From b80479ec273dfa3a209e120dc61d9bc9c4f57612 Mon Sep 17 00:00:00 2001
From: David Garcia Quintas <dgq@google.com>
Date: Wed, 15 Jul 2015 17:46:05 -0700
Subject: [PATCH] Added population count function

---
 include/grpc/support/useful.h   | 9 +++++++++
 test/core/support/useful_test.c | 3 +++
 2 files changed, 12 insertions(+)

diff --git a/include/grpc/support/useful.h b/include/grpc/support/useful.h
index d3d8ad6437f..bbd9ea36ae2 100644
--- a/include/grpc/support/useful.h
+++ b/include/grpc/support/useful.h
@@ -34,6 +34,8 @@
 #ifndef GRPC_SUPPORT_USEFUL_H
 #define GRPC_SUPPORT_USEFUL_H
 
+#include <grpc/support/port_platform.h>
+
 /* useful macros that don't belong anywhere else */
 
 #define GPR_MIN(a, b) ((a) < (b) ? (a) : (b))
@@ -61,4 +63,11 @@
 /** Get the \a n-th bit of \a i */
 #define GPR_BITGET(i, n) (((i) & (1u << n)) != 0)
 
+/** Returns number of bits set in bitset \a i */
+int gpr_bitcount(gpr_uint32 i) {
+  i = i - ((i >> 1) & 0x55555555);
+  i = (i & 0x33333333) + ((i >> 2) & 0x33333333);
+  return (((i + (i >> 4)) & 0xF0F0F0F) * 0x1010101) >> 24;
+}
+
 #endif  /* GRPC_SUPPORT_USEFUL_H */
diff --git a/test/core/support/useful_test.c b/test/core/support/useful_test.c
index 5827f0a6276..7129dce632d 100644
--- a/test/core/support/useful_test.c
+++ b/test/core/support/useful_test.c
@@ -57,9 +57,12 @@ int main(int argc, char **argv) {
   GPR_ASSERT(GPR_ARRAY_SIZE(five) == 5);
 
   GPR_ASSERT(GPR_BITSET(&bitset, 3) == 8);
+  GPR_ASSERT(gpr_bitcount(bitset) == 1);
   GPR_ASSERT(GPR_BITGET(bitset, 3) == 1);
   GPR_ASSERT(GPR_BITSET(&bitset, 1) == 10);
+  GPR_ASSERT(gpr_bitcount(bitset) == 2);
   GPR_ASSERT(GPR_BITCLEAR(&bitset, 3) == 2);
+  GPR_ASSERT(gpr_bitcount(bitset) == 1);
   GPR_ASSERT(GPR_BITGET(bitset, 3) == 0);
 
   return 0;