im_conv() bug fixed

there was a typo in overflow estimation which could cause vips to use
the vector path when it should not, resulting in errors

ChangeLog

@@ -55,6 +55,7 @@
 - im_bufjpeg2vips() has a "header_only" parameter
 - added vips_image_get_data()
 - updated German translation (thanks Chris)
+- fixed typo in im_conv() overflow estimation which could cause errors
 
 30/11/10 started 7.24.0
 - bump for new stable

libvips/convolution/im_conv.c

@@ -63,6 +63,8 @@
  * 	  keeping two versions
  * 8/11/10
  * 	- add array tiling
+ * 9/5/11
+ * 	- argh typo in overflow estimation could cause errors
  */
 
 /*
@@ -110,6 +112,9 @@
 
 	- make up a signed 8-bit code path?
 
+	- don't use divluw, it's insanely slow, instead scale coefficients so 
+	  that we can just do >>8 at the end
+
  */
 
 #ifdef HAVE_CONFIG_H
@@ -355,10 +360,8 @@ conv_compile_convolution_u8s16( Conv *conv )
 	for( i = 0; i < n_mask; i++ ) {
 		int v = 255 * mask->coeff[i];
 
-		if( min + v < min )
-			min += v;
-		else if( min + v > max )
-			max += v;
+		min = IM_MIN( min, min + v );
+		max = IM_MAX( max, max + v );
 
 		if( max > SHRT_MAX )
 			return( -1 );
@@ -1008,6 +1011,11 @@ im_conv_raw( IMAGE *in, IMAGE *out, INTMASK *mask )
 	Conv *conv;
 	im_generate_fn generate;
 
+#ifdef DEBUG
+	printf( "im_conv_raw: starting with matrix:\n" );
+	im_print_imask( mask );
+#endif /*DEBUG*/
+
 	/* Check parameters.
 	 */
 	if( im_piocheck( in, out ) ||

libvips/iofuncs/vector.c

@@ -43,8 +43,8 @@
  */
 
 /*
-#define DEBUG
  */
+#define DEBUG
 
 #ifdef HAVE_CONFIG_H
 #include <config.h>
@@ -312,7 +312,7 @@ vips_vector_print( VipsVector *vector )
 	if( vector->compiled )
 		printf( "successfully compiled\n" );
 	else
-		printf( "not compiled successfully\n" );
+		printf( "not compiled\n" );
 	printf( "  n_scanline = %d\n", vector->n_scanline );
 	for( i = 0; i < vector->n_scanline; i++ )
 		printf( "        var %d = line %d\n",