File 0111-Rename-macro-and-add-clarifying-comment.patch of Package erlang

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File 0111-Rename-macro-and-add-clarifying-comment.patch of Package erlang

From 282a7cab9989abb7a1b2daca7aec907d53163ff4 Mon Sep 17 00:00:00 2001
From: Richard Carlsson <richardc@klarna.com>
Date: Thu, 27 Apr 2017 14:44:10 +0200
Subject: [PATCH] Rename macro and add clarifying comment

The macro previously named 'LOG2' is in fact computing the LSB (not the MSB)
of its input, and can only be used to compute log2(n) when n is is a power
of 2, that is, when its LSB is also its MSB.
---
 erts/emulator/sys/common/erl_mseg.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/erts/emulator/sys/common/erl_mseg.c b/erts/emulator/sys/common/erl_mseg.c
index d1895f379..1e9907890 100644
--- a/erts/emulator/sys/common/erl_mseg.c
+++ b/erts/emulator/sys/common/erl_mseg.c
@@ -83,12 +83,13 @@ static const int debruijn[32] = {
     31, 27, 13, 23, 21, 19, 16,  7, 26, 12, 18,  6, 11,  5, 10,  9
 };
 
-#define LOG2(X) (debruijn[((Uint32)(((X) & -(X)) * 0x077CB531U)) >> 27])
+#define LSB(X) (debruijn[((Uint32)(((X) & -(X)) * 0x077CB531U)) >> 27])
 
 #define CACHE_AREAS      (32 - MSEG_ALIGN_BITS)
 
 /* FIXME: segment sizes > 2 GB result in bogus negative indices */
-#define SIZE_TO_CACHE_AREA_IDX(S)   (LOG2((S)) - MSEG_ALIGN_BITS)
+/* NOTE: using LSB instead of proper log2 only works if S is a power of 2 */
+#define SIZE_TO_CACHE_AREA_IDX(S)   (LSB((S)) - MSEG_ALIGN_BITS)
 #define MAX_CACHE_SIZE   (30)
 
 #define MSEG_FLG_IS_2POW(X)    ((X) & ERTS_MSEG_FLG_2POW)
-- 
2.12.2

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File 0111-Rename-macro-and-add-clarifying-comment.patch of Package erlang

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