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Note Non-Interoperable Macros and Types #129

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Note Unstable Macros and Types
lenary Oct 15, 2025
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Address Feedback
lenary Oct 17, 2025
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45 changes: 45 additions & 0 deletions src/c-api.adoc
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Expand Up @@ -170,6 +170,51 @@ For example:
|`+__riscv_compressed+` |1 |`C` extension is available. | `+__riscv_c+`
|===

== Non-Interoperable Types and Definitions

There are several implementation-defined C/C++ types and constants that are
usually implemented in RISC-V implementations. The types and constants in this
section should not be relied upon by public interfaces in your code. Their
definitions may be changed by new compiler versions, compiler options, or on a
per-processor basis.

[id=non_interoperable_constants]
.Non-Interoperable C/C++ Constants
[cols="30,~"]
|===
|*Name* |*Description*
|`+std::hardware_constructive_interference_size+` |The maximum recommended size of contiguous memory occupied by two objects accessed with temporal locality by concurrent threads.
|`+std::hardware_destructive_interference_size+` |The minimum recommended offset between two concurrently-accessed objects to avoid additional performance degradation due to contention introduced by the implementation.
|`+INT_FASTN_WIDTH+` |Bit width of an object of type `+int_fastN_t+`
|`+INT_FASTN_MIN+` |Minimum value of an object of type `+int_fastN_t+`
|`+INT_FASTN_MAX+` |Maximum value of an object of type `+int_fastN_t+`
|`+INT_LEASTN_WIDTH+` |Bit width of an object of type `+int_leastN_t+`
|`+INT_LEASTN_MIN+` |Minimum value of an object of type `+int_leastN_t+`
|`+INT_LEASTN_MAX+` |Maximum value of an object of type `+int_leastN_t+`
|`+UINT_FASTN_WIDTH+` |Bit width of an object of type `+uint_fastN_t+`
|`+UINT_FASTN_MAX+` |Maximum value of an object of type `+uint_fastN_t+`
|`+UINT_LEASTN_WIDTH+` |Bit width of an object of type `+uint_leastN_t+`
|`+UINT_LEASTN_MAX+` |Maximum value of an object of type `+uint_leastN_t+`
|===

=== Non-Interoperable Types

Most C type sizes and alignments are defined by the ABI. The following types
should not be relied upon by public interfaces in your code. Their sizes and
alignments are not fixed.

.Non-Interoperable Types
[cols="30,~"]
|===
|*Type* |*Description*
|`+int_fastN_t+` |Fastest signed integer types with widths of at least `+N+` bits.
|`+int_leastN_t+` |Smallest signed integer types with widths of at least `+N+` bits.
|`+uint_fastN_t+` |Fastest unsigned integer types with widths of at least `+N+` bits.
|`+uint_leastN_t+` |Smallest unsigned integer types with widths of at least `+N+` bits.
|===

The corresponding constants are also unstable (see <<non_interoperable_constants, Non-Interoperable Constants>>).

== Function Attributes

=== `+__attribute__((naked))+`
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