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add static context object which has no capabilities #553

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merged 2 commits into from
Nov 6, 2018
Merged

add static context object which has no capabilities #553

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ed7c084
add static context object which has no capabilities
apoelstra Aug 15, 2018
40fde61
prevent attempts to modify `secp256k1_context_no_precomp`
apoelstra Sep 20, 2018
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7 changes: 7 additions & 0 deletions include/secp256k1.h
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Original file line number Diff line number Diff line change
Expand Up @@ -179,6 +179,13 @@ typedef int (*secp256k1_nonce_function)(
#define SECP256K1_TAG_PUBKEY_HYBRID_EVEN 0x06
#define SECP256K1_TAG_PUBKEY_HYBRID_ODD 0x07

/** A simple secp256k1 context object with no precomputed tables. These are useful for
* type serialization/parsing functions which require a context object to maintain
* API consistency, but currently do not require expensive precomputations or dynamic
* allocations.
*/
SECP256K1_API extern const secp256k1_context *secp256k1_context_no_precomp;

/** Create a secp256k1 context object.
*
* Returns: a newly created context object.
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12 changes: 12 additions & 0 deletions src/secp256k1.c
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Expand Up @@ -56,6 +56,14 @@ struct secp256k1_context_struct {
secp256k1_callback error_callback;
};

static const secp256k1_context secp256k1_context_no_precomp_ = {
{ 0 },
{ 0 },
{ default_illegal_callback_fn, 0 },
{ default_error_callback_fn, 0 }
};
const secp256k1_context *secp256k1_context_no_precomp = &secp256k1_context_no_precomp_;

secp256k1_context* secp256k1_context_create(unsigned int flags) {
secp256k1_context* ret = (secp256k1_context*)checked_malloc(&default_error_callback, sizeof(secp256k1_context));
ret->illegal_callback = default_illegal_callback;
Expand Down Expand Up @@ -91,6 +99,7 @@ secp256k1_context* secp256k1_context_clone(const secp256k1_context* ctx) {
}

void secp256k1_context_destroy(secp256k1_context* ctx) {
CHECK(ctx != secp256k1_context_no_precomp);
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Are these necessary? A non-const ctx pointer is used, which can't be secp256k1_context_no_precomp (as that one is const).

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Oh, good point. I guess they're not necessary. I can remove them if you want, though I don't mind having them there.

if (ctx != NULL) {
secp256k1_ecmult_context_clear(&ctx->ecmult_ctx);
secp256k1_ecmult_gen_context_clear(&ctx->ecmult_gen_ctx);
Expand All @@ -100,6 +109,7 @@ void secp256k1_context_destroy(secp256k1_context* ctx) {
}

void secp256k1_context_set_illegal_callback(secp256k1_context* ctx, void (*fun)(const char* message, void* data), const void* data) {
CHECK(ctx != secp256k1_context_no_precomp);
if (fun == NULL) {
fun = default_illegal_callback_fn;
}
Expand All @@ -108,6 +118,7 @@ void secp256k1_context_set_illegal_callback(secp256k1_context* ctx, void (*fun)(
}

void secp256k1_context_set_error_callback(secp256k1_context* ctx, void (*fun)(const char* message, void* data), const void* data) {
CHECK(ctx != secp256k1_context_no_precomp);
if (fun == NULL) {
fun = default_error_callback_fn;
}
Expand Down Expand Up @@ -559,6 +570,7 @@ int secp256k1_ec_pubkey_tweak_mul(const secp256k1_context* ctx, secp256k1_pubkey

int secp256k1_context_randomize(secp256k1_context* ctx, const unsigned char *seed32) {
VERIFY_CHECK(ctx != NULL);
CHECK(ctx != secp256k1_context_no_precomp);
ARG_CHECK(secp256k1_ecmult_gen_context_is_built(&ctx->ecmult_gen_ctx));
secp256k1_ecmult_gen_blind(&ctx->ecmult_gen_ctx, seed32);
return 1;
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1 change: 1 addition & 0 deletions src/tests.c
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Expand Up @@ -3599,6 +3599,7 @@ void run_ec_pubkey_parse_test(void) {
ecount = 0;
VG_UNDEF(&pubkey, sizeof(pubkey));
CHECK(secp256k1_ec_pubkey_parse(ctx, &pubkey, pubkeyc, 65) == 1);
CHECK(secp256k1_ec_pubkey_parse(secp256k1_context_no_precomp, &pubkey, pubkeyc, 65) == 1);
VG_CHECK(&pubkey, sizeof(pubkey));
CHECK(ecount == 0);
VG_UNDEF(&ge, sizeof(ge));
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