diff options
Diffstat (limited to 'lib/builtins/ctzsi2.c')
-rw-r--r-- | lib/builtins/ctzsi2.c | 96 |
1 files changed, 46 insertions, 50 deletions
diff --git a/lib/builtins/ctzsi2.c b/lib/builtins/ctzsi2.c index c69486ea4..09c6863b7 100644 --- a/lib/builtins/ctzsi2.c +++ b/lib/builtins/ctzsi2.c @@ -1,57 +1,53 @@ -/* ===-- ctzsi2.c - Implement __ctzsi2 -------------------------------------=== - * - * 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 __ctzsi2 for the compiler_rt library. - * - * ===----------------------------------------------------------------------=== - */ +//===-- ctzsi2.c - Implement __ctzsi2 -------------------------------------===// +// +// 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 __ctzsi2 for the compiler_rt library. +// +//===----------------------------------------------------------------------===// #include "int_lib.h" -/* Returns: the number of trailing 0-bits */ +// Returns: the number of trailing 0-bits -/* Precondition: a != 0 */ +// Precondition: a != 0 -COMPILER_RT_ABI si_int -__ctzsi2(si_int a) -{ - su_int x = (su_int)a; - si_int t = ((x & 0x0000FFFF) == 0) << 4; /* if (x has no small bits) t = 16 else 0 */ - x >>= t; /* x = [0 - 0xFFFF] + higher garbage bits */ - su_int r = t; /* r = [0, 16] */ - /* return r + ctz(x) */ - t = ((x & 0x00FF) == 0) << 3; - x >>= t; /* x = [0 - 0xFF] + higher garbage bits */ - r += t; /* r = [0, 8, 16, 24] */ - /* return r + ctz(x) */ - t = ((x & 0x0F) == 0) << 2; - x >>= t; /* x = [0 - 0xF] + higher garbage bits */ - r += t; /* r = [0, 4, 8, 12, 16, 20, 24, 28] */ - /* return r + ctz(x) */ - t = ((x & 0x3) == 0) << 1; - x >>= t; - x &= 3; /* x = [0 - 3] */ - r += t; /* r = [0 - 30] and is even */ - /* return r + ctz(x) */ +COMPILER_RT_ABI si_int __ctzsi2(si_int a) { + su_int x = (su_int)a; + si_int t = ((x & 0x0000FFFF) == 0) + << 4; // if (x has no small bits) t = 16 else 0 + x >>= t; // x = [0 - 0xFFFF] + higher garbage bits + su_int r = t; // r = [0, 16] + // return r + ctz(x) + t = ((x & 0x00FF) == 0) << 3; + x >>= t; // x = [0 - 0xFF] + higher garbage bits + r += t; // r = [0, 8, 16, 24] + // return r + ctz(x) + t = ((x & 0x0F) == 0) << 2; + x >>= t; // x = [0 - 0xF] + higher garbage bits + r += t; // r = [0, 4, 8, 12, 16, 20, 24, 28] + // return r + ctz(x) + t = ((x & 0x3) == 0) << 1; + x >>= t; + x &= 3; // x = [0 - 3] + r += t; // r = [0 - 30] and is even + // return r + ctz(x) -/* The branch-less return statement below is equivalent - * to the following switch statement: - * switch (x) - * { - * case 0: - * return r + 2; - * case 2: - * return r + 1; - * case 1: - * case 3: - * return r; - * } - */ - return r + ((2 - (x >> 1)) & -((x & 1) == 0)); + // The branch-less return statement below is equivalent + // to the following switch statement: + // switch (x) + // { + // case 0: + // return r + 2; + // case 2: + // return r + 1; + // case 1: + // case 3: + // return r; + // } + return r + ((2 - (x >> 1)) & -((x & 1) == 0)); } |