From: Alok Hota <alok.hota@intel.com>
Date: Tue, 14 Aug 2018 17:36:00 +0000 (-0500)
Subject: swr/rast: Flip BitScanReverse index calculation
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=05e4ff33f5c717275e88844e67d0fc3dd12d9d2b;p=mesa.git

swr/rast: Flip BitScanReverse index calculation

The intrinsic returns the number of leading zeros, not the bit number of
the first nonzero, so just flip it based on the mask size

Reviewed-by: Bruce Cherniak <bruce.cherniak@intel.com>
---

diff --git a/src/gallium/drivers/swr/rasterizer/common/os.h b/src/gallium/drivers/swr/rasterizer/common/os.h
index d685467906b..314d8184374 100644
--- a/src/gallium/drivers/swr/rasterizer/common/os.h
+++ b/src/gallium/drivers/swr/rasterizer/common/os.h
@@ -202,13 +202,13 @@ inline unsigned char _BitScanForward(unsigned int* Index, unsigned int Mask)
 
 inline unsigned char _BitScanReverse(unsigned long* Index, unsigned long Mask)
 {
-    *Index = __builtin_clz(Mask);
+    *Index = 63 - __builtin_clz(Mask);
     return (Mask != 0);
 }
 
 inline unsigned char _BitScanReverse(unsigned int* Index, unsigned int Mask)
 {
-    *Index = __builtin_clz(Mask);
+    *Index = 31 - __builtin_clz(Mask);
     return (Mask != 0);
 }