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one less comparison per channel in the nohalo.cpp code

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This commit is contained in:
Nicolas Robidoux 2010-05-19 20:32:08 +00:00
parent c7cac74765
commit 94c0e0bbd8
1 changed files with 42 additions and 23 deletions
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65
libvips/resample/nohalo.cpp
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@ -763,9 +763,10 @@ lbbicubic( const double c00,
* Computation of the four min and four max over 3x3 input data
* sub-blocks of the 4x4 input stencil.
*
* Surprisingly, we have not succeeded in using the fact that the
* data comes from the (co-monotone) method Nohalo so that it is
* known ahead of time that
* Surprisingly, we have not succeeded in reducing the number of
* comparisons needed by using the fact that the data comes from the
* (co-monotone) method Nohalo so that it is known ahead of time
* that
*
* dos_thr is between dos_two and dos_fou
*
@ -783,42 +784,60 @@ lbbicubic( const double c00,
*
* "min(b,c) <= a <= max(b,c)".)
*
* We have, however, succeeded in eliminating one flag
* computation/the use of one intermediate result. See the two
* commented out lines below.
*
* Overall, only 27 comparisons are needed (to compute 4 mins and 4
* maxes!). Without the simplication, 28 comparisoins would be used.
*
* Suggestions welcome!
*/
const double m1 = (dos_two <= dos_thr) ? dos_two : dos_thr ;
const double M1 = (dos_two <= dos_thr) ? dos_thr : dos_two ;
const double m2 = (tre_two <= tre_thr) ? tre_two : tre_thr ;
const double M2 = (tre_two <= tre_thr) ? tre_thr : tre_two ;
const double m3 = (uno_two <= uno_thr) ? uno_two : uno_thr ;
const double M3 = (uno_two <= uno_thr) ? uno_thr : uno_two ;
const double m4 = (qua_two <= qua_thr) ? qua_two : qua_thr ;
const double M4 = (qua_two <= qua_thr) ? qua_thr : qua_two ;
const double m3 = (uno_two <= uno_thr) ? uno_two : uno_thr ;
const double M3 = (uno_two <= uno_thr) ? uno_thr : uno_two ;
const double m5 = LBB_MIN( m1, m2 );
const double M5 = LBB_MAX( M1, M2 );
const double m6 = (dos_one <= tre_one) ? dos_one : tre_one ;
const double M6 = (dos_one <= tre_one) ? tre_one : dos_one ;
const double m7 = (dos_fou <= tre_fou) ? dos_fou : tre_fou ;
const double M7 = (dos_fou <= tre_fou) ? tre_fou : dos_fou ;
const double m8 = LBB_MIN( m5, m3 );
const double M8 = LBB_MAX( M5, M3 );
const double m13 = (dos_fou <= qua_fou) ? dos_fou : qua_fou ;
const double M13 = (dos_fou <= qua_fou) ? qua_fou : dos_fou ;
/*
* Because the data comes from Nohalo subdivision, the following two
* lines can be replaced by the above, simpler, two lines without
* changing the results.
*
* const double m13 = LBB_MIN( m7, qua_fou );
* const double M13 = LBB_MAX( M7, qua_fou );
*
* This also allows reodering the comparisons to put space between
* the computation of a result and its use.
*/
const double m9 = LBB_MIN( m5, m4 );
const double M9 = LBB_MAX( M5, M4 );
const double m10 = LBB_MIN( m6, uno_one );
const double M10 = LBB_MAX( M6, uno_one );
const double m8 = LBB_MIN( m5, m3 );
const double M8 = LBB_MAX( M5, M3 );
const double m11 = LBB_MIN( m6, qua_one );
const double M11 = LBB_MAX( M6, qua_one );
const double m10 = LBB_MIN( m6, uno_one );
const double M10 = LBB_MAX( M6, uno_one );
const double m12 = LBB_MIN( m7, uno_fou );
const double M12 = LBB_MAX( M7, uno_fou );
const double m13 = LBB_MIN( m7, qua_fou );
const double M13 = LBB_MAX( M7, qua_fou );
const double min00 = LBB_MIN( m8, m10 );
const double max00 = LBB_MAX( M8, M10 );
const double min01 = LBB_MIN( m9, m11 );
const double max01 = LBB_MAX( M9, M11 );
const double min10 = LBB_MIN( m8, m12 );
const double max10 = LBB_MAX( M8, M12 );
const double min11 = LBB_MIN( m9, m13 );
const double max11 = LBB_MAX( M9, M13 );
const double min01 = LBB_MIN( m9, m11 );
const double max01 = LBB_MAX( M9, M11 );
const double min00 = LBB_MIN( m8, m10 );
const double max00 = LBB_MAX( M8, M10 );
const double min10 = LBB_MIN( m8, m12 );
const double max10 = LBB_MAX( M8, M12 );
/*
* The remainder of the "per channel" computation involves the
* computation of:
@ -845,14 +864,14 @@ lbbicubic( const double c00,
/*
* Distances to the local min and max:
*/
const double u00 = dos_two - min00;
const double v00 = max00 - dos_two;
const double u01 = tre_two - min01;
const double v01 = max01 - tre_two;
const double u10 = dos_thr - min10;
const double v10 = max10 - dos_thr;
const double u11 = tre_thr - min11;
const double v11 = max11 - tre_thr;
const double u01 = tre_two - min01;
const double v01 = max01 - tre_two;
const double u00 = dos_two - min00;
const double v00 = max00 - dos_two;
const double u10 = dos_thr - min10;
const double v10 = max10 - dos_thr;
/*
* Initial values of the derivatives computed with centered