devtools/eigen
1
0
Fork 0
mirror of https://gitlab.com/libeigen/eigen.git synced 2026-04-10 11:34:33 +08:00
Code Issues Packages Projects Releases Wiki Activity

Add a portable log2 function for integers

Browse Source
This commit is contained in:
Gael Guennebaud
2014-09-17 09:56:07 +02:00
parent 0f0580b97c
commit fc23e93707
2 changed files with 16 additions and 1 deletions
Download Patch File Download Diff File Expand all files Collapse all files

15
Eigen/src/Core/MathFunctions.h
View File

@@ -694,6 +694,21 @@ bool (isfinite)(const std::complex<T>& x)
return isfinite(real(x)) && isfinite(imag(x));
}
// Log base 2 for 32 bits positive integers.
// Conveniently returns 0 for x==0.
int log2(int x)
{
eigen_assert(x>=0);
unsigned int v(x);
static const int table[32] = { 0, 9, 1, 10, 13, 21, 2, 29, 11, 14, 16, 18, 22, 25, 3, 30, 8, 12, 20, 28, 15, 17, 24, 7, 19, 27, 23, 6, 26, 5, 4, 31 };
v |= v >> 1;
v |= v >> 2;
v |= v >> 4;
v |= v >> 8;
v |= v >> 16;
return table[(v * 0x07C4ACDDU) >> 27];
}
} // end namespace numext
namespace internal {