Integrate a slightly modified version of Mozilla's patch for precomputing the bit-counting LUT. This is useful if the table needs to be shared among multiple processes, although the primary reason for doing that is reduced footprint on mobile devices, which are probably already covered by the clz intrinsic code.

jchuff.c

@@ -47,8 +47,7 @@
 #define JPEG_NBITS_NONZERO(x) (32 - __builtin_clz(x))
 #define JPEG_NBITS(x) (x ? JPEG_NBITS_NONZERO(x) : 0)
 #else
-static unsigned char jpeg_nbits_table[65536];
-static int jpeg_nbits_table_init = 0;
+#include "jpeg_nbits_table.h"
 #define JPEG_NBITS(x) (jpeg_nbits_table[x])
 #define JPEG_NBITS_NONZERO(x) JPEG_NBITS(x)
 #endif
@@ -299,17 +298,6 @@ jpeg_make_c_derived_tbl (j_compress_ptr cinfo, boolean isDC, int tblno,
     dtbl->ehufco[i] = huffcode[p];
     dtbl->ehufsi[i] = huffsize[p];
   }
-
-#ifndef USE_CLZ_INTRINSIC
-  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;
-  }
-#endif
 }