1 files changed, 29 insertions, 0 deletions
diff --git a/lib/compiler-rt/builtins/popcountsi2.c b/lib/compiler-rt/builtins/popcountsi2.c
new file mode 100644
index 0000000..4d346c4
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+++ b/lib/compiler-rt/builtins/popcountsi2.c
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+//===-- popcountsi2.c - Implement __popcountsi2 ---------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements __popcountsi2 for the compiler_rt library.
+//
+//===----------------------------------------------------------------------===//
+
+#include "int_lib.h"
+
+// Returns: count of 1 bits
+
+COMPILER_RT_ABI 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)
+}