[PATCH v3 06/16] hash: add a function to look up hash algo structs
From: brian m. carlson <hidden>
Date: 2026-02-07 20:05:05
Subsystem:
the rest · Maintainer:
Linus Torvalds
In C, it's easy for us to look up a hash algorithm structure by its offset by simply indexing the hash_algos array. However, in Rust, we sometimes need a pointer to pass to a C function, but we have our own hash algorithm abstraction. To get one from the other, let's provide a simple function that looks up the C structure from the offset and expose it in Rust. Signed-off-by: brian m. carlson <redacted> --- hash.c | 7 +++++++ hash.h | 1 + src/hash.rs | 14 ++++++++++++++ 3 files changed, 22 insertions(+)
diff --git a/hash.c b/hash.c
index 81b4f87027..97fd473607 100644
--- a/hash.c
+++ b/hash.c@@ -241,6 +241,13 @@ const char *empty_tree_oid_hex(const struct git_hash_algo *algop) return oid_to_hex_r(buf, algop->empty_tree); } +const struct git_hash_algo *hash_algo_ptr_by_number(uint32_t algo) +{ + if (algo >= GIT_HASH_NALGOS) + return NULL; + return &hash_algos[algo]; +} + uint32_t hash_algo_by_name(const char *name) { if (!name)
diff --git a/hash.h b/hash.h
index 99c9c2a0a8..709d7585a5 100644
--- a/hash.h
+++ b/hash.h@@ -340,6 +340,7 @@ static inline void git_hash_final_oid(struct object_id *oid, struct git_hash_ctx ctx->algop->final_oid_fn(oid, ctx); } +const struct git_hash_algo *hash_algo_ptr_by_number(uint32_t algo); /* * Return a GIT_HASH_* constant based on the name. Returns GIT_HASH_UNKNOWN if * the name doesn't match a known algorithm.
diff --git a/src/hash.rs b/src/hash.rs
index 0ec0ab0490..70bb8095e8 100644
--- a/src/hash.rs
+++ b/src/hash.rs@@ -12,6 +12,7 @@ use std::error::Error; use std::fmt::{self, Debug, Display}; +use std::os::raw::c_void; pub const GIT_MAX_RAWSZ: usize = 32;
@@ -177,4 +178,17 @@ impl HashAlgorithm { HashAlgorithm::SHA256 => &Self::SHA256_NULL_OID, } } + + /// A pointer to the C `struct git_hash_algo` for interoperability with C. + pub fn hash_algo_ptr(self) -> *const c_void { + unsafe { c::hash_algo_ptr_by_number(self as u32) } + } +} + +pub mod c { + use std::os::raw::c_void; + + extern "C" { + pub fn hash_algo_ptr_by_number(n: u32) -> *const c_void; + } }