From c96367854991dde1a0162349221a103d75853186 Mon Sep 17 00:00:00 2001
From: John Cupitt <jcupitt@gmail.com>
Date: Sun, 22 Jan 2017 10:36:07 +0000
Subject: [PATCH] more hist_local fixups

add tests, add restrict
---
 libvips/histogram/hist_local.c | 21 ++++++++++++---------
 test/test_histogram.py         |  7 +++++++
 2 files changed, 19 insertions(+), 9 deletions(-)

diff --git a/libvips/histogram/hist_local.c b/libvips/histogram/hist_local.c
index 950074bc..b1085053 100644
--- a/libvips/histogram/hist_local.c
+++ b/libvips/histogram/hist_local.c
@@ -172,10 +172,12 @@ vips_hist_local_generate( VipsRegion *or,
 	for( y = 0; y < r->height; y++ ) {
 		/* Get input and output pointers for this line.
 		 */
-		VipsPel *p = VIPS_REGION_ADDR( seq->ir, r->left, r->top + y );
-		VipsPel *q = VIPS_REGION_ADDR( or, r->left, r->top + y );
+		VipsPel * restrict p = 
+			VIPS_REGION_ADDR( seq->ir, r->left, r->top + y );
+		VipsPel * restrict q = 
+			VIPS_REGION_ADDR( or, r->left, r->top + y );
 
-		VipsPel *p1;
+		VipsPel * restrict p1;
 		int x, i, j, b;
 
 		/* Find histogram for start of this line.
@@ -197,8 +199,8 @@ vips_hist_local_generate( VipsRegion *or,
 			for( b = 0; b < bands; b++ ) {
 				/* Sum histogram up to current pel.
 				 */
-				unsigned int *hist = seq->hist[b]; 
-				const int target = p[centre];
+				unsigned int * restrict hist = seq->hist[b]; 
+				const int target = p[centre + b];
 				const int max_slope = local->max_slope;
 
 				int sum;
@@ -251,23 +253,24 @@ vips_hist_local_generate( VipsRegion *or,
 				 * Scale by 255, not 256, or we'll get
 				 * overflow.
 				 */
-				*q++ = 255 * sum / 
+				q[b] = 255 * sum / 
 					(local->width * local->height);
 
 				/* Adapt histogram --- remove the pels from 
 				 * the left hand column, add in pels for a 
 				 * new right-hand column.
 				 */
-				p1 = p;
+				p1 = p + b;
 				for( j = 0; j < local->height; j++ ) {
 					hist[p1[0]] -= 1;
 					hist[p1[bands * local->width]] += 1;
 
 					p1 += lsk;
 				}
-
-				p += 1;
 			}
+
+			p += bands;
+			q += bands;
 		}
 	}
 
diff --git a/test/test_histogram.py b/test/test_histogram.py
index dbacba5d..43a32cba 100755
--- a/test/test_histogram.py
+++ b/test/test_histogram.py
@@ -74,6 +74,13 @@ class TestHistogram(unittest.TestCase):
         self.assertTrue(im.avg() < im2.avg())
         self.assertTrue(im.deviate() < im2.deviate())
 
+        im3 = im.hist_local(10, 10, max_slope = 3)
+
+        self.assertEqual(im.width, im2.width)
+        self.assertEqual(im.height, im2.height)
+
+        self.assertTrue(im3.deviate() < im2.deviate())
+
     def test_hist_match(self):
         im = Vips.Image.identity()
         im2 = Vips.Image.identity()