vendor/compiler-rt/compiler-rt-r224034

1 files changed, 57 insertions, 0 deletions

diff --git a/lib/builtins/ctzsi2.c b/lib/builtins/ctzsi2.c
new file mode 100644
index 000000000000..c69486ea445f
--- /dev/null
+++ b/lib/builtins/ctzsi2.c
@@ -0,0 +1,57 @@
+/* ===-- 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.
+ *
+ * ===----------------------------------------------------------------------===
+ */
+
+#include "int_lib.h"
+
+/* Returns: the number of trailing 0-bits */
+
+/* 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) */
+
+/*  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));
+}