diff --git a/include/secp256k1.h b/include/secp256k1.h index b3b5d0e..77ca1b9 100644 --- a/include/secp256k1.h +++ b/include/secp256k1.h @@ -33,9 +33,10 @@ extern "C" { * verification). * * A constructed context can safely be used from multiple threads - * simultaneously, but API call that take a non-const pointer to a context + * simultaneously, but API calls that take a non-const pointer to a context * need exclusive access to it. In particular this is the case for - * secp256k1_context_destroy and secp256k1_context_randomize. + * secp256k1_context_destroy, secp256k1_context_preallocated_destroy, + * and secp256k1_context_randomize. * * Regarding randomization, either do it once at creation time (in which case * you do not need any locking for the other calls), or use a read-write lock. @@ -163,7 +164,8 @@ typedef int (*secp256k1_nonce_function)( #define SECP256K1_FLAGS_BIT_CONTEXT_SIGN (1 << 9) #define SECP256K1_FLAGS_BIT_COMPRESSION (1 << 8) -/** Flags to pass to secp256k1_context_create. */ +/** Flags to pass to secp256k1_context_create, secp256k1_context_preallocated_size, and + * secp256k1_context_preallocated_create. */ #define SECP256K1_CONTEXT_VERIFY (SECP256K1_FLAGS_TYPE_CONTEXT | SECP256K1_FLAGS_BIT_CONTEXT_VERIFY) #define SECP256K1_CONTEXT_SIGN (SECP256K1_FLAGS_TYPE_CONTEXT | SECP256K1_FLAGS_BIT_CONTEXT_SIGN) #define SECP256K1_CONTEXT_NONE (SECP256K1_FLAGS_TYPE_CONTEXT) @@ -186,7 +188,7 @@ typedef int (*secp256k1_nonce_function)( */ SECP256K1_API extern const secp256k1_context *secp256k1_context_no_precomp; -/** Create a secp256k1 context object. +/** Create a secp256k1 context object (in dynamically allocated memory). * * This function uses malloc to allocate memory. It is guaranteed that malloc is * called at most once for every call of this function. @@ -200,7 +202,7 @@ SECP256K1_API secp256k1_context* secp256k1_context_create( unsigned int flags ) SECP256K1_WARN_UNUSED_RESULT; -/** Copies a secp256k1 context object. +/** Copy a secp256k1 context object (into dynamically allocated memory). * * This function uses malloc to allocate memory. It is guaranteed that malloc is * called at most once for every call of this function. @@ -212,14 +214,97 @@ SECP256K1_API secp256k1_context* secp256k1_context_clone( const secp256k1_context* ctx ) SECP256K1_ARG_NONNULL(1) SECP256K1_WARN_UNUSED_RESULT; -/** Destroy a secp256k1 context object. +/** Destroy a secp256k1 context object (created in dynamically allocated memory). * * The context pointer may not be used afterwards. - * Args: ctx: an existing context to destroy (cannot be NULL) + * + * The context to destroy must have been created using secp256k1_context_create + * or secp256k1_context_clone. If the context has instead been created using + * secp256k1_context_preallocated_create or secp256k1_context_preallocated_clone, the + * behaviour is undefined. In that case, secp256k1_context_preallocated_destroy must + * be used instead. + * + * Args: ctx: an existing context to destroy, constructed using + * secp256k1_context_create or secp256k1_context_clone */ SECP256K1_API void secp256k1_context_destroy( secp256k1_context* ctx ); +/** Determine the memory size of a secp256k1 context object to be created in + * caller-provided memory. + * + * The purpose of this function is to determine how much memory must be provided + * to secp256k1_context_preallocated_create. + * + * Returns: the required size of the caller-provided memory block + * In: flags: which parts of the context to initialize. + */ + +SECP256K1_API size_t secp256k1_context_preallocated_size( + unsigned int flags +) SECP256K1_WARN_UNUSED_RESULT; + +/** Create a secp256k1 context object in caller-provided memory. + * + * Returns: a newly created context object. + * In: prealloc: a pointer to a rewritable contiguous block of memory of + * size at least secp256k1_context_preallocated_size(flags) + * bytes, suitably aligned to hold an object of any type + * (cannot be NULL) + * flags: which parts of the context to initialize. + * + * See also secp256k1_context_randomize. + */ +SECP256K1_API secp256k1_context* secp256k1_context_preallocated_create( + void* prealloc, + unsigned int flags +) SECP256K1_ARG_NONNULL(1) SECP256K1_WARN_UNUSED_RESULT; + +/** Determine the memory size of a secp256k1 context object to be copied into + * caller-provided memory. + * + * The purpose of this function is to determine how much memory must be provided + * to secp256k1_context_preallocated_clone when copying the context ctx. + * + * Returns: the required size of the caller-provided memory block. + * In: ctx: an existing context to copy (cannot be NULL) + */ +SECP256K1_API size_t secp256k1_context_preallocated_clone_size( + const secp256k1_context* ctx +) SECP256K1_ARG_NONNULL(1) SECP256K1_WARN_UNUSED_RESULT; + +/** Copy a secp256k1 context object into caller-provided memory. + * + * Returns: a newly created context object. + * Args: ctx: an existing context to copy (cannot be NULL) + * In: prealloc: a pointer to a rewritable contiguous block of memory of + * size at least secp256k1_context_preallocated_size(flags) + * bytes, suitably aligned to hold an object of any type + * (cannot be NULL) + */ +SECP256K1_API secp256k1_context* secp256k1_context_preallocated_clone( + const secp256k1_context* ctx, + void* prealloc +) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_WARN_UNUSED_RESULT; + +/** Destroy a secp256k1 context object that has been created in + * caller-provided memory. + * + * The context pointer may not be used afterwards. + * + * The context to destroy must have been created using + * secp256k1_context_preallocated_create or secp256k1_context_preallocated_clone. + * If the context has instead been created using secp256k1_context_create or + * secp256k1_context_clone, the behaviour is undefined. In that case, + * secp256k1_context_destroy must be used instead. + * + * Args: ctx: an existing context to destroy, constructed using + * secp256k1_context_preallocated_create or + * secp256k1_context_preallocated_clone (cannot be NULL) + */ +SECP256K1_API void secp256k1_context_preallocated_destroy( + secp256k1_context* ctx +); /** Set a callback function to be called when an illegal argument is passed to * an API call. It will only trigger for violations that are mentioned @@ -642,7 +727,8 @@ SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_pubkey_tweak_mul( * contexts not initialized for signing; then it will have no effect and return 1. * * You should call this after secp256k1_context_create or - * secp256k1_context_clone, and may call this repeatedly afterwards. + * secp256k1_context_clone (and secp256k1_context_preallocated_create or + * secp256k1_context_clone, resp.), and you may call this repeatedly afterwards. */ SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_context_randomize( secp256k1_context* ctx,