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

include/libyuv/planar_functions.h

 /*
  *  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 263 matching lines @@
 // the 3, g to the 3, r to the 3 and a to the 3.  The values are summed and
 // result clamped to 0 to 255.
 // A polynomial approximation can be dirived using software such as 'R'.
 
 LIBYUV_API
 int ARGBPolynomial(const uint8* src_argb, int src_stride_argb,
                    uint8* dst_argb, int dst_stride_argb,
                    const float* poly,
                    int width, int height);
 
+// Convert plane of 16 bit shorts to half floats.
+// Source values are multiplied by scale before storing as half float.
+LIBYUV_API
+int HalfFloatPlane(const uint16* src_y, int src_stride_y,
+                   uint16* dst_y, int dst_stride_y,
+                   float scale,
+                   int width, int height);
+
 // Quantize a rectangle of ARGB. Alpha unaffected.
 // scale is a 16 bit fractional fixed point scaler between 0 and 65535.
 // interval_size should be a value between 1 and 255.
 // interval_offset should be a value between 0 and 255.
 LIBYUV_API
 int ARGBQuantize(uint8* dst_argb, int dst_stride_argb,
                  int scale, int interval_size, int interval_offset,
                  int x, int y, int width, int height);
 
 // Copy ARGB to ARGB.
@@ skipping 218 matching lines @@
 int ARGBSobelXY(const uint8* src_argb, int src_stride_argb,
                 uint8* dst_argb, int dst_stride_argb,
                 int width, int height);
 
 #ifdef __cplusplus
 }  // extern "C"
 }  // namespace libyuv
 #endif
 
 #endif  // INCLUDE_LIBYUV_PLANAR_FUNCTIONS_H_