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--- jcdctmgr.c.orig 2015-05-18 14:28:09 UTC
+++ jcdctmgr.c
@@ -6,7 +6,7 @@
* libjpeg-turbo Modifications:
* Copyright (C) 1999-2006, MIYASAKA Masaru.
* Copyright 2009 Pierre Ossman <ossman@cendio.se> for Cendio AB
- * Copyright (C) 2011, 2014 D. R. Commander
+ * Copyright (C) 2011, 2014-2015 D. R. Commander
* mozjpeg Modifications:
* Copyright (C) 2014, Mozilla Corporation.
* For conditions of distribution and use, see the accompanying README file.
@@ -185,6 +185,19 @@ compute_reciprocal (UINT16 divisor, DCTE
UDCTELEM c;
int b, r;
+ if (divisor == 1) {
+ /* divisor == 1 means unquantized, so these reciprocal/correction/shift
+ * values will cause the C quantization algorithm to act like the
+ * identity function. Since only the C quantization algorithm is used in
+ * these cases, the scale value is irrelevant.
+ */
+ dtbl[DCTSIZE2 * 0] = (DCTELEM) 1; /* reciprocal */
+ dtbl[DCTSIZE2 * 1] = (DCTELEM) 0; /* correction */
+ dtbl[DCTSIZE2 * 2] = (DCTELEM) 1; /* scale */
+ dtbl[DCTSIZE2 * 3] = (DCTELEM) (-sizeof(DCTELEM) * 8); /* shift */
+ return 0;
+ }
+
b = flss(divisor) - 1;
r = sizeof(DCTELEM) * 8 + b;
@@ -589,7 +602,8 @@ quantize (JCOEFPTR coef_block, DCTELEM *
#if BITS_IN_JSAMPLE == 8
- UDCTELEM recip, corr, shift;
+ UDCTELEM recip, corr;
+ int shift;
UDCTELEM2 product;
for (i = 0; i < DCTSIZE2; i++) {
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