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

["Mattias Rönnblom" <hofors@lysator.liu.se>]

On 2024-03-04 17:42, Tyler Retzlaff wrote:
> On Sat, Mar 02, 2024 at 02:53:23PM +0100, Mattias Rönnblom wrote:
>> 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@ericsson.com>
>> ---
> 
> _Generic is nice here. should we discourage direct use of the inline
> functions in preference of using the macro always? either way lgtm.
> 

That was something I considered, but decided against it for RFC v1. I 
wasn't even sure people would like _Generic.

The big upside of having only the _Generic macros would be a much 
smaller API, but maybe a tiny bit less (type-)safe to use.

Also, _Generic is new for DPDK, so who knows what issues it might cause 
with old compilers.

Thanks.

> Acked-by: Tyler Retzlaff <roretzla@linux.microsoft.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