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speedup rational_FromDouble

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multiplying/dividing by a power of 2 is much cheaper than
the equivalent operation on a factor of 10.

Change-Id: I31a7196a07649336378be867c67eb8a89fe6765f
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/108019
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>
This commit is contained in:
Noel Grandin
2020-12-19 16:05:20 +01:00
committed by Noel Grandin
parent 71a0bd756d
commit 67d83e40e2
1 changed files with 5 additions and 5 deletions
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tools/source/generic/fract.cxx
+5 -5
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@@ -400,8 +400,8 @@ SvStream& WriteFraction( SvStream& rOStream, const Fraction& rFract )
}
// If dVal > LONG_MAX or dVal < LONG_MIN, the rational throws a boost::bad_rational.
// Otherwise, dVal and denominator are multiplied by 10, until one of them
// is larger than (LONG_MAX / 10).
// Otherwise, dVal and denominator are multiplied by 8, until one of them
// is larger than (LONG_MAX / 8).
//
// NOTE: here we use 'sal_Int32' due that only values in sal_Int32 range are valid.
static boost::rational<sal_Int32> rational_FromDouble(double dVal)
@@ -411,11 +411,11 @@ static boost::rational<sal_Int32> rational_FromDouble(double dVal)
std::isnan(dVal) )
throw boost::bad_rational();
const sal_Int32 nMAX = std::numeric_limits<sal_Int32>::max() / 10;
const sal_Int32 nMAX = std::numeric_limits<sal_Int32>::max() / 8;
sal_Int32 nDen = 1;
while ( std::abs( dVal ) < nMAX && nDen < nMAX ) {
dVal *= 10;
nDen *= 10;
dVal *= 8;
nDen *= 8;
}
return boost::rational<sal_Int32>( sal_Int32(dVal), nDen );
}