Tweak image decode downscale factor internals.

When calculating the factor to use for image downscales, calculate it
as a shift rather than a divisor.

4 files changed, 35 insertions, 34 deletions

diff --git a/fitz/filt_dctd.c b/fitz/filt_dctd.c
index 76f82abe..3503370d 100644
--- a/fitz/filt_dctd.c
+++ b/fitz/filt_dctd.c
@@ -12,7 +12,7 @@ struct fz_dctd_s
 	int color_transform;
 	int init;
 	int stride;
-	int factor;
+	int l2factor;
 	unsigned char *scanline;
 	unsigned char *rp, *wp;
 	struct jpeg_decompress_struct cinfo;
@@ -157,7 +157,7 @@ read_dctd(fz_stream *stm, unsigned char *buf, int len)
 			break;
 		}
 
-		cinfo->scale_num = 8/state->factor;
+		cinfo->scale_num = 8/(1<<state->l2factor);
 		cinfo->scale_denom = 8;
 
 		jpeg_start_decompress(cinfo);
@@ -228,7 +228,7 @@ fz_open_dctd(fz_stream *chain, int color_transform)
 }
 
 fz_stream *
-fz_open_resized_dctd(fz_stream *chain, int color_transform, int factor)
+fz_open_resized_dctd(fz_stream *chain, int color_transform, int l2factor)
 {
 	fz_context *ctx = chain->ctx;
 	fz_dctd *state = NULL;
@@ -242,7 +242,7 @@ fz_open_resized_dctd(fz_stream *chain, int color_transform, int factor)
 		state->chain = chain;
 		state->color_transform = color_transform;
 		state->init = 0;
-		state->factor = factor;
+		state->l2factor = l2factor;
 	}
 	fz_catch(ctx)
 	{
diff --git a/fitz/fitz-internal.h b/fitz/fitz-internal.h
index 043449db..528fb50a 100644
--- a/fitz/fitz-internal.h
+++ b/fitz/fitz-internal.h
@@ -753,7 +753,7 @@ fz_stream *fz_open_a85d(fz_stream *chain);
 fz_stream *fz_open_ahxd(fz_stream *chain);
 fz_stream *fz_open_rld(fz_stream *chain);
 fz_stream *fz_open_dctd(fz_stream *chain, int color_transform);
-fz_stream *fz_open_resized_dctd(fz_stream *chain, int color_transform, int factor);
+fz_stream *fz_open_resized_dctd(fz_stream *chain, int color_transform, int l2factor);
 fz_stream *fz_open_faxd(fz_stream *chain,
 	int k, int end_of_line, int encoded_byte_align,
 	int columns, int rows, int end_of_block, int black_is_1);
@@ -845,7 +845,7 @@ typedef struct fz_compressed_buffer_s fz_compressed_buffer;
 unsigned int fz_compressed_buffer_size(fz_compressed_buffer *buffer);
 
 fz_stream *fz_open_compressed_buffer(fz_context *ctx, fz_compressed_buffer *);
-fz_stream *fz_open_image_decomp_stream(fz_context *ctx, fz_compressed_buffer *, int *factor);
+fz_stream *fz_open_image_decomp_stream(fz_context *ctx, fz_compressed_buffer *, int *l2factor);
 
 enum
 {
diff --git a/fitz/stm_comp_buf.c b/fitz/stm_comp_buf.c
index 54653536..7fa48cb0 100644
--- a/fitz/stm_comp_buf.c
+++ b/fitz/stm_comp_buf.c
@@ -15,7 +15,7 @@ fz_free_compressed_buffer(fz_context *ctx, fz_compressed_buffer *buf)
 
 
 fz_stream *
-fz_open_image_decomp_stream(fz_context *ctx, fz_compressed_buffer *buffer, int *factor)
+fz_open_image_decomp_stream(fz_context *ctx, fz_compressed_buffer *buffer, int *l2factor)
 {
 	fz_stream *chain = fz_open_buffer(ctx, buffer->buffer);
 	fz_compression_params *params = &buffer->params;
@@ -23,7 +23,7 @@ fz_open_image_decomp_stream(fz_context *ctx, fz_compressed_buffer *buffer, int *
 	switch (params->type)
 	{
 	case FZ_IMAGE_FAX:
-		*factor = 1;
+		*l2factor = 0;
 		return fz_open_faxd(chain,
 				params->u.fax.k,
 				params->u.fax.end_of_line,
@@ -33,26 +33,26 @@ fz_open_image_decomp_stream(fz_context *ctx, fz_compressed_buffer *buffer, int *
 				params->u.fax.end_of_block,
 				params->u.fax.black_is_1);
 	case FZ_IMAGE_JPEG:
-		if (*factor > 8)
-			*factor = 8;
-		return fz_open_resized_dctd(chain, params->u.jpeg.color_transform, *factor);
+		if (*l2factor > 8)
+			*l2factor = 8;
+		return fz_open_resized_dctd(chain, params->u.jpeg.color_transform, *l2factor);
 	case FZ_IMAGE_RLD:
-		*factor = 1;
+		*l2factor = 0;
 		return fz_open_rld(chain);
 	case FZ_IMAGE_FLATE:
-		*factor = 1;
+		*l2factor = 0;
 		chain = fz_open_flated(chain);
 		if (params->u.flate.predictor > 1)
 			chain = fz_open_predict(chain, params->u.flate.predictor, params->u.flate.columns, params->u.flate.colors, params->u.flate.bpc);
 		return chain;
 	case FZ_IMAGE_LZW:
-		*factor = 1;
+		*l2factor = 0;
 		chain = fz_open_lzwd(chain, params->u.lzw.early_change);
 		if (params->u.lzw.predictor > 1)
 			chain = fz_open_predict(chain, params->u.lzw.predictor, params->u.lzw.columns, params->u.lzw.colors, params->u.lzw.bpc);
 		return chain;
 	default:
-		*factor = 1;
+		*l2factor = 0;
 		break;
 	}
 
@@ -62,9 +62,9 @@ fz_open_image_decomp_stream(fz_context *ctx, fz_compressed_buffer *buffer, int *
 fz_stream *
 fz_open_compressed_buffer(fz_context *ctx, fz_compressed_buffer *buffer)
 {
-	int factor = 1;
+	int l2factor = 0;
 
-	return fz_open_image_decomp_stream(ctx, buffer, &factor);
+	return fz_open_image_decomp_stream(ctx, buffer, &l2factor);
 }
 
 unsigned int
diff --git a/pdf/pdf_image.c b/pdf/pdf_image.c
index 262be821..27a13100 100644
--- a/pdf/pdf_image.c
+++ b/pdf/pdf_image.c
@@ -6,7 +6,7 @@ typedef struct pdf_image_key_s pdf_image_key;
 struct pdf_image_key_s {
 	int refs;
 	fz_image *image;
-	int factor;
+	int l2factor;
 };
 
 static void pdf_load_jpx(pdf_document *xref, pdf_obj *dict, pdf_image *image);
@@ -36,7 +36,7 @@ pdf_make_hash_image_key(fz_store_hash *hash, void *key_)
 	pdf_image_key *key = (pdf_image_key *)key_;
 
 	hash->u.pi.ptr = key->image;
-	hash->u.pi.i = key->factor;
+	hash->u.pi.i = key->l2factor;
 	return 1;
 }
 
@@ -74,7 +74,7 @@ pdf_cmp_image_key(void *k0_, void *k1_)
 	pdf_image_key *k0 = (pdf_image_key *)k0_;
 	pdf_image_key *k1 = (pdf_image_key *)k1_;
 
-	return k0->image == k1->image && k0->factor == k1->factor;
+	return k0->image == k1->image && k0->l2factor == k1->l2factor;
 }
 
 #ifndef NDEBUG
@@ -83,7 +83,7 @@ pdf_debug_image(void *key_)
 {
 	pdf_image_key *key = (pdf_image_key *)key_;
 
-	printf("(image %d x %d sf=%d) ", key->image->w, key->image->h, key->factor);
+	printf("(image %d x %d sf=%d) ", key->image->w, key->image->h, key->l2factor);
 }
 #endif
 
@@ -99,14 +99,15 @@ static fz_store_type pdf_image_store_type =
 };
 
 static fz_pixmap *
-decomp_image_from_stream(fz_context *ctx, fz_stream *stm, pdf_image *image, int in_line, int indexed, int factor, int cache)
+decomp_image_from_stream(fz_context *ctx, fz_stream *stm, pdf_image *image, int in_line, int indexed, int l2factor, int cache)
 {
 	fz_pixmap *tile = NULL;
 	fz_pixmap *existing_tile;
 	int stride, len, i;
 	unsigned char *samples = NULL;
-	int w = (image->base.w + (factor-1)) / factor;
-	int h = (image->base.h + (factor-1)) / factor;
+	int f = 1<<l2factor;
+	int w = (image->base.w + f-1) >> l2factor;
+	int h = (image->base.h + f-1) >> l2factor;
 	pdf_image_key *key;
 
 	fz_var(tile);
@@ -204,7 +205,7 @@ decomp_image_from_stream(fz_context *ctx, fz_stream *stm, pdf_image *image, int
 		key = fz_malloc_struct(ctx, pdf_image_key);
 		key->refs = 1;
 		key->image = fz_keep_image(ctx, &image->base);
-		key->factor = factor;
+		key->l2factor = l2factor;
 		existing_tile = fz_store_item(ctx, key, tile, fz_pixmap_size(ctx, tile), &pdf_image_store_type);
 		if (existing_tile)
 		{
@@ -246,7 +247,7 @@ pdf_image_get_pixmap(fz_context *ctx, fz_image *image_, int w, int h)
 	pdf_image *image = (pdf_image *)image_;
 	fz_pixmap *tile;
 	fz_stream *stm;
-	int factor;
+	int l2factor;
 	pdf_image_key key;
 
 	/* Check for 'simple' images which are just pixmaps */
@@ -266,27 +267,27 @@ pdf_image_get_pixmap(fz_context *ctx, fz_image *image_, int w, int h)
 
 	/* What is our ideal factor? */
 	if (w == 0 || h == 0)
-		factor = 1;
+		l2factor = 0;
 	else
-		for (factor=1; image->base.w/(2*factor) >= w && image->base.h/(2*factor) >= h && factor < 8; factor *= 2);
+		for (l2factor=0; image->base.w>>(l2factor+1) >= w && image->base.h>>(l2factor+1) >= h && l2factor < 8; l2factor++);
 
 	/* Can we find any suitable tiles in the cache? */
 	key.refs = 1;
 	key.image = &image->base;
-	key.factor = factor;
+	key.l2factor = l2factor;
 	do
 	{
 		tile = fz_find_item(ctx, fz_free_pixmap_imp, &key, &pdf_image_store_type);
 		if (tile)
 			return tile;
-		key.factor >>= 1;
+		key.l2factor--;
 	}
-	while (key.factor > 0);
+	while (key.l2factor >= 0);
 
 	/* We need to make a new one. */
-	stm = fz_open_image_decomp_stream(ctx, image->buffer, &factor);
+	stm = fz_open_image_decomp_stream(ctx, image->buffer, &l2factor);
 
-	return decomp_image_from_stream(ctx, stm, image, 0, 0, factor, 1);
+	return decomp_image_from_stream(ctx, stm, image, 0, 0, l2factor, 1);
 }
 
 static pdf_image *
@@ -449,7 +450,7 @@ pdf_load_image_imp(pdf_document *xref, pdf_obj *rdb, pdf_obj *dict, fz_stream *c
 			stm = pdf_open_stream(xref, pdf_to_num(dict), pdf_to_gen(dict));
 		}
 
-		image->tile = decomp_image_from_stream(ctx, stm, image, cstm != NULL, indexed, 1, 0);
+		image->tile = decomp_image_from_stream(ctx, stm, image, cstm != NULL, indexed, 0, 0);
 	}
 	fz_catch(ctx)
 	{