hoover@cs.UAlberta.CA (Jim Hoover) (12/11/90)
Larry: On my SCO box, perl failed the lib.big test for big integers. In tracking down the failure I discovered a bug in the implementation of cmp or of str_cmp (take your pick). The cmp operator implementation assumes that str_cmp (in str.c) returns one of -1 0 +1. str_cmp is implemented with memcmp, which is specified (on my SCO box) only to return a negative, zero, or positive value. It says nothing about the range of values. SCO's version returns various postive and negative values. Jim Hoover Here is my fix to str_cmp: 741c741,742 < return retval; --- > /* FIX - memcmp is not guaranteed to return -1 0 +1, just sign */ > return (retval > 0) ? +1 : -1; 746c747,748 < return retval; --- > /* FIX - memcmp is not guaranteed to return -1 0 +1, just sign */ > return (retval > 0) ? +1 : -1; -- Prof. Jim Hoover | Office +1 403 492 5401 or 5290 Dept. of Computing Science | FAX +1 403 492 1071 University of Alberta | hoover@cs.ualberta.ca Edmonton, Alberta, Canada T6G 2H1 |
gnb@bby.oz.au (Gregory N. Bond) (12/12/90)
>>>>> On 11 Dec 90 05:26:04 GMT, hoover@cs.UAlberta.CA (Jim Hoover) said:
Jim> 746c747,748
Jim> < return retval;
Jim> ---
Jim> /* FIX - memcmp is not guaranteed to return -1 0 +1, just sign */
Jim> return (retval > 0) ? +1 : -1;
Bzzt. What it retval == 0? You mean
return (retval > 0) ? 1 : (retval < 0) ? -1 : 0;
or perhaps
return (retval < 0) ? -1 : (retval > 0);
But you knew that...
--
Gregory Bond, Burdett Buckeridge & Young Ltd, Melbourne, Australia
Internet: gnb@melba.bby.oz.au non-MX: gnb%melba.bby.oz@uunet.uu.net
Uucp: {uunet,pyramid,ubc-cs,ukc,mcvax,prlb2,nttlab...}!munnari!melba.bby.oz!gnbhoover@cs.UAlberta.CA (Jim Hoover) (12/12/90)
In article <1990Dec11.220809.20201@melba.bby.oz.au> gnb@bby.oz.au (Gregory N. Bond) writes: >>>>>> On 11 Dec 90 05:26:04 GMT, hoover@cs.UAlberta.CA (Jim Hoover) said: > >Jim> 746c747,748 >Jim> < return retval; >Jim> --- >Jim> /* FIX - memcmp is not guaranteed to return -1 0 +1, just sign */ >Jim> return (retval > 0) ? +1 : -1; > >Bzzt. What it retval == 0? You mean > return (retval > 0) ? 1 : (retval < 0) ? -1 : 0; > ... Sorry, I seem to have become affected by the current trend toward obscurity disguised as cleverness. I could have at least practiced what I preach and given more context :) Within the context of the fix, retval cannot be 0, so the single test suffices. Here is the full context: if (str1->str_cur < str2->str_cur) { if (retval = memcmp(str1->str_ptr, str2->str_ptr, str1->str_cur)) /* HJH - memcmp is not guaranteed to return -1 0 +1, just sign */ return (retval > 0) ? +1 : -1; else return -1; } else if (retval = memcmp(str1->str_ptr, str2->str_ptr, str2->str_cur)) /* HJH - memcmp is not guaranteed to return -1 0 +1, just sign */ return (retval > 0) ? +1 : -1; else if (str1->str_cur == str2->str_cur) return 0; else return 1; (The context, by the way, reflects a two's complement bias that is ubiquitous in C code. How much stuff breaks if you switch to a signed-magnitude machine with +- 0?) >-- >Gregory Bond, Burdett Buckeridge & Young Ltd, Melbourne, Australia >Internet: gnb@melba.bby.oz.au non-MX: gnb%melba.bby.oz@uunet.uu.net >Uucp: {uunet,pyramid,ubc-cs,ukc,mcvax,prlb2,nttlab...}!munnari!melba.bby.oz!gnb -- Prof. Jim Hoover | Office +1 403 492 5401 or 5290 Dept. of Computing Science | FAX +1 403 492 1071 University of Alberta | hoover@cs.ualberta.ca Edmonton, Alberta, Canada T6G 2H1 |