Path: utzoo!utgpu!jarvis.csri.toronto.edu!clyde.concordia.ca!uunet!snorkelwacker!usc!randvax!salzman
From: salzman@randvax.UUCP (Isaac Salzman)
Newsgroups: gnu.g++.lib.bug
Subject: libg++-1.36.3: bug in Itolong (class Integer)
Message-ID: <2396@randvax.UUCP>
Date: 12 Feb 90 03:26:51 GMT
Reply-To: salzman@rand.org (Isaac Salzman)
Distribution: gnu
Organization: RAND Corp., Santa Monica, Ca.
Lines: 94

[built with g++ 1.36.4 on a Sparcstation-1] 

Itolong in Integer.cc is broken. For small Integers (those that take up only
1 short), there's a chance you'll get back garbage when you assign it to
a long. Here are the offending lines of code:

    /* what if rep->s[1] isn't defined??!! */

    unsigned long a = rep->s[SHORT_PER_LONG - 1]; 
    if (a >= I_MINNUM)
      return (rep->sgn == I_POSITIVE) ? MAXLONG : MINLONG;
    else
    {
	.
	.
	.

SHORT_PER_LONG ends up as 2, so if you're converting something that takes
only 1 short, there's a good chance that you'll get back MAXLONG or MINLONG,
depending on what happens to be in rep->s[1]. There are several ways to fix
this. However, Lou Moore (mooooore@rand.org) suggested a nice general
replacement for Itolong, so here are the context diff's:


*** Orig/Integer.cc	Mon Feb  5 15:31:29 1990
--- Integer.cc	Sun Feb 11 11:15:12 1990
***************
*** 343,374 ****
    return rep;
  }
  
- 
  // convert to a legal two's complement long if possible
  // if too big, return most negative/positive value
  
  long Itolong(const IntRep* rep)
  { 
!   if (rep->len > SHORT_PER_LONG)
      return (rep->sgn == I_POSITIVE) ? MAXLONG : MINLONG;
    else
    {
!     unsigned long a = rep->s[SHORT_PER_LONG - 1];
!     if (a >= I_MINNUM)
!       return (rep->sgn == I_POSITIVE) ? MAXLONG : MINLONG;
!     else
!     {
!       a = up(a) | rep->s[SHORT_PER_LONG - 2];
!       if (SHORT_PER_LONG - 3 >= 0)
        {
!         for (int i = SHORT_PER_LONG - 3; i >= 0; --i)
!           a = up(a) | rep->s[i];
        }
!       return (rep->sgn == I_POSITIVE)? a : -((long)a);
!     }
    }
  }
- 
  
  // test whether op long() will work.
  // careful about asymmetry between MINLONG & MAXLONG
--- 343,367 ----
    return rep;
  }
  
  // convert to a legal two's complement long if possible
  // if too big, return most negative/positive value
  
  long Itolong(const IntRep* rep)
  { 
!   int i = rep->len-1;
!   if (i >= SHORT_PER_LONG)
      return (rep->sgn == I_POSITIVE) ? MAXLONG : MINLONG;
    else
    {
!     unsigned long a = rep->s[i];
!     while (i > 0)
        {
! 	if ( (a = up(a) | rep->s[--i]) >= I_MINNUM)
! 	  return (rep->sgn == I_POSITIVE) ? MAXLONG : MINLONG;
        }
!     return (rep->sgn == I_POSITIVE)? a : -((long)a);
    }
  }
  
  // test whether op long() will work.
  // careful about asymmetry between MINLONG & MAXLONG

--
* Isaac J. Salzman                                            ----     
* The RAND Corporation - Information Sciences Dept.          /o o/  /  
* 1700 Main St., PO Box 2138, Santa Monica, CA 90406-2138    | v |  |  
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