SQLite

**
*************************************************************************
** Utility functions used throughout sqlite.
**
** This file contains functions for allocating memory, comparing
** strings, and stuff like that.
**
** $Id: util.c,v 1.83 2004/05/18 15:57:42 drh Exp $
*/
#include "sqliteInt.h"
#include <stdarg.h>
#include <ctype.h>

/*
** If malloc() ever fails, this global variable gets set to 1.

    a += strlen(&a[1]) + 2;
    b += strlen(&b[1]) + 2;
  }
  if( dir=='-' || dir=='D' ) res = -res;
  return res;
}

/*
** Some powers of 64.  These constants are needed in the
** sqlite3RealToSortable() routine below.
*/
#define _64e3  (64.0 * 64.0 * 64.0)
#define _64e4  (64.0 * 64.0 * 64.0 * 64.0)
#define _64e15 (_64e3 * _64e4 * _64e4 * _64e4)
#define _64e16 (_64e4 * _64e4 * _64e4 * _64e4)
#define _64e63 (_64e15 * _64e16 * _64e16 * _64e16)
#define _64e64 (_64e16 * _64e16 * _64e16 * _64e16)

/*
** The following procedure converts a double-precision floating point
** number into a string.  The resulting string has the property that
** two such strings comparied using strcmp() or memcmp() will give the
** same results as a numeric comparison of the original floating point
** numbers.
**
** This routine is used to generate database keys from floating point
** numbers such that the keys sort in the same order as the original
** floating point numbers even though the keys are compared using
** memcmp().
**
** The calling function should have allocated at least 14 characters
** of space for the buffer z[].
*/
void sqlite3RealToSortable(double r, char *z){
  int neg;
  int exp;
  int cnt = 0;

  /* This array maps integers between 0 and 63 into base-64 digits.
  ** The digits must be chosen such at their ASCII codes are increasing.
  ** This means we can not use the traditional base-64 digit set. */
  static const char zDigit[] = 
     "0123456789"
     "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
     "abcdefghijklmnopqrstuvwxyz"
     "|~";
  if( r<0.0 ){
    neg = 1;
    r = -r;
    *z++ = '-';
  } else {
    neg = 0;
    *z++ = '0';
  }
  exp = 0;

  if( r==0.0 ){
    exp = -1024;
  }else if( r<(0.5/64.0) ){
    while( r < 0.5/_64e64 && exp > -961  ){ r *= _64e64;  exp -= 64; }
    while( r < 0.5/_64e16 && exp > -1009 ){ r *= _64e16;  exp -= 16; }
    while( r < 0.5/_64e4  && exp > -1021 ){ r *= _64e4;   exp -= 4; }
    while( r < 0.5/64.0   && exp > -1024 ){ r *= 64.0;    exp -= 1; }
  }else if( r>=0.5 ){
    while( r >= 0.5*_64e63 && exp < 960  ){ r *= 1.0/_64e64; exp += 64; }
    while( r >= 0.5*_64e15 && exp < 1008 ){ r *= 1.0/_64e16; exp += 16; }
    while( r >= 0.5*_64e3  && exp < 1020 ){ r *= 1.0/_64e4;  exp += 4; }
    while( r >= 0.5        && exp < 1023 ){ r *= 1.0/64.0;   exp += 1; }
  }
  if( neg ){
    exp = -exp;
    r = -r;
  }
  exp += 1024;
  r += 0.5;
  if( exp<0 ) return;
  if( exp>=2048 || r>=1.0 ){
    strcpy(z, "~~~~~~~~~~~~");
    return;
  }
  *z++ = zDigit[(exp>>6)&0x3f];
  *z++ = zDigit[exp & 0x3f];
  while( r>0.0 && cnt<10 ){
    int digit;
    r *= 64.0;
    digit = (int)r;
    assert( digit>=0 && digit<64 );
    *z++ = zDigit[digit & 0x3f];
    r -= digit;
    cnt++;
  }
  *z = 0;
}

#ifdef SQLITE_UTF8
/*
** X is a pointer to the first byte of a UTF-8 character.  Increment
** X so that it points to the next character.  This only works right
** if X points to a well-formed UTF-8 string.
*/
#define sqliteNextChar(X)  while( (0xc0&*++(X))==0x80 ){}