diff options
Diffstat (limited to 'contrib/compiler-rt/lib/ctzsi2.c')
-rw-r--r-- | contrib/compiler-rt/lib/ctzsi2.c | 57 |
1 files changed, 57 insertions, 0 deletions
diff --git a/contrib/compiler-rt/lib/ctzsi2.c b/contrib/compiler-rt/lib/ctzsi2.c new file mode 100644 index 0000000..30d34c8 --- /dev/null +++ b/contrib/compiler-rt/lib/ctzsi2.c @@ -0,0 +1,57 @@ +/* ===-- ctzsi2.c - Implement __ctzsi2 -------------------------------------=== + * + * The LLVM Compiler Infrastructure + * + * This file is distributed under the University of Illinois Open Source + * License. See LICENSE.TXT for details. + * + * ===----------------------------------------------------------------------=== + * + * This file implements __ctzsi2 for the compiler_rt library. + * + * ===----------------------------------------------------------------------=== + */ + +#include "int_lib.h" + +/* Returns: the number of trailing 0-bits */ + +/* Precondition: a != 0 */ + +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)); +} |