/** @file | |
Compiler intrinsic to return the number of leading zeros, ported from LLVM code. | |
Copyright (c) 2008 - 2009, Apple Inc. All rights reserved.<BR> | |
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)); | |
} |