whole
  ** regex engine over the string.  Do not worry able trying to match
  ** unicode characters beyond plane 0 - those are very rare and this is
  ** just an optimization. */
  if( pRe->aOp[0]==RE_OP_ANYSTAR ){
    for(j=0, i=1; j<sizeof(pRe->zInit)-2 && pRe->aOp[i]==RE_OP_MATCH; i++){
      unsigned x = pRe->aArg[i];
      if( x<=127 ){
        pRe->zInit[j++] = x;
      }else if( x<=0xfff ){
        pRe->zInit[j++] = 0xc0 | (x>>6);
        pRe->zInit[j++] = 0x80 | (x&0x3f);
      }else if( x<=0xffff ){
        pRe->zInit[j++] = 0xd0 | (x>>12);
        pRe->zInit[j++] = 0x80 | ((x>>6)&0x3f);
        pRe->zInit[j++] = 0x80 | (x&0x3f);
      }else{
        break;
      }
    }
    if( j>0 && pRe->zInit[j-1]==0 ) j--;
    pRe->nInit = j;
  }