diff options
Diffstat (limited to 'lib/builtins/clzsi2.c')
-rw-r--r-- | lib/builtins/clzsi2.c | 89 |
1 files changed, 42 insertions, 47 deletions
diff --git a/lib/builtins/clzsi2.c b/lib/builtins/clzsi2.c index 25b8ed2c4..3f9f27f41 100644 --- a/lib/builtins/clzsi2.c +++ b/lib/builtins/clzsi2.c @@ -1,53 +1,48 @@ -/* ===-- clzsi2.c - Implement __clzsi2 -------------------------------------=== - * - * The LLVM Compiler Infrastructure - * - * This file is dual licensed under the MIT and the University of Illinois Open - * Source Licenses. See LICENSE.TXT for details. - * - * ===----------------------------------------------------------------------=== - * - * This file implements __clzsi2 for the compiler_rt library. - * - * ===----------------------------------------------------------------------=== - */ +//===-- clzsi2.c - Implement __clzsi2 -------------------------------------===// +// +// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. +// See https://llvm.org/LICENSE.txt for license information. +// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception +// +//===----------------------------------------------------------------------===// +// +// This file implements __clzsi2 for the compiler_rt library. +// +//===----------------------------------------------------------------------===// #include "int_lib.h" -/* Returns: the number of leading 0-bits */ +// Returns: the number of leading 0-bits -/* Precondition: a != 0 */ +// Precondition: a != 0 -COMPILER_RT_ABI 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)); +COMPILER_RT_ABI 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)); } |