Initial import

third_party/compiler_rt/popcountsi2.c

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+/* clang-format off */
+/* ===-- popcountsi2.c - Implement __popcountsi2 ---------------------------===
+ *
+ *                     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 __popcountsi2 for the compiler_rt library.
+ *
+ * ===----------------------------------------------------------------------===
+ */
+
+STATIC_YOINK("huge_compiler_rt_license");
+
+#include "third_party/compiler_rt/int_lib.h"
+
+/* Returns: count of 1 bits */
+
+COMPILER_RT_ABI si_int
+__popcountsi2(si_int a)
+{
+    su_int x = (su_int)a;
+    x = x - ((x >> 1) & 0x55555555);
+    /* Every 2 bits holds the sum of every pair of bits */
+    x = ((x >> 2) & 0x33333333) + (x & 0x33333333);
+    /* Every 4 bits holds the sum of every 4-set of bits (3 significant bits) */
+    x = (x + (x >> 4)) & 0x0F0F0F0F;
+    /* Every 8 bits holds the sum of every 8-set of bits (4 significant bits) */
+    x = (x + (x >> 16));
+    /* The lower 16 bits hold two 8 bit sums (5 significant bits).*/
+    /*    Upper 16 bits are garbage */
+    return (x + (x >> 8)) & 0x0000003F;  /* (6 significant bits) */
+}