Path: utzoo!utgpu!water!watmath!clyde!rutgers!mit-eddie!bloom-beacon!oberon!cit-vax!tim
From: tim@cit-vax.Caltech.Edu (Timothy L. Kay)
Newsgroups: comp.sys.ibm.pc
Subject: bug in Turbo C 1.5
Message-ID: <5298@cit-vax.Caltech.Edu>
Date: 23 Jan 88 23:10:36 GMT
Reply-To: tim@cit-vax.UUCP (Timothy L. Kay)
Organization: California Institute of Technology
Lines: 69

To the best of my recollection, I don't recall having seen any bug
reports so far for Turbo C 1.5.  Am I the first person to report a
bug in Turbo C 1.5?

This program

	----------------------------------
	#include <string.h>

	void main() {
	  char *s = "this is a test";
	  printf("%s\n", s);
	  memcpy(s + 1, s, strlen(s) - 1);
	  printf("%s\n", s);
	}
	----------------------------------

displays

	--------------
	this is a test
	tthis is a tes
	--------------

under Turbo C 1.0, and

	--------------
	this is a test
	tthhssii    ee
	--------------

under Turbo C 1.5.

The Turbo C 1.0 memcpy() detects if the source and destination
overlap and switches the direction of the copying.  Borland must have
decided that the memcpy() routine should not be so smart.  The Turbo
C 1.5 memcpy() generates the above (rather peculiar) pattern by doing
word-at-a-time copying, always in the positive direction.

To see how the pattern was generated, we should look at the copy one
word at a time.  The ^^ marks the word to be moved.  The destination
of the move is marked by the second ^.

	--------------
	this is a test
	^^
	tths is a test
	  ^^
	tthhsis a test
	    ^^
	tthhssi a test
	      ^^
	tthhssii  test
	        ^^
	tthhssii   est
	          ^^
	tthhssii    et
	            ^^
	tthhssii    ee
	--------------

I have worked around this bug by extracting the old version out of
the old library.

	tlib /C \tc10\lib\ch.lib *memcpy.obj

Then I added "memcpy.obj" to my project, and it works.

Tim