Re: Integer overflow in operator new. Solved? Experimental i686 code.

Re: Integer overflow in operator new. Solved? Experimental i686 code.

[J.C. Pizarro]

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#include <stddef.h> // by J.C. Pîzarro

...

// This function doesn't touch the ECX register that is touched by OptionC.

__volatile__ static const int minus_one = -1;

void *__allocate_array_OptionD(size_t num, size_t size) {
   register unsigned int result;
   __asm__ __volatile__
   (
           "imull   %2" // See the flags OF, SF, CF, .. are affected or not.
    "\n\t" "cmovol %3,%%eax" // i dude if it works or not. Not tested ...
//    "\n\t" "cmovcl %3,%%eax"
    :"=a"(result)
    :"a"(num),"m"(size),"m"(minus_one)
    :"%edx"/*???*/); // There are 0 conditional jumps!!! hehehehe!
   return operator new[](result);
}

-----------------------------------------------------------------------------

* gcc version 4.1.3 20070326 (prerelease)
* 6 instructions of i686 !!! (cmovo came from i686)
* no conditional jump !!!

_Z24__allocate_array_OptionDjj:
	subl	$12, %esp            # <- unneeded
	movl	16(%esp), %eax
#APP
	imull   20(%esp)
	cmovol minus_one,%eax
#NO_APP
	movl	%eax, (%esp)         # <- better movl %eax, 4(%esp)
	call	_Znaj                # <- better jmp _Znaj
	addl	$12, %esp            # <- unneeded
	ret                          # <- unneeded

minus_one:
	.long	-1

-----------------------------------------------------------------------------

* hand-written
* 5 instructions of i686 !!! (cmovo came from i686)
* no conditional jump !!!

_Z24__allocate_array_OptionDjj:
	movl	4(%esp), %eax
#APP
	imull   8(%esp)
	cmovol minus_one,%eax
#NO_APP
	movl	%eax, 4(%esp)
	jmp	_Znaj

minus_one:
	.long	-1

-----------------------------------------------------------------------------

Here has reached 5 instructions.
Anyone with 4 instructions?

J.C. Pizarro

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Re: Integer overflow in operator new. Solved? Experimental i686 code.

[J.C. Pizarro]

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#include <stddef.h> // by J.C. Pîzarro

...

// See http://www.cs.sjsu.edu/~kirchher/CS047/multDiv.html
//     One-operand imul:   &   Unsigned mul:

// warning: 32 bit, i686, possible risk of -x * -y = valid x * y, ...
// warning: it's made quick & dirty, possible to give clobbered situations.
// warning: it is not ready for x86-64, ppc, ppc64, etc.
// NO WARRANTY!!! IT'S VERY EXPERIMENTAL!!! NOT TESTED YET!!!
void *__allocate_array_OptionC(size_t num, size_t size) {
   unsigned int result;
   __asm__ __volatile__
   (
           "orl $-1,%%ecx"
    "\n\t" "imull   %2" // See the flags OF, SF, CF, .. are affected or not.
    "\n\t" "cmovol %%ecx,%%eax" // i dude if it works or not. Not tested ...
//    "\n\t" "cmovcl %%ecx,%%eax"
    :"=a"(result)
    :"a"(num),"g"(size)
    :/*???*/); // There are 0 conditional jumps!!! hehehehe!
   return operator new[](result);
}

-----------------------------------------------------------------------------

* gcc version 4.1.3 20070326 (prerelease)
* 6 instructions of i686 !!! (cmovo came from i686)
* no conditional jump !!!

_Z24__allocate_array_OptionCjj:
	movl	4(%esp), %eax
#APP
	orl $-1,%ecx
	imull   8(%esp)
	cmovol %ecx,%eax
#NO_APP
	movl	%eax, 4(%esp)
	jmp	_Znaj

-----------------------------------------------------------------------------

J.C. Pizarro

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