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Re: PATCH: PR target/42542: Vectorizer produces incorrect results on max of signed intergers

On 01/05/2010 05:00 PM, H.J. Lu wrote:
On Tue, Jan 5, 2010 at 7:55 AM, Paolo Bonzini<bonzini@gnu.org> wrote:
I see no other way to fixup the underflow. Some comments below: 

You can always subtract (or XOR) the sign bit to turn an unsigned value to
the corresponding signed value.  The attached patch (on top of the code
before H.J.'s patch) fixes the C testcase in the PR, but I didn't test it
further and I don't have time unfortunately.

What is the the corresponding signed value of unsigned 0x8000000?

0 of course. For example

0x7FFFFFFF ltu 0x80000000 ltu 0x80000001

becomes after flipping the sign bit

0xFFFFFFFF < 0x00000000 < 0x00000001

which is just -1 < 0 < 1.

Paolo

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