Initial import

third_party/compiler_rt/clzsi2.c

@@ -0,0 +1,56 @@
+/* clang-format off */
+/* ===-- clzsi2.c - Implement __clzsi2 -------------------------------------===
+ *
+ *               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 __clzsi2 for the compiler_rt library.
+ *
+ * ===----------------------------------------------------------------------===
+ */
+
+STATIC_YOINK("huge_compiler_rt_license");
+
+#include "third_party/compiler_rt/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));
+}