[RFC 2/7] eal: add generic bit manipulation macros

[Mattias Rönnblom]

On 2024-03-04 09:16, Heng Wang wrote:
> Hi Mattias,
>    I have a comment about the _Generic. What if the user gives uint8_t * or uint16_t * as the address. One improvement is that we could add a default branch in _Generic to throw a compiler error or assert false.

If the user pass an incompatible pointer, the compiler will generate an 
error.

>    Another question is what if nr >= sizeof(type) ? What if you do, for example, (uint32_t)1 << 35? Maybe we could add an assert in the implementation?
> 

There are already such asserts in the functions the macro delegates to.

That said, DPDK RTE_ASSERT()s are disabled even in debug builds, so I'm 
not sure it's going to help anyone.

> Regards,
> Heng
> 
> -----Original Message-----
> From: Mattias Rönnblom <mattias.ronnblom at ericsson.com>
> Sent: Saturday, March 2, 2024 2:53 PM
> To: dev at dpdk.org
> Cc: hofors at lysator.liu.se; Heng Wang <heng.wang at ericsson.com>; Mattias Rönnblom <mattias.ronnblom at ericsson.com>
> Subject: [RFC 2/7] eal: add generic bit manipulation macros
> 
> Add bit-level test/set/clear/assign macros operating on both 32-bit and 64-bit words by means of C11 generic selection.
> 
> Signed-off-by: Mattias Rönnblom <mattias.ronnblom at ericsson.com>
> ---
>   lib/eal/include/rte_bitops.h | 81 ++++++++++++++++++++++++++++++++++++
>   1 file changed, 81 insertions(+)
> 
> diff --git a/lib/eal/include/rte_bitops.h b/lib/eal/include/rte_bitops.h index 9a368724d5..afd0f11033 100644
> --- a/lib/eal/include/rte_bitops.h
> +++ b/lib/eal/include/rte_bitops.h
> @@ -107,6 +107,87 @@ extern "C" {
>   #define RTE_FIELD_GET64(mask, reg) \
>   		((typeof(mask))(((reg) & (mask)) >> rte_ctz64(mask)))
>   
> +/**
> + * Test bit in word.
> + *
> + * Generic selection macro to test the value of a bit in a 32-bit or
> + * 64-bit word. The type of operation depends on the type of the @c
> + * addr parameter.
> + *
> + * This macro does not give any guarantees in regards to memory
> + * ordering or atomicity.
> + *
> + * @param addr
> + *   A pointer to the word to modify.
> + * @param nr
> + *   The index of the bit.
> + */
> +#define rte_bit_test(addr, nr)				\
> +	_Generic((addr),				\
> +		 uint32_t *: rte_bit_test32,		\
> +		 uint64_t *: rte_bit_test64)(addr, nr)
> +
> +/**
> + * Set bit in word.
> + *
> + * Generic selection macro to set a bit in a 32-bit or 64-bit
> + * word. The type of operation depends on the type of the @c addr
> + * parameter.
> + *
> + * This macro does not give any guarantees in regards to memory
> + * ordering or atomicity.
> + *
> + * @param addr
> + *   A pointer to the word to modify.
> + * @param nr
> + *   The index of the bit.
> + */
> +#define rte_bit_set(addr, nr)				\
> +	_Generic((addr),				\
> +		 uint32_t *: rte_bit_set32,		\
> +		 uint64_t *: rte_bit_set64)(addr, nr)
> +
> +/**
> + * Clear bit in word.
> + *
> + * Generic selection macro to clear a bit in a 32-bit or 64-bit
> + * word. The type of operation depends on the type of the @c addr
> + * parameter.
> + *
> + * This macro does not give any guarantees in regards to memory
> + * ordering or atomicity.
> + *
> + * @param addr
> + *   A pointer to the word to modify.
> + * @param nr
> + *   The index of the bit.
> + */
> +#define rte_bit_clear(addr, nr)			\
> +	_Generic((addr),				\
> +		 uint32_t *: rte_bit_clear32,		\
> +		 uint64_t *: rte_bit_clear64)(addr, nr)
> +
> +/**
> + * Assign a value to a bit in word.
> + *
> + * Generic selection macro to assign a value to a bit in a 32-bit or
> +64-bit
> + * word. The type of operation depends on the type of the @c addr parameter.
> + *
> + * This macro does not give any guarantees in regards to memory
> + * ordering or atomicity.
> + *
> + * @param addr
> + *   A pointer to the word to modify.
> + * @param nr
> + *   The index of the bit.
> + * @param value
> + *   The new value of the bit - true for '1', or false for '0'.
> + */
> +#define rte_bit_assign(addr, nr, value)			\
> +	_Generic((addr),				\
> +		 uint32_t *: rte_bit_assign32,			\
> +		 uint64_t *: rte_bit_assign64)(addr, nr, value)
> +
>   /**
>    * Test if a particular bit in a 32-bit word is set.
>    *
> --
> 2.34.1
>