Performance pitfalls

git-svn-id: https://libjpeg-turbo.svn.sourceforge.net/svnroot/libjpeg-turbo@380 3789f03b-4d11-0410-bbf8-ca57d06f2519

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diff --git a/branches/1.1.x/README-turbo.txt b/branches/1.1.x/README-turbo.txt
index 9aa44ab..540da09 100755
--- a/branches/1.1.x/README-turbo.txt
+++ b/branches/1.1.x/README-turbo.txt
@@ -43,6 +43,34 @@ counterparts from the libjpeg v6b source.
 
 
 *******************************************************************************
+**     Performance pitfalls
+*******************************************************************************
+
+===============
+Restart Markers
+===============
+
+The optimized Huffman decoder in libjpeg-turbo does not handle restart markers
+in a way that makes libjpeg happy, so it is necessary to use the slow Huffman
+decoder when decompressing a JPEG image that has restart markers.  This can
+cause the decompression performance to drop by as much as 20%, but the
+performance will still be much much greater than that of libjpeg v6b.  Many
+consumer packages, such as PhotoShop, use restart markers when generating JPEG
+images, so images generated by those programs will experience this issue.
+
+===============================================
+Fast Forward Integer DCT at High Quality Levels
+===============================================
+
+The algorithm used by the SIMD-accelerated quantization function cannot produce
+correct results whenever the fast forward integer DCT is used along with a JPEG
+quality of 98-100.  Thus, libjpeg-turbo must use the non-SIMD quantization
+function in those cases.  This causes performance to drop by as much as 40%.
+It is therefore strongly advised that you use the slow forward integer DCT
+whenever encoding images with a JPEG quality of 98 or higher.
+
+
+*******************************************************************************
 **     Using libjpeg-turbo
 *******************************************************************************