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simplify VP8LInitBitReader()

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gcc was generating very complex code, one for each case of br->len_ values!

also, pretty-fy the mask constants

Change-Id: If62b1e8266f3fe5334517305113038d2ea8a6b42
This commit is contained in:
Pascal Massimino 2014-05-22 21:38:53 -07:00
parent 515e35cfb1
commit fdbcd44dd3
1 changed files with 18 additions and 9 deletions
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27
src/utils/bit_reader.c
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@ -121,29 +121,38 @@ int32_t VP8GetSignedValue(VP8BitReader* const br, int bits) {
#define LOG8_WBITS 4 // Number of bytes needed to store WBITS bits.
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
0,
0x000001, 0x000003, 0x000007, 0x00000f,
0x00001f, 0x00003f, 0x00007f, 0x0000ff,
0x0001ff, 0x0003ff, 0x0007ff, 0x000fff,
0x001fff, 0x003fff, 0x007fff, 0x00ffff,
0x01ffff, 0x03ffff, 0x07ffff, 0x0fffff,
0x1fffff, 0x3fffff, 0x7fffff, 0xffffff
};
void VP8LInitBitReader(VP8LBitReader* const br,
const uint8_t* const start,
void VP8LInitBitReader(VP8LBitReader* const br, const uint8_t* const start,
size_t length) {
size_t i;
vp8l_val_t value = 0;
assert(br != NULL);
assert(start != NULL);
assert(length < 0xfffffff8u); // can't happen with a RIFF chunk.
br->buf_ = start;
br->len_ = length;
br->val_ = 0;
br->pos_ = 0;
br->bit_pos_ = 0;
br->eos_ = 0;
br->error_ = 0;
for (i = 0; i < sizeof(br->val_) && i < br->len_; ++i) {
br->val_ |= ((vp8l_val_t)br->buf_[br->pos_]) << (8 * i);
++br->pos_;
if (length > sizeof(br->val_)) {
length = sizeof(br->val_);
}
for (i = 0; i < length; ++i) {
value |= (vp8l_val_t)start[i] << (8 * i);
}
br->val_ = value;
br->pos_ = length;
br->buf_ = start;
}
// Special version that assumes br->pos_ <= br_len_.