[PATCH xf86-video-ati] Replace loop with clz to calculate log base 2 on non-x86 platforms in radeon.h

[Jochen Rollwagen <joro-2013-zqRNUXuvxA0b1SvskN2V4Q@public.gmane.org>]

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This commit replaces the loop for calculating log base 2 for 
non-x86-platforms in radeon.h with a clz (count leading zeroes)-based 
version to simplify the code and, well, eliminate the loop.
Note: There’s no check for val=0 case, since x86-bsr is undefined for 
that case too, that should be okay.
---
  src/radeon.h |    7 +++----
  1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/src/radeon.h b/src/radeon.h
index cbc7866..b1a1ce0 100644
--- a/src/radeon.h
+++ b/src/radeon.h
@@ -933,17 +933,16 @@ enum {
  static __inline__ int
  RADEONLog2(int val)
  {
-    int bits;
  #if (defined __i386__ || defined __x86_64__) && (defined __GNUC__)
+    int bits;
+
      __asm volatile("bsrl    %1, %0"
          : "=r" (bits)
          : "c" (val)
      );
      return bits;
  #else
-    for (bits = 0; val != 0; val >>= 1, ++bits)
-        ;
-    return bits - 1;
+    return (31 - __builtin_clz(val));
  #endif
  }

-- 
1.7.9.5


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>From d39f7a0d42fcc423030cd73bff8afe6d39d13e80 Mon Sep 17 00:00:00 2001
From: Jochen Rollwagen <joro-2013-zqRNUXuvxA0b1SvskN2V4Q@public.gmane.org>
Date: Mon, 28 Nov 2016 19:02:13 +0100
Subject: [PATCH] Replace loop with clz to calculate log base 2 on non-x86
 platforms in radeon.h
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

This commit replaces the loop for calculating log base 2 for non-x86-platforms in radeon.h with a clz (count leading zeroes)-based version to simplify the code and, well, eliminate the loop.
Note: There’s no check for val=0 case, since x86-bsr is undefined for that case too, that should be okay.
---
 src/radeon.h |    7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/src/radeon.h b/src/radeon.h
index cbc7866..b1a1ce0 100644
--- a/src/radeon.h
+++ b/src/radeon.h
@@ -933,17 +933,16 @@ enum {
 static __inline__ int
 RADEONLog2(int val)
 {
-	int bits;
 #if (defined __i386__ || defined __x86_64__) && (defined __GNUC__)
+	int bits;
+	
 	__asm volatile("bsrl	%1, %0"
 		: "=r" (bits)
 		: "c" (val)
 	);
 	return bits;
 #else
-	for (bits = 0; val != 0; val >>= 1, ++bits)
-		;
-	return bits - 1;
+	return (31 - __builtin_clz(val));
 #endif
 }
 
-- 
1.7.9.5


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