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small speedup for reduceh

This commit is contained in:
John Cupitt 2016-08-01 12:04:15 +01:00
parent 039997780b
commit ff819bfe63
2 changed files with 17 additions and 2 deletions
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2
libvips/iofuncs/region.c
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@ -890,7 +890,7 @@ vips_region_fill( VipsRegion *reg, VipsRect *r, VipsRegionFillFn fn, void *a )
* the pixels we need. If it does, we could copy them and only
* generate the new ones.
*
* However, we usually have neighboring regions on different threads,
* However, we usually have neighbouring regions on different threads,
* so from the point of view of this thread, we will get no overlaps
* on successive prepare requests.
*/

17
libvips/resample/reduceh.cpp
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@ -321,15 +321,30 @@ vips_reduceh_gen( VipsRegion *out_region, void *seq,
VIPS_GATE_START( "vips_reduceh_gen: work" );
for( int y = 0; y < r->height; y ++ ) {
VipsPel *p0;
VipsPel *q;
double X;
q = VIPS_REGION_ADDR( out_region, r->left, r->top + y );
X = r->left * reduceh->xshrink;
/* We want p0 to be the start (ie. x == 0) of the input
* scanline we are reading from. We can then calculate the p we
* need for each pixel with a single mul and avoid calling ADDR
* for each pixel.
*
* We can't get p0 directly with ADDR since it could be outside
* valid, so get the leftmost pixel in valid and subtract a
* bit.
*/
p0 = VIPS_REGION_ADDR( ir, ir->valid.left, r->top + y ) -
ir->valid.left * ps;
for( int x = 0; x < r->width; x++ ) {
int ix = (int) X;
VipsPel *p = VIPS_REGION_ADDR( ir, ix, r->top + y );
VipsPel *p = p0 + ix * ps;
const int sx = X * VIPS_TRANSFORM_SCALE * 2;
const int six = sx & (VIPS_TRANSFORM_SCALE * 2 - 1);
const int tx = (six + 1) >> 1;