diff options
Diffstat (limited to 'lib/clzsi2.c')
-rw-r--r-- | lib/clzsi2.c | 53 |
1 files changed, 53 insertions, 0 deletions
diff --git a/lib/clzsi2.c b/lib/clzsi2.c new file mode 100644 index 000000000000..7e14af293701 --- /dev/null +++ b/lib/clzsi2.c @@ -0,0 +1,53 @@ +/* ===-- 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)); +} |