; ; Copyright (c) 2010 The WebM 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. ;
%include"vpx_ports/x86_abi_support.asm"
; /**************************************************************************** ; * Notes: ; * ; * This implementation makes use of 16 bit fixed point version of two multiply ; * constants: ; * 1. sqrt(2) * cos (pi/8) ; * 2. sqrt(2) * sin (pi/8) ; * Because the first constant is bigger than 1, to maintain the same 16 bit ; * fixed point precision as the second one, we use a trick of ; * x * a = x + x*(a-1) ; * so ; * x * sqrt(2) * cos (pi/8) = x + x * (sqrt(2) *cos(pi/8)-1). ; * ; * For the second constant, because of the 16bit version is 35468, which ; * is bigger than 32768, in signed 16 bit multiply, it becomes a negative ; * number. ; * (x * (unsigned)35468 >> 16) = x * (signed)35468 >> 16 + x ; * ; **************************************************************************/
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