mirror of https://github.com/acidanthera/audk.git
97 lines
3.4 KiB
C
97 lines
3.4 KiB
C
/** @file
|
|
Compiler intrinsic to return the number of leading zeros, ported from LLVM code.
|
|
|
|
Copyright (c) 2008-2009, Apple Inc. All rights reserved.
|
|
|
|
All rights reserved. This program and the accompanying materials
|
|
are licensed and made available under the terms and conditions of the BSD License
|
|
which accompanies this distribution. The full text of the license may be found at
|
|
http://opensource.org/licenses/bsd-license.php
|
|
|
|
THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
|
|
WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
|
|
|
|
**/
|
|
/**
|
|
University of Illinois/NCSA
|
|
Open Source License
|
|
|
|
Copyright (c) 2003-2008 University of Illinois at Urbana-Champaign.
|
|
All rights reserved.
|
|
|
|
Developed by:
|
|
|
|
LLVM Team
|
|
|
|
University of Illinois at Urbana-Champaign
|
|
|
|
http://llvm.org
|
|
|
|
Permission is hereby granted, free of charge, to any person obtaining a copy of
|
|
this software and associated documentation files (the "Software"), to deal with
|
|
the Software without restriction, including without limitation the rights to
|
|
use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
|
|
of the Software, and to permit persons to whom the Software is furnished to do
|
|
so, subject to the following conditions:
|
|
|
|
* Redistributions of source code must retain the above copyright notice,
|
|
this list of conditions and the following disclaimers.
|
|
|
|
* Redistributions in binary form must reproduce the above copyright notice,
|
|
this list of conditions and the following disclaimers in the
|
|
documentation and/or other materials provided with the distribution.
|
|
|
|
* Neither the names of the LLVM Team, University of Illinois at
|
|
Urbana-Champaign, nor the names of its contributors may be used to
|
|
endorse or promote products derived from this Software without specific
|
|
prior written permission.
|
|
|
|
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
|
|
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
|
|
FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
|
|
CONTRIBUTORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
|
|
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
|
|
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS WITH THE
|
|
SOFTWARE.
|
|
**/
|
|
|
|
|
|
#include "Llvm_int_lib.h"
|
|
|
|
// Returns: the number of leading 0-bits
|
|
|
|
// Precondition: a != 0
|
|
|
|
INT32
|
|
__clzsi2(INT32 a)
|
|
{
|
|
UINT32 x = (UINT32)a;
|
|
INT32 t = ((x & 0xFFFF0000) == 0) << 4; // if (x is small) t = 16 else 0
|
|
x >>= 16 - t; // x = [0 - 0xFFFF]
|
|
UINT32 r = t; // r = [0, 16]
|
|
// return r + clz(x)
|
|
t = ((x & 0xFF00) == 0) << 3;
|
|
x >>= 8 - t; // x = [0 - 0xFF]
|
|
r += t; // r = [0, 8, 16, 24]
|
|
// return r + clz(x)
|
|
t = ((x & 0xF0) == 0) << 2;
|
|
x >>= 4 - t; // x = [0 - 0xF]
|
|
r += t; // r = [0, 4, 8, 12, 16, 20, 24, 28]
|
|
// return r + clz(x)
|
|
t = ((x & 0xC) == 0) << 1;
|
|
x >>= 2 - t; // x = [0 - 3]
|
|
r += t; // r = [0 - 30] and is even
|
|
// return r + clz(x)
|
|
// switch (x)
|
|
// {
|
|
// case 0:
|
|
// return r + 2;
|
|
// case 1:
|
|
// return r + 1;
|
|
// case 2:
|
|
// case 3:
|
|
// return r;
|
|
// }
|
|
return r + ((2 - x) & -((x & 2) == 0));
|
|
}
|