mirror of https://github.com/FreeRDP/FreeRDP
codec: fixed and accelerated RemoteFX ycbcr-to-rgb decoder
The current ycbcr decoder was loosing some bits because cr/cb was multiplied by the shifted factors. Instead one should multiply by the non-shifted factors and shift the result. The effects of these lost bits are easily seen by comparing the colors of a RemoteFX session with the colors of a plain RDP session - they are just wrong ;) I've replaced the bit-magic from the non non-accelerated version (rfx_decode.c) and replaced it with simple float multiplications using the compiler's implicit integer conversions. On several test machines this was even a little bit faster. The accelerated SSE2 ycbcr decoder (rfx_sse2.c) was completely changed in order to make use of the SSE2 signed 16-bit integer multiplication. Fortunately the factors in the conversion matrix are so small that we can easily shift them to the maximum possible 16-bit signed integer value without loosing any information and use _mm_mulhi_epi16 which takes the upper 16 bits of the 32-bit result. The SSE2 ycbcr decoder is now much simpler and about 40 percent faster.
This commit is contained in:
Norbert Federa
parent
c5a2cf3035
commit
04518f0b42
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@ -98,19 +98,17 @@ void rfx_decode_ycbcr_to_rgb(sint16* y_r_buf, sint16* cb_g_buf, sint16* cr_b_buf
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*/
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for (i = 0; i < 4096; i++)
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{
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y = (y_r_buf[i] >> 5) + 128;
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y = y_r_buf[i] + 4096; // 128<<5 = 4096 so that we can >> 5 over the sum
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cb = cb_g_buf[i];
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cr = cr_b_buf[i];
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/* 1.403 >> 5 = 0.000010110011100(b) */
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r = y + ((cr >> 5) + (cr >> 7) + (cr >> 8) + (cr >> 11) + (cr >> 12) + (cr >> 13));
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y_r_buf[i] = MINMAX(r, 0, 255);
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/* 0.344 >> 5 = 0.000000101100000(b), 0.714 >> 5 = 0.000001011011011(b) */
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g = y - ((cb >> 7) + (cb >> 9) + (cb >> 10)) -
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((cr >> 6) + (cr >> 8) + (cr >> 9) + (cr >> 11) + (cr >> 12) + (cr >> 13));
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cb_g_buf[i] = MINMAX(g, 0, 255);
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/* 1.77 >> 5 = 0.000011100010100(b) */
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b = y + ((cb >> 5) + (cb >> 6) + (cb >> 7) + (cb >> 11) + (cb >> 13));
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cr_b_buf[i] = MINMAX(b, 0, 255);
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r = y + cr*1.403f;
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g = y - cb*0.344f - cr*0.714f;
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b = y + cb*1.770f;
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y_r_buf[i] = MINMAX(r>>5, 0, 255);
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cb_g_buf[i] = MINMAX(g>>5, 0, 255);
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cr_b_buf[i] = MINMAX(b>>5, 0, 255);
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}
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}
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@ -3,6 +3,7 @@
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* RemoteFX Codec Library - SSE2 Optimizations
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*
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* Copyright 2011 Stephen Erisman
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* Copyright 2011 Norbert Federa <nfedera@thinstuff.com>
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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@ -64,6 +65,12 @@ static void rfx_decode_ycbcr_to_rgb_sse2(sint16* y_r_buffer, sint16* cb_g_buffer
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int i;
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__m128i r_cr = _mm_set1_epi16(22986); // 1.403 << 14
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__m128i g_cb = _mm_set1_epi16(-5636); // -0.344 << 14
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__m128i g_cr = _mm_set1_epi16(-11698); // -0.714 << 14
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__m128i b_cb = _mm_set1_epi16(28999); // 1.770 << 14
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__m128i c4096 = _mm_set1_epi16(4096);
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for (i = 0; i < (4096 * sizeof(sint16) / sizeof(__m128i)); i += (CACHE_LINE_BYTES / sizeof(__m128i)))
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{
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_mm_prefetch((char*)(&y_r_buf[i]), _MM_HINT_NTA);
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@ -72,49 +79,51 @@ static void rfx_decode_ycbcr_to_rgb_sse2(sint16* y_r_buffer, sint16* cb_g_buffer
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}
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for (i = 0; i < (4096 * sizeof(sint16) / sizeof(__m128i)); i++)
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{
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/* y = (y_r_buf[i] >> 5) + 128; */
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y = _mm_load_si128(&y_r_buf[i]);
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y = _mm_add_epi16(_mm_srai_epi16(y, 5), _mm_set1_epi16(128));
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/*
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In order to use SSE2 signed 16-bit integer multiplication we need to convert
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the floating point factors to signed int without loosing information.
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The result of this multiplication is 32 bit and we have two SSE instructions
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that return either the hi or lo word.
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Thus we will multiply the factors by the highest possible 2^n, take the
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upper 16 bits of the signed 32-bit result (_mm_mulhi_epi16) and correct this
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result by multiplying it by 2^(16-n).
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For the given factors in the conversion matrix the best possible n is 14.
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Example for calculating r:
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r = (y>>5) + 128 + (cr*1.403)>>5 // our base formula
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r = (y>>5) + 128 + (HIWORD(cr*(1.403<<14)<<2))>>5 // see above
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r = (y+4096)>>5 + (HIWORD(cr*22986)<<2)>>5 // simplification
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r = ((y+4096)>>2 + HIWORD(cr*22986)) >> 3
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*/
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/* y = (y_r_buf[i] + 4096) >> 2 */
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y = _mm_load_si128(&y_r_buf[i]);
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y = _mm_add_epi16(y, c4096);
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y = _mm_srai_epi16(y, 2);
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/* cb = cb_g_buf[i]; */
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cb = _mm_load_si128(&cb_g_buf[i]);
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/* cr = cr_b_buf[i]; */
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cr = _mm_load_si128(&cr_b_buf[i]);
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/* r = y + ((cr >> 5) + (cr >> 7) + (cr >> 8) + (cr >> 11) + (cr >> 12) + (cr >> 13)); */
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/* (y + HIWORD(cr*22986)) >> 3 */
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r = _mm_add_epi16(y, _mm_mulhi_epi16(cr, r_cr));
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r = _mm_srai_epi16(r, 3);
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/* y_r_buf[i] = MINMAX(r, 0, 255); */
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r = _mm_add_epi16(y, _mm_srai_epi16(cr, 5));
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r = _mm_add_epi16(r, _mm_srai_epi16(cr, 7));
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r = _mm_add_epi16(r, _mm_srai_epi16(cr, 8));
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r = _mm_add_epi16(r, _mm_srai_epi16(cr, 11));
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r = _mm_add_epi16(r, _mm_srai_epi16(cr, 12));
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r = _mm_add_epi16(r, _mm_srai_epi16(cr, 13));
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_mm_between_epi16(r, zero, max);
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_mm_store_si128(&y_r_buf[i], r);
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/* cb = cb_g_buf[i]; */
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cb = _mm_load_si128(&cb_g_buf[i]);
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/* g = y - ((cb >> 7) + (cb >> 9) + (cb >> 10)) -
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((cr >> 6) + (cr >> 8) + (cr >> 9) + (cr >> 11) + (cr >> 12) + (cr >> 13)); */
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/* (y + HIWORD(cb*-5636) + HIWORD(cr*-11698)) >> 3 */
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g = _mm_add_epi16(y, _mm_mulhi_epi16(cb, g_cb));
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g = _mm_add_epi16(g, _mm_mulhi_epi16(cr, g_cr));
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g = _mm_srai_epi16(g, 3);
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/* cb_g_buf[i] = MINMAX(g, 0, 255); */
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g = _mm_sub_epi16(y, _mm_srai_epi16(cb, 7));
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g = _mm_sub_epi16(g, _mm_srai_epi16(cb, 9));
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g = _mm_sub_epi16(g, _mm_srai_epi16(cb, 10));
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g = _mm_sub_epi16(g, _mm_srai_epi16(cr, 6));
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g = _mm_sub_epi16(g, _mm_srai_epi16(cr, 8));
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g = _mm_sub_epi16(g, _mm_srai_epi16(cr, 9));
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g = _mm_sub_epi16(g, _mm_srai_epi16(cr, 11));
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g = _mm_sub_epi16(g, _mm_srai_epi16(cr, 12));
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g = _mm_sub_epi16(g, _mm_srai_epi16(cr, 13));
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_mm_between_epi16(g, zero, max);
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_mm_store_si128(&cb_g_buf[i], g);
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/* b = y + ((cb >> 5) + (cb >> 6) + (cb >> 7) + (cb >> 11) + (cb >> 13)); */
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/* (y + HIWORD(cb*28999)) >> 3 */
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b = _mm_add_epi16(y, _mm_mulhi_epi16(cb, b_cb));
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b = _mm_srai_epi16(b, 3);
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/* cr_b_buf[i] = MINMAX(b, 0, 255); */
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b = _mm_add_epi16(y, _mm_srai_epi16(cb, 5));
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b = _mm_add_epi16(b, _mm_srai_epi16(cb, 6));
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b = _mm_add_epi16(b, _mm_srai_epi16(cb, 7));
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b = _mm_add_epi16(b, _mm_srai_epi16(cb, 11));
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b = _mm_add_epi16(b, _mm_srai_epi16(cb, 13));
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_mm_between_epi16(b, zero, max);
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_mm_store_si128(&cr_b_buf[i], b);
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}
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