better gauss mat generation

TODO

@@ -1,3 +1,5 @@
+- rename l3 on top of reduce
+
 - need tests for reducel3, test every kernel plues every numeric type
 
 - removed the cache from resize since we no longer sharpen, can we get
@@ -5,9 +7,6 @@
 
   seeeeeeems ok?
 
-- what demand hint are we setting for the reduce / shrink funcs?
-
-
 
 
 - try SEQ_UNBUFFERED on jpg source, get out of order error?

libvips/create/gaussmat.c

@@ -20,6 +20,7 @@
  * 	- use @precision, not @integer
  * 10/3/16
  * 	- allow 1x1 masks
+ * 	- better size calc
  */
 
 /*
@@ -132,7 +133,7 @@ vips_gaussmat_build( VipsObject *object )
 		vips_error( class->nickname, "%s", _( "mask too large" ) );
 		return( -1 );
 	}
-	width = x * 2 + 1;
+	width = 2 * x - 1;
 	height = gaussmat->separable ? 1 : width; 
 
 	vips_image_init_fields( create->out,

libvips/resample/resize.c

@@ -146,14 +146,13 @@ vips_resize_build( VipsObject *object )
 	/* If the final affine will be doing a large downsample, we can get 
 	 * nasty aliasing on hard edges. Blur before affine to smooth this out.
 	 *
-	 * Don't blur for very small shrinks, blur with radius 1 for x1.5
-	 * shrinks, blur radius 2 for x2.5 shrinks and above, etc.
+	 * Don't blur for very small shrinks, start to blur above about .5.
 	 *
 	 * Don't try to be clever for non-rectangular shrinks. We just
 	 * consider the horizontal factor.
 	 */
 	sigma = ((1.0 / hresidual) - 0.5) / 2.5;
-	anti_alias = hresidual < 0.9 && sigma > 0.1;
+	anti_alias = hresidual < 0.9 && sigma > 0.5;
 	if( anti_alias ) { 
 		vips_info( class->nickname, "anti-alias sigma %g", sigma );
 		if( vips_gaussblur( in, &t[1], sigma, NULL ) )