diff options
Diffstat (limited to 'vp8/decoder/dboolhuff.h')
| -rw-r--r-- | vp8/decoder/dboolhuff.h | 50 |
1 files changed, 29 insertions, 21 deletions
diff --git a/vp8/decoder/dboolhuff.h b/vp8/decoder/dboolhuff.h index a83e3f012..5f6b211ea 100644 --- a/vp8/decoder/dboolhuff.h +++ b/vp8/decoder/dboolhuff.h @@ -51,19 +51,26 @@ void vp8dx_bool_decoder_fill(BOOL_DECODER *br); #define VP8DX_BOOL_DECODER_FILL(_count,_value,_bufptr,_bufend) \ do \ { \ - int shift; \ - for(shift = VP8_BD_VALUE_SIZE - 8 - ((_count) + 8); shift >= 0; ) \ + int shift = VP8_BD_VALUE_SIZE - 8 - ((_count) + 8); \ + int loop_end, x; \ + size_t bits_left = ((_bufend)-(_bufptr))*CHAR_BIT; \ + \ + x = shift + CHAR_BIT - bits_left; \ + loop_end = 0; \ + if(x >= 0) \ { \ - if((_bufptr) >= (_bufend)) { \ - (_count) = VP8_LOTS_OF_BITS; \ - break; \ - } \ - (_count) += 8; \ + (_count) += VP8_LOTS_OF_BITS; \ + loop_end = x; \ + if(!bits_left) break; \ + } \ + while(shift >= loop_end) \ + { \ + (_count) += CHAR_BIT; \ (_value) |= (VP8_BD_VALUE)*(_bufptr)++ << shift; \ - shift -= 8; \ + shift -= CHAR_BIT; \ } \ } \ - while(0) + while(0) \ static int vp8dx_decode_bool(BOOL_DECODER *br, int probability) { @@ -119,18 +126,19 @@ static int vp8_decode_value(BOOL_DECODER *br, int bits) static int vp8dx_bool_error(BOOL_DECODER *br) { - /* Check if we have reached the end of the buffer. - * - * Variable 'count' stores the number of bits in the 'value' buffer, - * minus 8. So if count == 8, there are 16 bits available to be read. - * Normally, count is filled with 8 and one byte is filled into the - * value buffer. When we reach the end of the buffer, count is instead - * filled with VP8_LOTS_OF_BITS, 8 of which represent the last 8 real - * bits from the bitstream. So the last bit in the bitstream will be - * represented by count == VP8_LOTS_OF_BITS - 16. - */ - if ((br->count > VP8_BD_VALUE_SIZE) - && (br->count <= VP8_LOTS_OF_BITS - 16)) + /* Check if we have reached the end of the buffer. + * + * Variable 'count' stores the number of bits in the 'value' buffer, minus + * 8. The top byte is part of the algorithm, and the remainder is buffered + * to be shifted into it. So if count == 8, the top 16 bits of 'value' are + * occupied, 8 for the algorithm and 8 in the buffer. + * + * When reading a byte from the user's buffer, count is filled with 8 and + * one byte is filled into the value buffer. When we reach the end of the + * data, count is additionally filled with VP8_LOTS_OF_BITS. So when + * count == VP8_LOTS_OF_BITS - 1, the user's data has been exhausted. + */ + if ((br->count > VP8_BD_VALUE_SIZE) && (br->count < VP8_LOTS_OF_BITS)) { /* We have tried to decode bits after the end of * stream was encountered. |