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Overview
Comment:More simplification of the sqlite3AtoF() routine. Add special comments to indicate branches that are for optimization purposes only and that give the correct answer even if always or never taken.
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SHA1:0065fe97cb8e5076acae1bf1560fd2f69dab9014
User & Date: drh 2016-04-27 15:24:13
Context
2016-04-28
00:32
Change the sqlite3Atoi64() routine so that it returns failure if not all of the input characters are consumed, even if it consumed all characters up to the first 0x00. This has no impact on external APIs as far as I can tell. check-in: 46d4ffff user: drh tags: trunk
2016-04-27
18:54
Modify the permutations.test script so as to set any permutation specific configuration values before running each individual test script. check-in: 2662d8fe user: dan tags: permutations-fix
15:24
More simplification of the sqlite3AtoF() routine. Add special comments to indicate branches that are for optimization purposes only and that give the correct answer even if always or never taken. check-in: 0065fe97 user: drh tags: trunk
02:35
Remove still more unnecessary branches from sqlite3AtoF(). check-in: 3adfe9f3 user: drh tags: trunk
Changes
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Changes to src/util.c.

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  i64 s = 0;       /* significand */
  int d = 0;       /* adjust exponent for shifting decimal point */
  int esign = 1;   /* sign of exponent */
  int e = 0;       /* exponent */
  int eValid = 1;  /* True exponent is either not used or is well-formed */
  double result;
  int nDigits = 0;
  int nonNum = 0;

  assert( enc==SQLITE_UTF8 || enc==SQLITE_UTF16LE || enc==SQLITE_UTF16BE );
  *pResult = 0.0;   /* Default return value, in case of an error */

  if( enc==SQLITE_UTF8 ){
    incr = 1;
  }else{
    int i;
    incr = 2;
    assert( SQLITE_UTF16LE==2 && SQLITE_UTF16BE==3 );
    for(i=3-enc; i<length && z[i]==0; i+=2){}
    nonNum = i<length;
    zEnd = z+i+enc-3;
    z += (enc&1);
  }

  /* skip leading spaces */
  while( z<zEnd && sqlite3Isspace(*z) ) z+=incr;
  if( z>=zEnd ) return 0;

................................................................................
  }
  if( z>=zEnd ) goto do_atof_calc;

  /* if exponent is present */
  if( *z=='e' || *z=='E' ){
    z+=incr;
    eValid = 0;




    if( z>=zEnd ) goto do_atof_calc;

    /* get sign of exponent */
    if( *z=='-' ){
      esign = -1;
      z+=incr;
    }else if( *z=='+' ){
      z+=incr;
    }
................................................................................
  if( e<0 ) {
    esign = -1;
    e *= -1;
  } else {
    esign = 1;
  }

  /* if 0 significand */
  if( !s ) {
    /* In the IEEE 754 standard, zero is signed.
    ** Add the sign if we've seen at least one digit */
    result = sign<0 ? -(double)0 : (double)0;
  } else {
    /* attempt to reduce exponent */






    if( esign>0 ){
      while( s<(LARGEST_INT64/10) && e>0 ) e--,s*=10;


    }else{
      while( !(s%10) && e>0 ) e--,s/=10;




    }

    /* adjust the sign of significand */
    s = sign<0 ? -s : s;

    /* if exponent, scale significand as appropriate
    ** and store in result. */
    if( e ){
      LONGDOUBLE_TYPE scale = 1.0;
      /* attempt to handle extremely small/large numbers better */
      if( e>307 && e<342 ){

        while( e%308 ) { scale *= 1.0e+1; e -= 1; }
        if( esign<0 ){
          result = s / scale;
          result /= 1.0e+308;
        }else{
          result = s * scale;
          result *= 1.0e+308;
        }
      }else if( e>=342 ){
        if( esign<0 ){
          result = 0.0*s;
        }else{
          result = 1e308*1e308*s;  /* Infinity */

        }
      }else{
        /* 1.0e+22 is the largest power of 10 than can be 
        ** represented exactly. */
        while( e%22 ) { scale *= 1.0e+1; e -= 1; }
        while( e>0 ) { scale *= 1.0e+22; e -= 22; }
        if( esign<0 ){
          result = s / scale;
        }else{
          result = s * scale;
        }
      }
    } else {
      result = (double)s;
    }
  }

  /* store the result */
  *pResult = result;

  /* return true if number and no extra non-whitespace chracters after */
  return z>=zEnd && nDigits>0 && eValid && nonNum==0;
#else
  return !sqlite3Atoi64(z, pResult, length, enc);
#endif /* SQLITE_OMIT_FLOATING_POINT */
}

/*
** Compare the 19-character string zNum against the text representation







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  i64 s = 0;       /* significand */
  int d = 0;       /* adjust exponent for shifting decimal point */
  int esign = 1;   /* sign of exponent */
  int e = 0;       /* exponent */
  int eValid = 1;  /* True exponent is either not used or is well-formed */
  double result;
  int nDigits = 0;
  int nonNum = 0;  /* True if input contains UTF16 with high byte non-zero */

  assert( enc==SQLITE_UTF8 || enc==SQLITE_UTF16LE || enc==SQLITE_UTF16BE );
  *pResult = 0.0;   /* Default return value, in case of an error */

  if( enc==SQLITE_UTF8 ){
    incr = 1;
  }else{
    int i;
    incr = 2;
    assert( SQLITE_UTF16LE==2 && SQLITE_UTF16BE==3 );
    for(i=3-enc; i<length && z[i]==0; i+=2){}
    nonNum = i<length;
    zEnd = &z[i^1];
    z += (enc&1);
  }

  /* skip leading spaces */
  while( z<zEnd && sqlite3Isspace(*z) ) z+=incr;
  if( z>=zEnd ) return 0;

................................................................................
  }
  if( z>=zEnd ) goto do_atof_calc;

  /* if exponent is present */
  if( *z=='e' || *z=='E' ){
    z+=incr;
    eValid = 0;

    /* This branch is needed to avoid a (harmless) buffer overread.  The 
    ** special comment alerts the mutation tester that the correct answer
    ** is obtained even if the branch is omitted */
    if( z>=zEnd ) goto do_atof_calc;              /*PREVENTS-HARMLESS-OVERREAD*/

    /* get sign of exponent */
    if( *z=='-' ){
      esign = -1;
      z+=incr;
    }else if( *z=='+' ){
      z+=incr;
    }
................................................................................
  if( e<0 ) {
    esign = -1;
    e *= -1;
  } else {
    esign = 1;
  }


  if( s==0 ) {
    /* In the IEEE 754 standard, zero is signed. */

    result = sign<0 ? -(double)0 : (double)0;
  } else {
    /* Attempt to reduce exponent.
    **
    ** Branches that are not required for the correct answer but which only
    ** help to obtain the correct answer faster are marked with special
    ** comments, as a hint to the mutation tester.
    */
    while( e>0 ){                                       /*OPTIMIZATION-IF-TRUE*/
      if( esign>0 ){

        if( s>=(LARGEST_INT64/10) ) break;             /*OPTIMIZATION-IF-FALSE*/
        s *= 10;
      }else{

        if( s%10!=0 ) break;                           /*OPTIMIZATION-IF-FALSE*/
        s /= 10;
      }
      e--;
    }

    /* adjust the sign of significand */
    s = sign<0 ? -s : s;

    if( e==0 ){                                         /*OPTIMIZATION-IF-TRUE*/
      result = (double)s;
    }else{
      LONGDOUBLE_TYPE scale = 1.0;
      /* attempt to handle extremely small/large numbers better */
      if( e>307 ){                                      /*OPTIMIZATION-IF-TRUE*/
        if( e<342 ){                                    /*OPTIMIZATION-IF-TRUE*/
          while( e%308 ) { scale *= 1.0e+1; e -= 1; }
          if( esign<0 ){
            result = s / scale;
            result /= 1.0e+308;
          }else{
            result = s * scale;
            result *= 1.0e+308;
          }
        }else{ assert( e>=342 );
          if( esign<0 ){
            result = 0.0*s;
          }else{
            result = 1e308*1e308*s;  /* Infinity */
          }
        }
      }else{
        /* 1.0e+22 is the largest power of 10 than can be 
        ** represented exactly. */
        while( e%22 ) { scale *= 1.0e+1; e -= 1; }
        while( e>0 ) { scale *= 1.0e+22; e -= 22; }
        if( esign<0 ){
          result = s / scale;
        }else{
          result = s * scale;
        }
      }


    }
  }

  /* store the result */
  *pResult = result;

  /* return true if number and no extra non-whitespace chracters after */
  return z==zEnd && nDigits>0 && eValid && nonNum==0;
#else
  return !sqlite3Atoi64(z, pResult, length, enc);
#endif /* SQLITE_OMIT_FLOATING_POINT */
}

/*
** Compare the 19-character string zNum against the text representation