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

[Tyler Retzlaff]

On Tue, Mar 05, 2024 at 07:08:36PM +0100, Mattias Rönnblom wrote:
> 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 at 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.

i'm curious what misuse pattern you anticipate or have seen that may be
less type-safe? just so i can look out for them.

i (perhaps naively) have liked generic functions for their selection of
the "correct" type and for _Generic if no leg/case exists compiler
error (as opposed to e.g. silent truncation).

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

i was thinking about this overnight, it's supposed to be standard C11
and my use on various compilers showed no problem but I can't recall if
i did any evaluation when consuming as a part of a C++ translation unit
so there could be problems.

> 
> Thanks.
> 
> >Acked-by: Tyler Retzlaff <roretzla at 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