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https://github.com/nzbget/nzbget.git
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#454: one-pass simd decoder
updated SIMD decoder, support for end-of-stream detection
This commit is contained in:
Andrey Prygunkov
@@ -30,200 +30,20 @@
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namespace YEncode
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{
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namespace Sse2
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{
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#ifdef __SSE2__
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// combine two 8-bit ints into a 16-bit one
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#define UINT16_PACK(a, b) ((a) | ((b) << 8))
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#define XMM_SIZE 16 /*== (signed int)sizeof(__m128i)*/
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#define STOREU_XMM(dest, xmm) \
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_mm_storeu_si128((__m128i*)(dest), xmm)
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#define LOAD_HALVES(a, b) _mm_castps_si128(_mm_loadh_pi( \
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_mm_castsi128_ps(_mm_loadl_epi64((__m128i*)(a))), \
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(b) \
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))
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uint8_t eqFixLUT[256];
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alignas(32) __m64 eqAddLUT[256];
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size_t do_decode_sse2(const unsigned char* src, unsigned char* dest, size_t len, char* state) {
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if(len <= sizeof(__m128i)*2) return decode_scalar(src, dest, len, state);
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unsigned char *p = dest; // destination pointer
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unsigned long i = 0; // input position
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unsigned char escFirst = 0; // input character; first char needs escaping
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unsigned int nextMask = 0;
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char tState = 0;
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char* pState = state ? state : &tState;
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if((uintptr_t)src & ((sizeof(__m128i)-1))) {
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// find source memory alignment
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unsigned char* aSrc = (unsigned char*)(((uintptr_t)src + (sizeof(__m128i)-1)) & ~(sizeof(__m128i)-1));
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i = (unsigned long)(aSrc - src);
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p += decode_scalar(src, dest, i, pState);
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}
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if(*pState == 0 && i+1 < len && src[i] == '.')
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nextMask = 1;
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else if(*pState == 2 && i+2 < len && *(uint16_t*)(src + i) == UINT16_PACK('\n','.'))
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nextMask = 2;
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escFirst = *pState == 1;
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if(i + (sizeof(__m128i)+1) < len) {
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// our algorithm may perform an aligned load on the next part, of which we consider 2 bytes (for \r\n. sequence checking)
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size_t dLen = len - (sizeof(__m128i)+1);
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dLen = ((dLen-i) + 0xf) & ~0xf;
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unsigned char* dSrc = (unsigned char*)src + dLen + i;
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long dI = -(long)dLen;
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i += dLen;
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for(; dI; dI += sizeof(__m128i)) {
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__m128i data = _mm_load_si128((__m128i *)(dSrc + dI));
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// search for special chars
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__m128i cmpEq = _mm_cmpeq_epi8(data, _mm_set1_epi8('=')),
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cmp = _mm_or_si128(
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_mm_or_si128(
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_mm_cmpeq_epi8(data, _mm_set1_epi16(0x0a0d)), // \r\n
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_mm_cmpeq_epi8(data, _mm_set1_epi16(0x0d0a)) // \n\r
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),
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cmpEq
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);
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unsigned int mask = _mm_movemask_epi8(cmp); // not the most accurate mask if we have invalid sequences; we fix this up later
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__m128i oData;
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if(escFirst) { // rarely hit branch: seems to be faster to use 'if' than a lookup table, possibly due to values being able to be held in registers?
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// first byte needs escaping due to preceeding = in last loop iteration
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oData = _mm_sub_epi8(data, _mm_set_epi8(42,42,42,42,42,42,42,42,42,42,42,42,42,42,42,42+64));
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} else {
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oData = _mm_sub_epi8(data, _mm_set1_epi8(42));
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}
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mask &= ~escFirst;
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mask |= nextMask;
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if (mask != 0) {
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// a spec compliant encoder should never generate sequences: ==, =\n and =\r, but we'll handle them to be spec compliant
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// the yEnc specification requires any character following = to be unescaped, not skipped over, so we'll deal with that
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// firstly, resolve invalid sequences of = to deal with cases like '===='
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unsigned int maskEq = _mm_movemask_epi8(cmpEq);
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unsigned int tmp = eqFixLUT[(maskEq&0xff) & ~escFirst];
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maskEq = (eqFixLUT[(maskEq>>8) & ~(tmp>>7)] << 8) | tmp;
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escFirst = (maskEq >> (sizeof(__m128i)-1));
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// next, eliminate anything following a `=` from the special char mask; this eliminates cases of `=\r` so that they aren't removed
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maskEq <<= 1;
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mask &= ~maskEq;
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// unescape chars following `=`
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oData = _mm_add_epi8(
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oData,
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LOAD_HALVES(
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eqAddLUT + (maskEq&0xff),
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eqAddLUT + ((maskEq>>8)&0xff)
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)
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);
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// handle \r\n. sequences
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// RFC3977 requires the first dot on a line to be stripped, due to dot-stuffing
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// find instances of \r\n
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__m128i tmpData1, tmpData2;
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tmpData1 = _mm_insert_epi16(_mm_srli_si128(data, 1), *(uint16_t*)(dSrc + dI + sizeof(__m128i)-1), 7);
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tmpData2 = _mm_insert_epi16(_mm_srli_si128(data, 2), *(uint16_t*)(dSrc + dI + sizeof(__m128i)), 7);
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__m128i cmp1 = _mm_cmpeq_epi16(data, _mm_set1_epi16(0x0a0d));
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__m128i cmp2 = _mm_cmpeq_epi16(tmpData1, _mm_set1_epi16(0x0a0d));
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// prepare to merge the two comparisons
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cmp1 = _mm_srli_si128(cmp1, 1);
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// find all instances of .
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tmpData2 = _mm_cmpeq_epi8(tmpData2, _mm_set1_epi8('.'));
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// merge matches of \r\n with those for .
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unsigned int killDots = _mm_movemask_epi8(
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_mm_and_si128(tmpData2, _mm_or_si128(cmp1, cmp2))
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);
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mask |= (killDots << 2) & 0xffff;
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nextMask = killDots >> (sizeof(__m128i)-2);
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// all that's left is to 'compress' the data (skip over masked chars)
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alignas(32) uint32_t mmTmp[4];
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_mm_store_si128((__m128i*)mmTmp, oData);
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for(int j=0; j<4; j++) {
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if(mask & 0xf) {
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unsigned char* pMmTmp = (unsigned char*)(mmTmp + j);
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unsigned int maskn = ~mask;
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*p = pMmTmp[0];
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p += (maskn & 1);
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*p = pMmTmp[1];
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p += (maskn & 2) >> 1;
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*p = pMmTmp[2];
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p += (maskn & 4) >> 2;
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*p = pMmTmp[3];
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p += (maskn & 8) >> 3;
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} else {
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*(uint32_t*)p = mmTmp[j];
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p += 4;
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}
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mask >>= 4;
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}
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} else {
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STOREU_XMM(p, oData);
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p += XMM_SIZE;
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escFirst = 0;
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nextMask = 0;
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}
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}
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if(escFirst) *pState = 1; // escape next character
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else if(nextMask == 1) *pState = 0; // next character is '.', where previous two were \r\n
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else if(nextMask == 2) *pState = 2; // next characters are '\n.', previous is \r
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else *pState = 3;
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}
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// end alignment
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if(i < len) {
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p += decode_scalar(src + i, p, len - i, pState);
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}
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return p - dest;
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}
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extern size_t (*decode_sse2)(const unsigned char* src, unsigned char* dest, size_t len, char* state);
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#define SIMD_DECODER
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#include "SimdDecoder.cpp"
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#endif
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}
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void init_decode_sse2() {
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#ifdef __SSE2__
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decode_sse2 = &do_decode_sse2;
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// generate unshuf LUT
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for(int i=0; i<256; i++) {
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int k = i;
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uint8_t res[8];
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int p = 0;
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// fix LUT
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k = i;
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p = 0;
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for(int j=0; j<8; j++) {
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k = i >> j;
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if(k & 1) {
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p |= 1 << j;
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j++;
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}
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}
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eqFixLUT[i] = p;
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// sub LUT
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k = i;
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for(int j=0; j<8; j++) {
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res[j] = (k & 1) ? 192 /* == -64 */ : 0;
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k >>= 1;
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}
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_mm_storel_epi64((__m128i*)(eqAddLUT + i), _mm_loadl_epi64((__m128i*)res));
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}
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decode = &YEncode::Sse2::do_decode_simd<sizeof(__m128i), YEncode::Sse2::do_decode_sse<false>>;
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YEncode::Sse2::decoder_init();
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decode_simd = true;
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#endif
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}
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