Add low level support for 12 bit 420, 422 and 444 YUV video frame conversion.

source/row_common.cc

 /*
  *  Copyright 2011 The LibYuv Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE 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.
  */
 
@@ skipping 2315 matching lines @@
 
     dst_argb[0] = Clamp((int32)(db));
     dst_argb[1] = Clamp((int32)(dg));
     dst_argb[2] = Clamp((int32)(dr));
     dst_argb[3] = Clamp((int32)(da));
     src_argb += 4;
     dst_argb += 4;
   }
 }
 
+// Samples assumed to be unsigned in low 9, 10 or 12 bits.  Scale factor
+// adjust the source integer range to the half float range desired.
+
+// This magic constant is 2^-112. Multiplying by this
+// is the same as subtracting 112 from the exponent, which
+// is the difference in exponent bias between 32-bit and
+// 16-bit floats. Once we've done this subtraction, we can
+// simply extract the low bits of the exponent and the high
+// bits of the mantissa from our float and we're done.
+
+void HalfFloatRow_C(const uint16* src, uint16* dst, float scale, int width) {
+  int i;
+  float mult = 1.9259299444e-34f * scale;
+  for (i = 0; i < width; ++i) {
+    float value = src[i] * mult;
+    dst[i] = (uint16)((*(uint32_t*)&value) >> 13);
+  }
+}
+
 void ARGBLumaColorTableRow_C(const uint8* src_argb, uint8* dst_argb, int width,
                              const uint8* luma, uint32 lumacoeff) {
   uint32 bc = lumacoeff & 0xff;
   uint32 gc = (lumacoeff >> 8) & 0xff;
   uint32 rc = (lumacoeff >> 16) & 0xff;
 
   int i;
   for (i = 0; i < width - 1; i += 2) {
     // Luminance in rows, color values in columns.
     const uint8* luma0 = ((src_argb[0] * bc + src_argb[1] * gc +
@@ skipping 273 matching lines @@
     dst_rgb565 += twidth * 2;
     width -= twidth;
   }
 }
 #endif
 
 #ifdef __cplusplus
 }  // extern "C"
 }  // namespace libyuv
 #endif