Fixes issue #6071.

Corrects readBlockTiff() case for 1-bit depth and 1 color TIFF images incorporated in the PDF.

Adds reference test for PDF used to fix this issue.

src/core/stream.js

@@ -739,15 +739,16 @@ var PredictorStream = (function PredictorStreamClosure() {
     var pos = bufferLength;
     var i;
 
-    if (bits === 1) {
+    if (bits === 1 && colors === 1) {
+      // Optimized version of the loop in the "else"-branch
+      // for 1 bit-per-component and 1 color TIFF images.
       for (i = 0; i < rowBytes; ++i) {
-        var c = rawBytes[i];
-        inbuf = (inbuf << 8) | c;
-        // bitwise addition is exclusive or
-        // first shift inbuf and then add
-        buffer[pos++] = (c ^ (inbuf >> colors)) & 0xFF;
-        // truncate inbuf (assumes colors < 16)
-        inbuf &= 0xFFFF;
+        var c = rawBytes[i] ^ inbuf;
+        c ^= c >> 1;
+        c ^= c >> 2;
+        c ^= c >> 4;
+        inbuf = (c & 1) << 7;
+        buffer[pos++] = c;
       }
     } else if (bits === 8) {
       for (i = 0; i < colors; ++i) {

test/pdfs/issue6071.pdf.link

@@ -0,0 +1 @@
+https://web.archive.org/web/20170107214304/https://www.pdf-archive.com/2017/01/07/issue6071/issue6071.pdf

test/test_manifest.json

@@ -1146,6 +1146,13 @@
        "lastPage": 2,
        "type": "eq"
     },
+    {  "id": "issue6071",
+       "file": "pdfs/issue6071.pdf",
+       "md5": "2e08526d8e7c9ba4269fc12ef488d3eb",
+       "rounds": 1,
+       "link": true,
+       "type": "eq"
+    },
     {  "id": "issue1905",
        "file": "pdfs/issue1905.pdf",
        "md5": "b1bbd72ca6522ae1502aa26320f81994",