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* High quality image resampling with polyphase filters
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* Copyright (c) 2001 Fabrice Bellard
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* This file is part of FFmpeg.
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* FFmpeg is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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* FFmpeg is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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* You should have received a copy of the GNU Lesser General Public
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* License along with FFmpeg; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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* @file libavcodec/ppc/imgresample_altivec.c
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* High quality image resampling with polyphase filters - AltiVec bits
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#include "util_altivec.h"
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vector signed short v;
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void v_resample16_altivec(uint8_t *dst, int dst_width, const uint8_t *src,
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int wrap, int16_t *filter)
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vector unsigned char *tv, tmp, dstv, zero;
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vec_ss srchv[4], srclv[4], fv[4];
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vector signed short zeros, sumhv, sumlv;
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The vec_madds later on does an implicit >>15 on the result.
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Since FILTER_BITS is 8, and we have 15 bits of magnitude in
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a signed short, we have just enough bits to pre-shift our
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filter constants <<7 to compensate for vec_madds.
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fv[i].s[0] = filter[i] << (15-FILTER_BITS);
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fv[i].v = vec_splat(fv[i].v, 0);
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zero = vec_splat_u8(0);
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zeros = vec_splat_s16(0);
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When we're resampling, we'd ideally like both our input buffers,
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and output buffers to be 16-byte aligned, so we can do both aligned
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reads and writes. Sadly we can't always have this at the moment, so
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we opt for aligned writes, as unaligned writes have a huge overhead.
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To do this, do enough scalar resamples to get dst 16-byte aligned.
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i = (-(int)dst) & 0xf;
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sum = s[0 * wrap] * filter[0] +
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s[1 * wrap] * filter[1] +
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s[2 * wrap] * filter[2] +
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s[3 * wrap] * filter[3];
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sum = sum >> FILTER_BITS;
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if (sum<0) sum = 0; else if (sum>255) sum=255;
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/* Do our altivec resampling on 16 pixels at once. */
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while(dst_width>=16) {
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/* Read 16 (potentially unaligned) bytes from each of
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4 lines into 4 vectors, and split them into shorts.
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Interleave the multipy/accumulate for the resample
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filter with the loads to hide the 3 cycle latency
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the vec_madds have. */
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tv = (vector unsigned char *) &s[0 * wrap];
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tmp = vec_perm(tv[0], tv[1], vec_lvsl(0, &s[i * wrap]));
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srchv[0].v = (vector signed short) vec_mergeh(zero, tmp);
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srclv[0].v = (vector signed short) vec_mergel(zero, tmp);
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sumhv = vec_madds(srchv[0].v, fv[0].v, zeros);
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sumlv = vec_madds(srclv[0].v, fv[0].v, zeros);
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tv = (vector unsigned char *) &s[1 * wrap];
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tmp = vec_perm(tv[0], tv[1], vec_lvsl(0, &s[1 * wrap]));
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srchv[1].v = (vector signed short) vec_mergeh(zero, tmp);
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srclv[1].v = (vector signed short) vec_mergel(zero, tmp);
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sumhv = vec_madds(srchv[1].v, fv[1].v, sumhv);
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sumlv = vec_madds(srclv[1].v, fv[1].v, sumlv);
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tv = (vector unsigned char *) &s[2 * wrap];
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tmp = vec_perm(tv[0], tv[1], vec_lvsl(0, &s[2 * wrap]));
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srchv[2].v = (vector signed short) vec_mergeh(zero, tmp);
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srclv[2].v = (vector signed short) vec_mergel(zero, tmp);
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sumhv = vec_madds(srchv[2].v, fv[2].v, sumhv);
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sumlv = vec_madds(srclv[2].v, fv[2].v, sumlv);
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tv = (vector unsigned char *) &s[3 * wrap];
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tmp = vec_perm(tv[0], tv[1], vec_lvsl(0, &s[3 * wrap]));
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srchv[3].v = (vector signed short) vec_mergeh(zero, tmp);
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srclv[3].v = (vector signed short) vec_mergel(zero, tmp);
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sumhv = vec_madds(srchv[3].v, fv[3].v, sumhv);
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sumlv = vec_madds(srclv[3].v, fv[3].v, sumlv);
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/* Pack the results into our destination vector,
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and do an aligned write of that back to memory. */
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dstv = vec_packsu(sumhv, sumlv) ;
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vec_st(dstv, 0, (vector unsigned char *) dst);
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/* If there are any leftover pixels, resample them
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with the slow scalar method. */
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sum = s[0 * wrap] * filter[0] +
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s[1 * wrap] * filter[1] +
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s[2 * wrap] * filter[2] +
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s[3 * wrap] * filter[3];
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sum = sum >> FILTER_BITS;
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if (sum<0) sum = 0; else if (sum>255) sum=255;