text: // Copyright 2015 Google Inc. All Rights Reserved.
  //
  // Use of this source code is governed by a BSD-style license
  // that can be found in the COPYING file in the root of the source
  // tree. An additional intellectual property rights grant can be found
  // in the file PATENTS. All contributing project authors may
  // be found in the AUTHORS file in the root of the source tree.
  // -----------------------------------------------------------------------------
  //
  // Utilities for processing transparent channel, SSE4.1 variant.
  //
  // Author: Skal (pascal.massimino@gmail.com)
  
  #include "src/dsp/dsp.h"
  
  #if defined(WEBP_USE_SSE41)
  
  #include <smmintrin.h>
  
  //------------------------------------------------------------------------------
  
  static int ExtractAlpha_SSE41(const uint8_t* argb, int argb_stride,
                                int width, int height,
                                uint8_t* alpha, int alpha_stride) {
    // alpha_and stores an 'and' operation of all the alpha[] values. The final
    // value is not 0xff if any of the alpha[] is not equal to 0xff.
    uint32_t alpha_and = 0xff;
    int i, j;
    const __m128i all_0xff = _mm_set1_epi32(~0u);
    __m128i all_alphas = all_0xff;
  
    // We must be able to access 3 extra bytes after the last written byte
    // 'src[4 * width - 4]', because we don't know if alpha is the first or the
    // last byte of the quadruplet.
    const int limit = (width - 1) & ~15;
    const __m128i kCstAlpha0 = _mm_set_epi8(-1, -1, -1, -1, -1, -1, -1, -1,
                                            -1, -1, -1, -1, 12, 8, 4, 0);
    const __m128i kCstAlpha1 = _mm_set_epi8(-1, -1, -1, -1, -1, -1, -1, -1,
                                            12, 8, 4, 0, -1, -1, -1, -1);
    const __m128i kCstAlpha2 = _mm_set_epi8(-1, -1, -1, -1, 12, 8, 4, 0,
                                            -1, -1, -1, -1, -1, -1, -1, -1);
    const __m128i kCstAlpha3 = _mm_set_epi8(12, 8, 4, 0, -1, -1, -1, -1,
                                            -1, -1, -1, -1, -1, -1, -1, -1);
    for (j = 0; j < height; ++j) {
      const __m128i* src = (const __m128i*)argb;
      for (i = 0; i < limit; i += 16) {
        // load 64 argb bytes
        const __m128i a0 = _mm_loadu_si128(src + 0);
        const __m128i a1 = _mm_loadu_si128(src + 1);
        const __m128i a2 = _mm_loadu_si128(src + 2);
        const __m128i a3 = _mm_loadu_si128(src + 3);
        const __m128i b0 = _mm_shuffle_epi8(a0, kCstAlpha0);
        const __m128i b1 = _mm_shuffle_epi8(a1, kCstAlpha1);
        const __m128i b2 = _mm_shuffle_epi8(a2, kCstAlpha2);
        const __m128i b3 = _mm_shuffle_epi8(a3, kCstAlpha3);
        const __m128i c0 = _mm_or_si128(b0, b1);
        const __m128i c1 = _mm_or_si128(b2, b3);
        const __m128i d0 = _mm_or_si128(c0, c1);
        // store
        _mm_storeu_si128((__m128i*)&alpha[i], d0);
        // accumulate sixteen alpha 'and' in parallel
        all_alphas = _mm_and_si128(all_alphas, d0);
        src += 4;
      }
      for (; i < width; ++i) {
        const uint32_t alpha_value = argb[4 * i];
        alpha[i] = alpha_value;
        alpha_and &= alpha_value;
      }
      argb += argb_stride;
      alpha += alpha_stride;
    }
    // Combine the sixteen alpha 'and' into an 8-bit mask.
    alpha_and |= 0xff00u;  // pretend the upper bits [8..15] were tested ok.
    alpha_and &= _mm_movemask_epi8(_mm_cmpeq_epi8(all_alphas, all_0xff));
    return (alpha_and == 0xffffu);
  }
  
  //------------------------------------------------------------------------------
  // Entry point
  
  extern void WebPInitAlphaProcessingSSE41(void);
  
  WEBP_TSAN_IGNORE_FUNCTION void WebPInitAlphaProcessingSSE41(void) {
    WebPExtractAlpha = ExtractAlpha_SSE41;
  }
  
  #else  // !WEBP_USE_SSE41
  
  WEBP_DSP_INIT_STUB(WebPInitAlphaProcessingSSE41)
  
  #endif  // WEBP_USE_SSE41
  