52 lines
1.4 KiB
C
52 lines
1.4 KiB
C
//===-- clzsi2.c - Implement __clzsi2 -------------------------------------===//
|
|
//
|
|
// The LLVM Compiler Infrastructure
|
|
//
|
|
// This file is distributed under the University of Illinois Open Source
|
|
// License. See LICENSE.TXT for details.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
//
|
|
// This file implements __clzsi2 for the compiler_rt library.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
#include "int_lib.h"
|
|
|
|
// Returns: the number of leading 0-bits
|
|
|
|
// Precondition: a != 0
|
|
|
|
si_int
|
|
__clzsi2(si_int a)
|
|
{
|
|
su_int x = (su_int)a;
|
|
si_int t = ((x & 0xFFFF0000) == 0) << 4; // if (x is small) t = 16 else 0
|
|
x >>= 16 - t; // x = [0 - 0xFFFF]
|
|
su_int 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));
|
|
}
|