Bug 815473 - Replace runtime computed jpeg_nbits_table by constants. r=jlebar

media/libjpeg/MOZCHANGES

@@ -44,7 +44,7 @@ To upgrade to a new revision of libjpeg-turbo, do the following:
 * Restore files modified in the Mozilla repository.
 
     $ hg revert --no-backup config.h jconfig.h Makefile.in MOZCHANGES \
-      mozilla.diff simd/Makefile.in
+      mozilla.diff simd/Makefile.in genTables.py
 
 * Update config.h and jconfig.h as noted previously.
 
@@ -58,6 +58,11 @@ To upgrade to a new revision of libjpeg-turbo, do the following:
 
     $ hg addremove
 
+== December 12, 2012 ==
+
+* Replace the runtime computed jpeg_nbits_table with constants in
+  jpeg_nbits_table.h to make it shareable among processes. (bug 815473)
+
 == October 13, 2012 ==
 
 * Modified config.h to use MOZ_ALWAYS_INLINE (bug 800106).

media/libjpeg/Makefile.in

@@ -163,3 +163,9 @@ EXPORTS	= \
 FORCE_STATIC_LIB = 1
 
 include $(topsrcdir)/config/rules.mk
+
+.PHONY: CONSTANT_TABLES
+CONSTANT_TABLES:
+	$(PYTHON) $(srcdir)/genTables.py
+
+jchuff.$(OBJ_SUFFIX): CONSTANT_TABLES

media/libjpeg/genTables.py

@@ -0,0 +1,16 @@
+#!/usr/bin/python
+
+import math
+
+f = open("jpeg_nbits_table.h", "w")
+
+for i in range(65536):
+    f.write('%2d' % math.ceil(math.log(i + 1, 2)))
+    if i != 65535:
+        f.write(',')
+    if (i + 1) % 16 == 0:
+        f.write('\n')
+    else:
+        f.write(' ')
+
+f.close()

media/libjpeg/jchuff.c

@@ -21,8 +21,10 @@
 #include "jchuff.h"		/* Declarations shared with jcphuff.c */
 #include <limits.h>
 
-static unsigned char jpeg_nbits_table[65536];
-static int jpeg_nbits_table_init = 0;
+static const unsigned char jpeg_nbits_table[65536] = {
+/* Number i needs jpeg_nbits_table[i] bits to be represented. */
+#include "jpeg_nbits_table.h"
+};
 
 #ifndef min
  #define min(a,b) ((a)<(b)?(a):(b))
@@ -270,15 +272,6 @@ jpeg_make_c_derived_tbl (j_compress_ptr cinfo, boolean isDC, int tblno,
     dtbl->ehufco[i] = huffcode[p];
     dtbl->ehufsi[i] = huffsize[p];
   }
-
-  if(!jpeg_nbits_table_init) {
-    for(i = 0; i < 65536; i++) {
-      int nbits = 0, temp = i;
-      while (temp) {temp >>= 1;  nbits++;}
-      jpeg_nbits_table[i] = nbits;
-    }
-    jpeg_nbits_table_init = 1;
-  }
 }
 
 

media/libjpeg/mozilla.diff

@@ -68,3 +68,54 @@
   * can change this datatype.
   */
  
+--- jchuff.c
++++ jchuff.c
+@@ -16,18 +16,20 @@
+  */
+ 
+ #define JPEG_INTERNALS
+ #include "jinclude.h"
+ #include "jpeglib.h"
+ #include "jchuff.h"		/* Declarations shared with jcphuff.c */
+ #include <limits.h>
+ 
+-static unsigned char jpeg_nbits_table[65536];
+-static int jpeg_nbits_table_init = 0;
++static const unsigned char jpeg_nbits_table[65536] = {
++/* Number i needs jpeg_nbits_table[i] bits to be represented. */
++#include "jpeg_nbits_table.h"
++};
+ 
+ #ifndef min
+  #define min(a,b) ((a)<(b)?(a):(b))
+ #endif
+ 
+ 
+ /* Expanded entropy encoder object for Huffman encoding.
+  *
+@@ -265,25 +267,16 @@ jpeg_make_c_derived_tbl (j_compress_ptr 
+ 
+   for (p = 0; p < lastp; p++) {
+     i = htbl->huffval[p];
+     if (i < 0 || i > maxsymbol || dtbl->ehufsi[i])
+       ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
+     dtbl->ehufco[i] = huffcode[p];
+     dtbl->ehufsi[i] = huffsize[p];
+   }
+-
+-  if(!jpeg_nbits_table_init) {
+-    for(i = 0; i < 65536; i++) {
+-      int nbits = 0, temp = i;
+-      while (temp) {temp >>= 1;  nbits++;}
+-      jpeg_nbits_table[i] = nbits;
+-    }
+-    jpeg_nbits_table_init = 1;
+-  }
+ }
+ 
+ 
+ /* Outputting bytes to the file */
+ 
+ /* Emit a byte, taking 'action' if must suspend. */
+ #define emit_byte(state,val,action)  \
+ 	{ *(state)->next_output_byte++ = (JOCTET) (val);  \