pnmimagetypes: fix allocation efficiency in PNG reader

rdb · rdb · commit 42405dff2edd · 2018-12-30T20:13:12.000+01:00
Rather than making one allocation per row, it instead makes one allocation for all rows.
diff --git a/panda/src/pnmimagetypes/pnmFileTypePNG.cxx b/panda/src/pnmimagetypes/pnmFileTypePNG.cxx
@@ -338,11 +338,12 @@ read_data(xel *array, xelval *alpha_data) {
   // format, mainly because we keep array and alpha data separately, and there
   // doesn't appear to be good support to get this stuff out row-at-a-time for
   // interlaced files.
-  png_bytep *rows = (png_bytep *)PANDA_MALLOC_ARRAY(num_rows * sizeof(png_bytep));
+  png_bytep *rows = (png_bytep *)alloca(num_rows * sizeof(png_bytep));
   int yi;
 
+  png_byte *alloc = (png_byte *)PANDA_MALLOC_ARRAY(row_byte_length * sizeof(png_byte) * num_rows);
   for (yi = 0; yi < num_rows; yi++) {
-    rows[yi] = (png_byte *)PANDA_MALLOC_ARRAY(row_byte_length * sizeof(png_byte));
+    rows[yi] = alloc + (row_byte_length * sizeof(png_byte)) * yi;
   }
 
   png_read_image(_png, rows);
@@ -402,12 +403,10 @@ read_data(xel *array, xelval *alpha_data) {
     }
 
     nassertr(source <= rows[yi] + row_byte_length, yi);
-    PANDA_FREE_ARRAY(rows[yi]);
   }
 
-  PANDA_FREE_ARRAY(rows);
-
   png_read_end(_png, nullptr);
+  PANDA_FREE_ARRAY(alloc);
 
   return _y_size;
 }

Original file line number	Diff line number	Diff line change
`@@ -338,11 +338,12 @@ read_data(xel array, xelval alpha_data) {`
`338`	`338`	`// format, mainly because we keep array and alpha data separately, and there`
`339`	`339`	`// doesn't appear to be good support to get this stuff out row-at-a-time for`
`340`	`340`	`// interlaced files.`
`341`		`- png_bytep rows = (png_bytep )PANDA_MALLOC_ARRAY(num_rows * sizeof(png_bytep));`
	`341`	`+ png_bytep rows = (png_bytep )alloca(num_rows * sizeof(png_bytep));`
`342`	`342`	`int yi;`
`343`	`343`
	`344`	`+ png_byte alloc = (png_byte )PANDA_MALLOC_ARRAY(row_byte_length * sizeof(png_byte) * num_rows);`
`344`	`345`	`for (yi = 0; yi < num_rows; yi++) {`
`345`		`- rows[yi] = (png_byte )PANDA_MALLOC_ARRAY(row_byte_length sizeof(png_byte));`
	`346`	`+ rows[yi] = alloc + (row_byte_length * sizeof(png_byte)) * yi;`
`346`	`347`	`}`
`347`	`348`
`348`	`349`	`png_read_image(_png, rows);`
`@@ -402,12 +403,10 @@ read_data(xel array, xelval alpha_data) {`
`402`	`403`	`}`
`403`	`404`
`404`	`405`	`nassertr(source <= rows[yi] + row_byte_length, yi);`
`405`		`- PANDA_FREE_ARRAY(rows[yi]);`
`406`	`406`	`}`
`407`	`407`
`408`		`- PANDA_FREE_ARRAY(rows);`
`409`		`-`
`410`	`408`	`png_read_end(_png, nullptr);`
	`409`	`+ PANDA_FREE_ARRAY(alloc);`
`411`	`410`
`412`	`411`	`return _y_size;`
`413`	`412`	`}`