From 563b68e74d82fec352783f2b54dac90228b59a72 Mon Sep 17 00:00:00 2001
From: Jonas Jenwald <jonas.jenwald@gmail.com>
Date: Tue, 15 Aug 2017 16:45:33 +0200
Subject: [PATCH] Remove manual clamping code in `src/core/jpx.js`

Since we're now using `Uint8ClampedArray`, rather than `Uint8Array`, doing manual clamping shouldn't be necessary given that that is now handled natively.

This shouldn't have any measurable performance impact, but just to sanity check that I've done some quick benchmarking with the following manifest file:
```json
[
    {  "id": "S2-eq",
       "file": "pdfs/S2.pdf",
       "md5": "d0b6137846df6e0fe058f234a87fb588",
       "rounds": 100,
       "type": "eq"
    }
]
```
which gave the following results against the current `master` (repeated benchmark runs didn't result in any meaningful differences):
```
-- Grouped By browser, stat --
browser | stat         | Count | Baseline(ms) | Current(ms) | +/- |    %  | Result(P<.05)
------- | ------------ | ----- | ------------ | ----------- | --- | ----- | -------------
firefox | Overall      |   100 |          592 |         592 |   1 |  0.12 |
firefox | Page Request |   100 |            3 |           3 |   0 | -9.88 |
firefox | Rendering    |   100 |          588 |         589 |   1 |  0.18 |
```
---
 src/core/jpx.js | 36 ++++++++++++------------------------
 1 file changed, 12 insertions(+), 24 deletions(-)

diff --git a/src/core/jpx.js b/src/core/jpx.js
index 7d5490df1..7139d6602 100644
--- a/src/core/jpx.js
+++ b/src/core/jpx.js
@@ -1396,8 +1396,8 @@ var JpxImage = (function JpxImageClosure() {
       };
 
       // Section G.2.2 Inverse multi component transform
-      var shift, offset, max, min, maxK;
-      var pos = 0, j, jj, y0, y1, y2, r, g, b, k, val;
+      var shift, offset;
+      var pos = 0, j, jj, y0, y1, y2;
       if (tile.codingStyleDefaultParameters.multipleComponentTransform) {
         var fourComponents = componentsCount === 4;
         var y0items = transformedTiles[0].items;
@@ -1410,9 +1410,6 @@ var JpxImage = (function JpxImageClosure() {
         // compute shift and offset only once.
         shift = components[0].precision - 8;
         offset = (128 << shift) + 0.5;
-        max = 255 * (1 << shift);
-        maxK = max * 0.5;
-        min = -maxK;
 
         var component0 = tile.components[0];
         var alpha01 = componentsCount - 3;
@@ -1423,12 +1420,9 @@ var JpxImage = (function JpxImageClosure() {
             y0 = y0items[j] + offset;
             y1 = y1items[j];
             y2 = y2items[j];
-            r = y0 + 1.402 * y2;
-            g = y0 - 0.34413 * y1 - 0.71414 * y2;
-            b = y0 + 1.772 * y1;
-            out[pos++] = r <= 0 ? 0 : r >= max ? 255 : r >> shift;
-            out[pos++] = g <= 0 ? 0 : g >= max ? 255 : g >> shift;
-            out[pos++] = b <= 0 ? 0 : b >= max ? 255 : b >> shift;
+            out[pos++] = (y0 + 1.402 * y2) >> shift;
+            out[pos++] = (y0 - 0.34413 * y1 - 0.71414 * y2) >> shift;
+            out[pos++] = (y0 + 1.772 * y1) >> shift;
           }
         } else {
           // inverse reversible multiple component transform
@@ -1436,18 +1430,16 @@ var JpxImage = (function JpxImageClosure() {
             y0 = y0items[j] + offset;
             y1 = y1items[j];
             y2 = y2items[j];
-            g = y0 - ((y2 + y1) >> 2);
-            r = g + y2;
-            b = g + y1;
-            out[pos++] = r <= 0 ? 0 : r >= max ? 255 : r >> shift;
-            out[pos++] = g <= 0 ? 0 : g >= max ? 255 : g >> shift;
-            out[pos++] = b <= 0 ? 0 : b >= max ? 255 : b >> shift;
+            let g = y0 - ((y2 + y1) >> 2);
+
+            out[pos++] = (g + y2) >> shift;
+            out[pos++] = g >> shift;
+            out[pos++] = (g + y1) >> shift;
           }
         }
         if (fourComponents) {
           for (j = 0, pos = 3; j < jj; j++, pos += 4) {
-            k = y3items[j];
-            out[pos] = k <= min ? 0 : k >= maxK ? 255 : (k + offset) >> shift;
+            out[pos] = (y3items[j] + offset) >> shift;
           }
         }
       } else { // no multi-component transform
@@ -1455,12 +1447,8 @@ var JpxImage = (function JpxImageClosure() {
           var items = transformedTiles[c].items;
           shift = components[c].precision - 8;
           offset = (128 << shift) + 0.5;
-          max = (127.5 * (1 << shift));
-          min = -max;
           for (pos = c, j = 0, jj = items.length; j < jj; j++) {
-            val = items[j];
-            out[pos] = val <= min ? 0 :
-                       val >= max ? 255 : (val + offset) >> shift;
+            out[pos] = (items[j] + offset) >> shift;
             pos += componentsCount;
           }
         }