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From: apm233m@vaxc.cc.monash.edu.au
Newsgroups: comp.lang.c++
Subject: Bug fix for Turbo C++ v1.0 ?
Message-ID: <1991Jun26.155459.86966@vaxc.cc.monash.edu.au>
Date: 26 Jun 91 05:54:59 GMT
Organization: Computer Centre, Monash University, Australia
Lines: 32

My question is: is there a patch for Turbo C++ v1.0 to fix the following
code generation bug?

The bug concerns the code generated for a right shift of longs.

The following short program demonstrates the bug.

   main()
   {
   long bad=-2, good=-4;
   printf("Is this true?: -1=%ld, -1=%ld\n", bad >> 1, good >> 2);
   }

My copy of TC++ generates an .exe which produces:
   Is this true?: -1=2147483647, -1=-1

This bug occurs only for shifts of longs, and only if the shift is
by the constant "1". It is a bug in the generated code; the preprocessor
does not have the bug and therefore cannot be used to detect the bug.
The actual generated code is:
	shr	ax,1
	rcr	dx,1
whereas the correct code would be:
	sar	ax,1
	rcr	dx,1

-- 
---------------
Bill Metzenthen
Mathematics Department
Monash University
Australia