From 6b8d1aef89ecb24c08f2f4b19903abc2383ca7eb Mon Sep 17 00:00:00 2001
From: David Garcia Quintas <dgq@google.com>
Date: Wed, 15 Jul 2015 18:04:18 -0700
Subject: [PATCH] rewrote bitcount function as a macro

---
 include/grpc/support/useful.h   | 13 ++++++-------
 test/core/support/useful_test.c |  6 +++---
 2 files changed, 9 insertions(+), 10 deletions(-)

diff --git a/include/grpc/support/useful.h b/include/grpc/support/useful.h
index 38072dfc1ea..5b704471235 100644
--- a/include/grpc/support/useful.h
+++ b/include/grpc/support/useful.h
@@ -34,8 +34,6 @@
 #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))
@@ -63,11 +61,12 @@
 /** Get the \a n-th bit of \a i */
 #define GPR_BITGET(i, n) (((i) & (1u << n)) != 0)
 
+#define HEXDIGIT_BITCOUNT_(x)                                    \
+  ((x) - (((x) >> 1) & 0x77777777) - (((x) >> 2) & 0x33333333) - \
+   (((x) >> 3) & 0x11111111))
+
 /** Returns number of bits set in bitset \a i */
-static int gpr_bitcount(gpr_uint32 i) {
-  i = i - ((i >> 1) & 0x55555555);
-  i = (i & 0x33333333) + ((i >> 2) & 0x33333333);
-  return (((i + (i >> 4)) & 0xF0F0F0F) * 0x1010101) >> 24;
-}
+#define GPR_BITCOUNT(x) \
+  (((HEXDIGIT_BITCOUNT_(x) + (HEXDIGIT_BITCOUNT_(x) >> 4)) & 0x0F0F0F0F) % 255)
 
 #endif  /* GRPC_SUPPORT_USEFUL_H */
diff --git a/test/core/support/useful_test.c b/test/core/support/useful_test.c
index 7129dce632d..34f4ce6870a 100644
--- a/test/core/support/useful_test.c
+++ b/test/core/support/useful_test.c
@@ -57,12 +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_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_BITCOUNT(bitset) == 2);
   GPR_ASSERT(GPR_BITCLEAR(&bitset, 3) == 2);
-  GPR_ASSERT(gpr_bitcount(bitset) == 1);
+  GPR_ASSERT(GPR_BITCOUNT(bitset) == 1);
   GPR_ASSERT(GPR_BITGET(bitset, 3) == 0);
 
   return 0;