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Bug 1050342. Fix a case where the fast huffman decoder in libjpeg-turbo can produce different results depending on how data is fed to it.
This change comes from the blink repo https://codereview.appspot.com/229430043/ and is unlikely to be accepted upstream into libjpeg-turbo.
diff --git jdhuff.c jdhuff.c
--- jdhuff.c
+++ jdhuff.c
@@ -664,17 +664,17 @@ decode_mcu_fast (j_decompress_ptr cinfo,
ASSIGN_STATE(state, entropy->saved);
for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
JBLOCKROW block = MCU_data ? MCU_data[blkn] : NULL;
d_derived_tbl *dctbl = entropy->dc_cur_tbls[blkn];
d_derived_tbl *actbl = entropy->ac_cur_tbls[blkn];
register int s, k, r, l;
- HUFF_DECODE_FAST(s, l, dctbl);
+ HUFF_DECODE_FAST(s, l, dctbl, slow_decode_mcu);
if (s) {
FILL_BIT_BUFFER_FAST
r = GET_BITS(s);
s = HUFF_EXTEND(r, s);
}
if (entropy->dc_needed[blkn]) {
int ci = cinfo->MCU_membership[blkn];
@@ -682,17 +682,17 @@ decode_mcu_fast (j_decompress_ptr cinfo,
state.last_dc_val[ci] = s;
if (block)
(*block)[0] = (JCOEF) s;
}
if (entropy->ac_needed[blkn] && block) {
for (k = 1; k < DCTSIZE2; k++) {
- HUFF_DECODE_FAST(s, l, actbl);
+ HUFF_DECODE_FAST(s, l, actbl, slow_decode_mcu);
r = s >> 4;
s &= 15;
if (s) {
k += r;
FILL_BIT_BUFFER_FAST
r = GET_BITS(s);
s = HUFF_EXTEND(r, s);
@@ -701,33 +701,34 @@ decode_mcu_fast (j_decompress_ptr cinfo,
if (r != 15) break;
k += 15;
}
}
} else {
for (k = 1; k < DCTSIZE2; k++) {
- HUFF_DECODE_FAST(s, l, actbl);
+ HUFF_DECODE_FAST(s, l, actbl, slow_decode_mcu);
r = s >> 4;
s &= 15;
if (s) {
k += r;
FILL_BIT_BUFFER_FAST
DROP_BITS(s);
} else {
if (r != 15) break;
k += 15;
}
}
}
}
if (cinfo->unread_marker != 0) {
+slow_decode_mcu:
cinfo->unread_marker = 0;
return FALSE;
}
br_state.bytes_in_buffer -= (buffer - br_state.next_input_byte);
br_state.next_input_byte = buffer;
BITREAD_SAVE_STATE(cinfo,entropy->bitstate);
ASSIGN_STATE(entropy->saved, state);
diff --git jdhuff.h jdhuff.h
--- jdhuff.h
+++ jdhuff.h
@@ -203,32 +203,34 @@ EXTERN(boolean) jpeg_fill_bit_buffer
} else { \
slowlabel: \
if ((result=jpeg_huff_decode(&state,get_buffer,bits_left,htbl,nb)) < 0) \
{ failaction; } \
get_buffer = state.get_buffer; bits_left = state.bits_left; \
} \
}
-#define HUFF_DECODE_FAST(s,nb,htbl) \
+#define HUFF_DECODE_FAST(s,nb,htbl,slowlabel) \
FILL_BIT_BUFFER_FAST; \
s = PEEK_BITS(HUFF_LOOKAHEAD); \
s = htbl->lookup[s]; \
nb = s >> HUFF_LOOKAHEAD; \
/* Pre-execute the common case of nb <= HUFF_LOOKAHEAD */ \
DROP_BITS(nb); \
s = s & ((1 << HUFF_LOOKAHEAD) - 1); \
if (nb > HUFF_LOOKAHEAD) { \
/* Equivalent of jpeg_huff_decode() */ \
/* Don't use GET_BITS() here because we don't want to modify bits_left */ \
s = (get_buffer >> bits_left) & ((1 << (nb)) - 1); \
while (s > htbl->maxcode[nb]) { \
s <<= 1; \
s |= GET_BITS(1); \
nb++; \
} \
- s = htbl->pub->huffval[ (int) (s + htbl->valoffset[nb]) & 0xFF ]; \
+ if (nb > 16) \
+ goto slowlabel; \
+ s = htbl->pub->huffval[ (int) (s + htbl->valoffset[nb]) ]; \
}
/* Out-of-line case for Huffman code fetching */
EXTERN(int) jpeg_huff_decode
(bitread_working_state *state, register bit_buf_type get_buffer,
register int bits_left, d_derived_tbl *htbl, int min_bits);
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