Artifact cf929a63c3db5d893c24c89377871cb89ede44e2:

• File src/encode.c — part of check-in [57f7c597] at 2002-04-25 11:45:42 on branch trunk — Added the "encode.c" source file that contains two utility subroutines that can be used to encode binary data for use in INSERT and UPDATE statements. This is just an initial checking. The code has not yet been integrated into the library. (CVS 545) (user: drh size: 3855)

/*
** 2002 April 25
**
** 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 helper routines used to translate binary data into
** a null-terminated string (suitable for use in SQLite) and back again.
** These are convenience routines for use by people who want to store binary
** data in an SQLite database.  The code in this file is used by any other
** part of the SQLite library.
**
** $Id: encode.c,v 1.1 2002/04/25 11:45:42 drh Exp $
*/
#include "sqliteInt.h"
#include "encode.h"

/*
** Encode a binary buffer "in" of size n bytes so that it contains
** no instances of characters '\'' or '\000'.  The output is 
** null-terminated and can be used as a string value in an INSERT
** or UPDATE statement.
**
** The result is written into a preallocated output buffer "out".
** "out" must be able to hold at least 2 + (n+255)*3/256 + n bytes.
** In other words, the output will be expanded by as much as 3
** bytes for every 256 bytes of input plus 2 bytes of fixed overhead.
*/
void sqlite_encode_binary(const unsigned char *in, int n, unsigned char *out){
  int i, j, e, m;
  int cnt[256];
  memset(cnt, 0, sizeof(cnt));
  for(i=n-1; i>=0; i--){ cnt[in[i]]++; }
  m = n;
  for(i=1; i<256; i++){
    int sum;
    if( i=='\'' ) continue;
    sum = cnt[i] + cnt[(i+1)&0xff] + cnt[(i+'\'')&0xff];
    if( sum<m ){
      m = sum;
      e = i;
      if( m==0 ) break;
    }
  }
  out[0] = e;
  j = 1;
  for(i=0; i<n; i++){
    int c = (in[i] - e)&0xff;
    if( c==0 ){
      out[j++] = 1;
      out[j++] = 1;
    }else if( c==1 ){
      out[j++] = 1;
      out[j++] = 2;
    }else if( c=='\'' ){
      out[j++] = 1;
      out[j++] = 3;
    }else{
      out[j++] = c;
    }
  }
  out[j++] = 0;
}

/*
** Decode the string "in" into binary data and write it into "out".
** This routine reverses the encoded created by sqlite_encode_binary().
** The output will always be a few bytes less than the input.  The number
** of bytes of output is returned.  If the input is not a well-formed
** encoding, -1 is returned.
**
** The "in" and "out" parameters may point to the same buffer in order
** to decode a string in place.
*/
int sqlite_decode_binary(const unsigned char *in, unsigned char *out){
  int i, c, e;
  e = *(in++);
  i = 0;
  while( (c = *(in++))!=0 ){
    if( c==1 ){
      c = *(in++);
      if( c==1 ){
        c = 0;
      }else if( c==2 ){
        c = 1;
      }else if( c==3 ){
        c = '\'';
      }else{
        return -1;
      }
    }
    out[i++] = (c + e)&0xff;
  }
  return i;
}

#ifdef ENCODER_TEST
/*
** The subroutines above are not tested by the usual test suite.  To test
** these routines, compile just this one file with a -DENCODER_TEST=1 option
** and run the result.
*/
int main(int argc, char **argv){
  int i, j, n, m;
  unsigned char in[20000];
  unsigned char out[30000];

  for(i=0; i<10000; i++){
    printf("Test %d: ", i+1);
    n = rand() % sizeof(in);
    for(j=0; j<n; j++) in[j] = rand() & 0xff;
    sqlite_encode_binary(in, n, out);
    printf("size %d->%d ", n, strlen(out)+1);
    m = 2 + (n+255)*3/256 + n;
    if( strlen(out)+1>m ){
      printf(" ERROR output too big\n");
      exit(1);
    }
    for(j=0; out[j]; j++){
      if( out[j]=='\'' ){
        printf(" ERROR contains (')\n");
        exit(1);
      }
    }
    j = sqlite_decode_binary(out, out);
    if( j!=n ){
      printf(" ERROR decode size %d\n", j);
      exit(1);
    }
    if( memcmp(in, out, n)!=0 ){
      printf(" ERROR decode mismatch\n");
      exit(1);
    }
    printf(" OK\n");
  }
}
#endif /* ENCODER_TEST */