[PATCH] Fix determination of lower precision in __mul

[Andreas Jaeger]

On 02/13/2013 04:05 PM, Siddhesh Poyarekar wrote:
> Hi,
>
> I introduced a dormant buglet when I committed the patch that skips
> multiplication of zeroes.  The loop to determine the lower precision
> of the two input numbers is buggy since it checks X[i] * Y[i] to be
> non-zero to ensure that both mantissa digits are non-zero.  This is a
> wrong check though since we could have numbers that have mantissa as
> such:
>
> X = {1, 0, 0, 1, 0, 0}
> Y = {1, 1, 1, 0, 0, 0}
>
> Here, the higher precision (ip2) ought to be 3 and the lower (ip)
> ought to be 2.  The product check however makes the lower one as 0.  I
> didn't find any input that actually triggered this bug, but here's a
> patch to fix it anyway.  I had written it some time back, but it was
> on another branch and had forgotten to update the submitted patch;
> sorry about that.
>
> Verified that it does not cause any regressions in the testsuite.  OK
> to commit?

yes, this is ok,

Andreas
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