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fix the bit-writer for lossless in 32bit mode

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Sometimes, we can write 18bit or more at time, and it would
overflow the 32bit accumulator.

Also clarified the num-bits limitations (and exposed
VP8L_MAX_NUM_BIT_READ in bit_reader.h)

fixes http://code.google.com/p/webp/issues/detail?id=200

Seems a bit faster (use of local fields for bits_ / used_)

also: added the __QNX__ bswap while at it.

Change-Id: I876db93a931db15b083cf1d838c70105effa7167
This commit is contained in:
skal
2014-05-22 07:17:24 +02:00
parent 541784c710
commit 176fda2650
4 changed files with 50 additions and 23 deletions
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6
src/utils/bit_reader.c
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@ -116,13 +116,11 @@ int32_t VP8GetSignedValue(VP8BitReader* const br, int bits) {
//------------------------------------------------------------------------------
// VP8LBitReader
#define MAX_NUM_BIT_READ 25
#define LBITS 64 // Number of bits prefetched.
#define WBITS 32 // Minimum number of bytes needed after VP8LFillBitWindow.
#define LOG8_WBITS 4 // Number of bytes needed to store WBITS bits.
static const uint32_t kBitMask[MAX_NUM_BIT_READ] = {
static const uint32_t kBitMask[VP8L_MAX_NUM_BIT_READ + 1] = {
0, 1, 3, 7, 15, 31, 63, 127, 255, 511, 1023, 2047, 4095, 8191, 16383, 32767,
65535, 131071, 262143, 524287, 1048575, 2097151, 4194303, 8388607, 16777215
};
@ -199,7 +197,7 @@ void VP8LFillBitWindow(VP8LBitReader* const br) {
uint32_t VP8LReadBits(VP8LBitReader* const br, int n_bits) {
assert(n_bits >= 0);
// Flag an error if end_of_stream or n_bits is more than allowed limit.
if (!br->eos_ && n_bits < MAX_NUM_BIT_READ) {
if (!br->eos_ && n_bits <= VP8L_MAX_NUM_BIT_READ) {
const uint32_t val =
(uint32_t)(br->val_ >> br->bit_pos_) & kBitMask[n_bits];
const int new_bits = br->bit_pos_ + n_bits;