Re: [Mesa-dev] [PATCH] mesa: fix MSVC bitshift overflow warnings

[Roland Scheidegger]

Am 30.03.2018 um 17:09 schrieb Brian Paul:
> In the BITFIELD_MASK() macro, if b==32 the expression evaluates to
> ~0u, but the compiler still sees the expression (1 << 32) in the
> unused part and issues a warning about integer bitshift overflow.
> 
> Fix that by using (b) % 32 to ensure the max shift is 31 bits.
> 
> This issue has been present for a while, but shows up much more
> often because of the recent VBO changes.
> ---
>  src/mesa/main/mtypes.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/src/mesa/main/mtypes.h b/src/mesa/main/mtypes.h
> index 801bd17..b7a7b34 100644
> --- a/src/mesa/main/mtypes.h
> +++ b/src/mesa/main/mtypes.h
> @@ -59,7 +59,7 @@ extern "C" {
>  #define BITFIELD_BIT(b)  ((GLbitfield)1 << (b))
>  /** Set all bits up to excluding bit b */
>  #define BITFIELD_MASK(b)  \
> -   ((b) == 32 ? (~(GLbitfield)0) : BITFIELD_BIT(b) - 1)
> +   ((b) == 32 ? (~(GLbitfield)0) : BITFIELD_BIT((b) % 32) - 1)
>  /** Set count bits starting from bit b  */
>  #define BITFIELD_RANGE(b, count) \
> (BITFIELD_MASK((b) + (count)) & ~BITFIELD_MASK(b))
> 

Looks reasonable to me.
Reviewed-by: Roland Scheidegger 
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Re: [Mesa-dev] [PATCH] mesa: fix MSVC bitshift overflow warnings

[Mathias Fröhlich]

On Friday, 30 March 2018 17:09:40 CEST Brian Paul wrote:
> In the BITFIELD_MASK() macro, if b==32 the expression evaluates to
> ~0u, but the compiler still sees the expression (1 << 32) in the
> unused part and issues a warning about integer bitshift overflow.
> 
> Fix that by using (b) % 32 to ensure the max shift is 31 bits.
> 
> This issue has been present for a while, but shows up much more
> often because of the recent VBO changes.
> ---
>  src/mesa/main/mtypes.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/src/mesa/main/mtypes.h b/src/mesa/main/mtypes.h
> index 801bd17..b7a7b34 100644
> --- a/src/mesa/main/mtypes.h
> +++ b/src/mesa/main/mtypes.h
> @@ -59,7 +59,7 @@ extern "C" {
>  #define BITFIELD_BIT(b)  ((GLbitfield)1 << (b))
>  /** Set all bits up to excluding bit b */
>  #define BITFIELD_MASK(b)  \
> -   ((b) == 32 ? (~(GLbitfield)0) : BITFIELD_BIT(b) - 1)
> +   ((b) == 32 ? (~(GLbitfield)0) : BITFIELD_BIT((b) % 32) - 1)
>  /** Set count bits starting from bit b  */
>  #define BITFIELD_RANGE(b, count) \
> (BITFIELD_MASK((b) + (count)) & ~BITFIELD_MASK(b))
> 

Definitely:

Reviewed-by: Mathias Fröhlich 

best
Mathias


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[Mesa-dev] [PATCH] mesa: fix MSVC bitshift overflow warnings

[Brian Paul]

In the BITFIELD_MASK() macro, if b==32 the expression evaluates to
~0u, but the compiler still sees the expression (1 << 32) in the
unused part and issues a warning about integer bitshift overflow.

Fix that by using (b) % 32 to ensure the max shift is 31 bits.

This issue has been present for a while, but shows up much more
often because of the recent VBO changes.
---
 src/mesa/main/mtypes.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/mesa/main/mtypes.h b/src/mesa/main/mtypes.h
index 801bd17..b7a7b34 100644
--- a/src/mesa/main/mtypes.h
+++ b/src/mesa/main/mtypes.h
@@ -59,7 +59,7 @@ extern "C" {
 #define BITFIELD_BIT(b)  ((GLbitfield)1 << (b))
 /** Set all bits up to excluding bit b */
 #define BITFIELD_MASK(b)  \
-   ((b) == 32 ? (~(GLbitfield)0) : BITFIELD_BIT(b) - 1)
+   ((b) == 32 ? (~(GLbitfield)0) : BITFIELD_BIT((b) % 32) - 1)
 /** Set count bits starting from bit b  */
 #define BITFIELD_RANGE(b, count) \
(BITFIELD_MASK((b) + (count)) & ~BITFIELD_MASK(b))
-- 
2.7.4

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