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ARM: speed up bitreader by avoiding tables

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(and using BitsLog2Floor() from utils.h instead)

9-10% speed-up, apparently

Change-Id: I9acae4a4dceb1ddcc99306f99b722079bb06f6f8
This commit is contained in:
Pascal Massimino 2017-01-17 23:52:37 -08:00
parent 1dc82a6bba
commit a345068aba
1 changed files with 8 additions and 20 deletions
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28
src/utils/bit_reader_inl.h
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@ -116,31 +116,19 @@ static WEBP_INLINE int VP8GetBit(VP8BitReader* const br, int prob) {
const int pos = br->bits_;
const range_t split = (range * prob) >> 8;
const range_t value = (range_t)(br->value_ >> pos);
#if defined(__arm__) || defined(_M_ARM) // ARM-specific
const int bit = ((int)(split - value) >> 31) & 1;
if (value > split) {
range -= split + 1;
const int bit = (value > split);
if (bit) {
range -= split;
br->value_ -= (bit_t)(split + 1) << pos;
} else {
range = split;
range = split + 1;
}
#else // faster version on x86
int bit; // Don't use 'const int bit = (value > split);", it's slower.
if (value > split) {
range -= split + 1;
br->value_ -= (bit_t)(split + 1) << pos;
bit = 1;
} else {
range = split;
bit = 0;
}
#endif
if (range <= (range_t)0x7e) {
const int shift = kVP8Log2Range[range];
range = kVP8NewRange[range];
{
const int shift = 7 ^ BitsLog2Floor(range);
range <<= shift;
br->bits_ -= shift;
}
br->range_ = range;
br->range_ = range - 1;
return bit;
}
}