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Simplify expresion

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Reduce operation count by space / speed tradeoff.
This expression is widely used in LO.
Then needs to be fast.

Change-Id: Ic88cf15d451ec95a8ad6da88cd9f601cf2876871
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/117954
Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>
Tested-by: Jenkins
This commit is contained in:
BaiXiaochun 2021-06-27 18:38:10 +02:00 committed by Mike Kaganski
parent a40334ef4d
commit 9c15dea0b2
1 changed files with 8 additions and 21 deletions
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29
sal/rtl/math.cxx
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@ -44,33 +44,20 @@
#include <dtoa.h>
int const n10Count = 16;
double const n10s[2][n10Count] = {
{ 1e1, 1e2, 1e3, 1e4, 1e5, 1e6, 1e7, 1e8,
1e9, 1e10, 1e11, 1e12, 1e13, 1e14, 1e15, 1e16 },
{ 1e-1, 1e-2, 1e-3, 1e-4, 1e-5, 1e-6, 1e-7, 1e-8,
1e-9, 1e-10, 1e-11, 1e-12, 1e-13, 1e-14, 1e-15, 1e-16 }
constexpr int n10Count = 16;
constexpr double n10s[n10Count*2+1] = {
1e-16, 1e-15, 1e-14, 1e-13, 1e-12, 1e-11, 1e-10, 1e-9,
1e-8, 1e-7, 1e-6, 1e-5, 1e-4, 1e-3, 1e-2, 1e-1, 1e0,
1e1, 1e2, 1e3, 1e4, 1e5, 1e6, 1e7, 1e8,
1e9, 1e10, 1e11, 1e12, 1e13, 1e14, 1e15, 1e16 ,
};
// return pow(10.0,nExp) optimized for exponents in the interval [-16,16]
static double getN10Exp(int nExp)
{
if (nExp < 0)
{
// && -nExp > 0 necessary for std::numeric_limits<int>::min()
// because -nExp = nExp
if (-nExp <= n10Count && -nExp > 0)
return n10s[1][-nExp-1];
if (nExp < -n10Count || nExp > n10Count)
return pow(10.0, static_cast<double>(nExp));
}
if (nExp > 0)
{
if (nExp <= n10Count)
return n10s[0][nExp-1];
return pow(10.0, static_cast<double>(nExp));
}
return 1.0;
return n10s[nExp + n10Count];
}
namespace {