/*
  * S3 Texture Compression (S3TC) decoding functions
  * Copyright (c) 2007 by Ivo van Poorten
  *

  * see also: http://wiki.multimedia.cx/index.php?title=S3TC
  *

  * This file is part of FFmpeg.
  *
  * FFmpeg is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
  * License as published by the Free Software Foundation; either
  * version 2.1 of the License, or (at your option) any later version.
  *
  * FFmpeg is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Lesser General Public License for more details.
  *
  * You should have received a copy of the GNU Lesser General Public
  * License along with FFmpeg; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 

 #include "libavutil/intreadwrite.h"

 #include "avcodec.h"
 #include "s3tc.h"
 
 static inline void dxt1_decode_pixels(const uint8_t *s, uint32_t *d,
                                       unsigned int qstride, unsigned int flag,
                                       uint64_t alpha) {
     unsigned int x, y, c0, c1, a = (!flag * 255) << 24;
     unsigned int rb0, rb1, rb2, rb3, g0, g1, g2, g3;
     uint32_t colors[4], pixels;
 

     c0 = AV_RL16(s);
     c1 = AV_RL16(s+2);

 
     rb0  = (c0<<3 | c0<<8) & 0xf800f8;
     rb1  = (c1<<3 | c1<<8) & 0xf800f8;
     rb0 +=        (rb0>>5) & 0x070007;
     rb1 +=        (rb1>>5) & 0x070007;
     g0   =        (c0 <<5) & 0x00fc00;
     g1   =        (c1 <<5) & 0x00fc00;
     g0  +=        (g0 >>6) & 0x000300;
     g1  +=        (g1 >>6) & 0x000300;
 
     colors[0] = rb0 + g0 + a;
     colors[1] = rb1 + g1 + a;
 
     if (c0 > c1 || flag) {
         rb2 = (((2*rb0+rb1) * 21) >> 6) & 0xff00ff;
         rb3 = (((2*rb1+rb0) * 21) >> 6) & 0xff00ff;
         g2  = (((2*g0 +g1 ) * 21) >> 6) & 0x00ff00;
         g3  = (((2*g1 +g0 ) * 21) >> 6) & 0x00ff00;
         colors[3] = rb3 + g3 + a;
     } else {
         rb2 = ((rb0+rb1) >> 1) & 0xff00ff;
         g2  = ((g0 +g1 ) >> 1) & 0x00ff00;
         colors[3] = 0;
     }
 
     colors[2] = rb2 + g2 + a;
 

     pixels = AV_RL32(s+4);

     for (y=0; y<4; y++) {
         for (x=0; x<4; x++) {
             a        = (alpha & 0x0f) << 28;
             a       += a >> 4;
             d[x]     = a + colors[pixels&3];
             pixels >>= 2;
             alpha  >>= 4;
         }
         d += qstride;
     }
 }
 
 void ff_decode_dxt1(const uint8_t *s, uint8_t *dst,
                     const unsigned int w, const unsigned int h,
                     const unsigned int stride) {
     unsigned int bx, by, qstride = stride/4;
     uint32_t *d = (uint32_t *) dst;
 
     for (by=0; by < h/4; by++, d += stride-w)
         for (bx=0; bx < w/4; bx++, s+=8, d+=4)
             dxt1_decode_pixels(s, d, qstride, 0, 0LL);
 }
 
 void ff_decode_dxt3(const uint8_t *s, uint8_t *dst,
                     const unsigned int w, const unsigned int h,
                     const unsigned int stride) {
     unsigned int bx, by, qstride = stride/4;
     uint32_t *d = (uint32_t *) dst;
 
     for (by=0; by < h/4; by++, d += stride-w)
         for (bx=0; bx < w/4; bx++, s+=16, d+=4)
             dxt1_decode_pixels(s+8, d, qstride, 1, AV_RL64(s));
 }