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Diffstat (limited to 'compiler-rt/lib/builtins/clzsi2.c')
-rw-r--r-- | compiler-rt/lib/builtins/clzsi2.c | 48 |
1 files changed, 48 insertions, 0 deletions
diff --git a/compiler-rt/lib/builtins/clzsi2.c b/compiler-rt/lib/builtins/clzsi2.c new file mode 100644 index 000000000000..3f9f27f41331 --- /dev/null +++ b/compiler-rt/lib/builtins/clzsi2.c @@ -0,0 +1,48 @@ +//===-- 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 + +// 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)); +} |