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scratch: replace frames with "checkpoint" system
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@apoelstra
apoelstra committed May 26, 2019
1 parent 7623cf2 commit 98836b1
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Showing 4 changed files with 98 additions and 80 deletions.
30 changes: 20 additions & 10 deletions src/ecmult_impl.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -653,15 +653,13 @@ static int secp256k1_ecmult_strauss_batch(const secp256k1_callback* error_callba
secp256k1_scalar* scalars;
struct secp256k1_strauss_state state;
size_t i;
const size_t scratch_checkpoint = secp256k1_scratch_checkpoint(error_callback, scratch);

secp256k1_gej_set_infinity(r);
if (inp_g_sc == NULL && n_points == 0) {
return 1;
}

if (!secp256k1_scratch_allocate_frame(error_callback, scratch, secp256k1_strauss_scratch_size(n_points), STRAUSS_SCRATCH_OBJECTS)) {
return 0;
}
points = (secp256k1_gej*)secp256k1_scratch_alloc(error_callback, scratch, n_points * sizeof(secp256k1_gej));
scalars = (secp256k1_scalar*)secp256k1_scratch_alloc(error_callback, scratch, n_points * sizeof(secp256k1_scalar));
state.prej = (secp256k1_gej*)secp256k1_scratch_alloc(error_callback, scratch, n_points * ECMULT_TABLE_SIZE(WINDOW_A) * sizeof(secp256k1_gej));
Expand All @@ -674,16 +672,21 @@ static int secp256k1_ecmult_strauss_batch(const secp256k1_callback* error_callba
#endif
state.ps = (struct secp256k1_strauss_point_state*)secp256k1_scratch_alloc(error_callback, scratch, n_points * sizeof(struct secp256k1_strauss_point_state));

if (points == NULL || scalars == NULL || state.prej == NULL || state.zr == NULL || state.pre_a == NULL) {
secp256k1_scratch_apply_checkpoint(error_callback, scratch, scratch_checkpoint);
return 0;
}

for (i = 0; i < n_points; i++) {
secp256k1_ge point;
if (!cb(&scalars[i], &point, i+cb_offset, cbdata)) {
secp256k1_scratch_deallocate_frame(error_callback, scratch);
secp256k1_scratch_apply_checkpoint(error_callback, scratch, scratch_checkpoint);
return 0;
}
secp256k1_gej_set_ge(&points[i], &point);
}
secp256k1_ecmult_strauss_wnaf(ctx, &state, r, n_points, points, scalars, inp_g_sc);
secp256k1_scratch_deallocate_frame(error_callback, scratch);
secp256k1_scratch_apply_checkpoint(error_callback, scratch, scratch_checkpoint);
return 1;
}

Expand Down Expand Up @@ -986,6 +989,7 @@ static size_t secp256k1_pippenger_scratch_size(size_t n_points, int bucket_windo
}

static int secp256k1_ecmult_pippenger_batch(const secp256k1_callback* error_callback, const secp256k1_ecmult_context *ctx, secp256k1_scratch *scratch, secp256k1_gej *r, const secp256k1_scalar *inp_g_sc, secp256k1_ecmult_multi_callback cb, void *cbdata, size_t n_points, size_t cb_offset) {
const size_t scratch_checkpoint = secp256k1_scratch_checkpoint(error_callback, scratch);
/* Use 2(n+1) with the endomorphism, n+1 without, when calculating batch
* sizes. The reason for +1 is that we add the G scalar to the list of
* other scalars. */
Expand All @@ -1010,15 +1014,21 @@ static int secp256k1_ecmult_pippenger_batch(const secp256k1_callback* error_call
}

bucket_window = secp256k1_pippenger_bucket_window(n_points);
if (!secp256k1_scratch_allocate_frame(error_callback, scratch, secp256k1_pippenger_scratch_size(n_points, bucket_window), PIPPENGER_SCRATCH_OBJECTS)) {
return 0;
}
points = (secp256k1_ge *) secp256k1_scratch_alloc(error_callback, scratch, entries * sizeof(*points));
scalars = (secp256k1_scalar *) secp256k1_scratch_alloc(error_callback, scratch, entries * sizeof(*scalars));
state_space = (struct secp256k1_pippenger_state *) secp256k1_scratch_alloc(error_callback, scratch, sizeof(*state_space));
if (points == NULL || scalars == NULL || state_space == NULL) {
secp256k1_scratch_apply_checkpoint(error_callback, scratch, scratch_checkpoint);
return 0;
}

state_space->ps = (struct secp256k1_pippenger_point_state *) secp256k1_scratch_alloc(error_callback, scratch, entries * sizeof(*state_space->ps));
state_space->wnaf_na = (int *) secp256k1_scratch_alloc(error_callback, scratch, entries*(WNAF_SIZE(bucket_window+1)) * sizeof(int));
buckets = (secp256k1_gej *) secp256k1_scratch_alloc(error_callback, scratch, (1<<bucket_window) * sizeof(*buckets));
if (state_space->ps == NULL || state_space->wnaf_na == NULL || buckets == NULL) {
secp256k1_scratch_apply_checkpoint(error_callback, scratch, scratch_checkpoint);
return 0;
}

if (inp_g_sc != NULL) {
scalars[0] = *inp_g_sc;
Expand All @@ -1032,7 +1042,7 @@ static int secp256k1_ecmult_pippenger_batch(const secp256k1_callback* error_call

while (point_idx < n_points) {
if (!cb(&scalars[idx], &points[idx], point_idx + cb_offset, cbdata)) {
secp256k1_scratch_deallocate_frame(error_callback, scratch);
secp256k1_scratch_apply_checkpoint(error_callback, scratch, scratch_checkpoint);
return 0;
}
idx++;
Expand All @@ -1056,7 +1066,7 @@ static int secp256k1_ecmult_pippenger_batch(const secp256k1_callback* error_call
for(i = 0; i < 1<<bucket_window; i++) {
secp256k1_gej_clear(&buckets[i]);
}
secp256k1_scratch_deallocate_frame(error_callback, scratch);
secp256k1_scratch_apply_checkpoint(error_callback, scratch, scratch_checkpoint);
return 1;
}

Expand Down
22 changes: 12 additions & 10 deletions src/scratch.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -7,29 +7,31 @@
#ifndef _SECP256K1_SCRATCH_
#define _SECP256K1_SCRATCH_

#define SECP256K1_SCRATCH_MAX_FRAMES 5

/* The typedef is used internally; the struct name is used in the public API
* (where it is exposed as a different typedef) */
typedef struct secp256k1_scratch_space_struct {
/** guard against interpreting this object as other types */
unsigned char magic[8];
/** actual allocated data */
void *data;
void *current_frame;
size_t offset[SECP256K1_SCRATCH_MAX_FRAMES];
size_t frame_size[SECP256K1_SCRATCH_MAX_FRAMES];
size_t frame;
/** amount that has been allocated (i.e. `data + offset` is the next
* available pointer) */
size_t alloc_size;
/** maximum size available to allocate */
size_t max_size;
} secp256k1_scratch;

static secp256k1_scratch* secp256k1_scratch_create(const secp256k1_callback* error_callback, size_t max_size);

static void secp256k1_scratch_destroy(const secp256k1_callback* error_callback, secp256k1_scratch* scratch);

/** Attempts to allocate a new stack frame with `n` available bytes. Returns 1 on success, 0 on failure */
static int secp256k1_scratch_allocate_frame(const secp256k1_callback* error_callback, secp256k1_scratch* scratch, size_t n, size_t objects);
/** Returns an opaque object used to "checkpoint" a scratch space. Used
* with `secp256k1_scratch_apply_checkpoint` to undo allocations. */
static size_t secp256k1_scratch_checkpoint(const secp256k1_callback* error_callback, const secp256k1_scratch* scratch);

/** Deallocates a stack frame */
static void secp256k1_scratch_deallocate_frame(const secp256k1_callback* error_callback, secp256k1_scratch* scratch);
/** Applies a check point received from `secp256k1_scratch_checkpoint`,
* undoing all allocations since that point. */
static void secp256k1_scratch_apply_checkpoint(const secp256k1_callback* error_callback, secp256k1_scratch* scratch, size_t checkpoint);

/** Returns the maximum allocation the scratch space will allow */
static size_t secp256k1_scratch_max_allocation(const secp256k1_callback* error_callback, const secp256k1_scratch* scratch, size_t n_objects);
Expand Down
55 changes: 18 additions & 37 deletions src/scratch_impl.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -25,7 +25,7 @@ static secp256k1_scratch* secp256k1_scratch_create(const secp256k1_callback* err

static void secp256k1_scratch_destroy(const secp256k1_callback* error_callback, secp256k1_scratch* scratch) {
if (scratch != NULL) {
VERIFY_CHECK(scratch->frame == 0);
VERIFY_CHECK(scratch->alloc_size == 0); /* all checkpoints should be applied */
if (memcmp(scratch->magic, "scratch", 8) != 0) {
secp256k1_callback_call(error_callback, "invalid scratch space");
return;
Expand All @@ -35,71 +35,52 @@ static void secp256k1_scratch_destroy(const secp256k1_callback* error_callback,
}
}

static size_t secp256k1_scratch_max_allocation(const secp256k1_callback* error_callback, const secp256k1_scratch* scratch, size_t objects) {
size_t i = 0;
size_t allocated = 0;
static size_t secp256k1_scratch_checkpoint(const secp256k1_callback* error_callback, const secp256k1_scratch* scratch) {
if (memcmp(scratch->magic, "scratch", 8) != 0) {
secp256k1_callback_call(error_callback, "invalid scratch space");
return 0;
}
for (i = 0; i < scratch->frame; i++) {
allocated += scratch->frame_size[i];
}
if (scratch->max_size - allocated <= objects * (ALIGNMENT - 1)) {
return 0;
}
return scratch->max_size - allocated - objects * (ALIGNMENT - 1);
return scratch->alloc_size;
}

static int secp256k1_scratch_allocate_frame(const secp256k1_callback* error_callback, secp256k1_scratch* scratch, size_t n, size_t objects) {
VERIFY_CHECK(scratch->frame < SECP256K1_SCRATCH_MAX_FRAMES);

static void secp256k1_scratch_apply_checkpoint(const secp256k1_callback* error_callback, secp256k1_scratch* scratch, size_t checkpoint) {
if (memcmp(scratch->magic, "scratch", 8) != 0) {
secp256k1_callback_call(error_callback, "invalid scratch space");
return 0;
return;
}

if (n <= secp256k1_scratch_max_allocation(error_callback, scratch, objects)) {
n += objects * (ALIGNMENT - 1);
scratch->current_frame = scratch->data;
scratch->data = (void *) ((char *) scratch->data + n);
scratch->frame_size[scratch->frame] = n;
scratch->offset[scratch->frame] = 0;
scratch->frame++;
return 1;
} else {
return 0;
if (checkpoint > scratch->alloc_size) {
secp256k1_callback_call(error_callback, "invalid checkpoint");
return;
}
scratch->alloc_size = checkpoint;
}

static void secp256k1_scratch_deallocate_frame(const secp256k1_callback* error_callback, secp256k1_scratch* scratch) {
static size_t secp256k1_scratch_max_allocation(const secp256k1_callback* error_callback, const secp256k1_scratch* scratch, size_t objects) {
if (memcmp(scratch->magic, "scratch", 8) != 0) {
secp256k1_callback_call(error_callback, "invalid scratch space");
return;
return 0;
}

VERIFY_CHECK(scratch->frame > 0);

scratch->frame--;
scratch->data = (void *) ((char *) scratch->data - scratch->frame_size[scratch->frame]);
if (scratch->max_size - scratch->alloc_size <= objects * (ALIGNMENT - 1)) {
return 0;
}
return scratch->max_size - scratch->alloc_size - objects * (ALIGNMENT - 1);
}

static void *secp256k1_scratch_alloc(const secp256k1_callback* error_callback, secp256k1_scratch* scratch, size_t size) {
void *ret;
size_t frame = scratch->frame - 1;
size = ROUND_TO_ALIGN(size);

if (memcmp(scratch->magic, "scratch", 8) != 0) {
secp256k1_callback_call(error_callback, "invalid scratch space");
return NULL;
}

if (scratch->frame == 0 || size + scratch->offset[frame] > scratch->frame_size[frame]) {
if (size > scratch->max_size - scratch->alloc_size) {
return NULL;
}
ret = (void *) ((char *) scratch->current_frame + scratch->offset[frame]);
ret = (void *) ((char *) scratch->data + scratch->alloc_size);
memset(ret, 0, size);
scratch->offset[frame] += size;
scratch->alloc_size += size;

return ret;
}
Expand Down
71 changes: 48 additions & 23 deletions src/tests.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -333,7 +333,11 @@ void run_context_tests(int use_prealloc) {
}

void run_scratch_tests(void) {
const size_t adj_alloc = ((500 + ALIGNMENT - 1) / ALIGNMENT) * ALIGNMENT;

int32_t ecount = 0;
size_t checkpoint;
size_t checkpoint_2;
secp256k1_context *none = secp256k1_context_create(SECP256K1_CONTEXT_NONE);
secp256k1_scratch_space *scratch;
secp256k1_scratch_space local_scratch;
Expand All @@ -348,43 +352,54 @@ void run_scratch_tests(void) {

/* Test internal API */
CHECK(secp256k1_scratch_max_allocation(&none->error_callback, scratch, 0) == 1000);
CHECK(secp256k1_scratch_max_allocation(&none->error_callback, scratch, 1) < 1000);

/* Allocating 500 bytes with no frame fails */
CHECK(secp256k1_scratch_alloc(&none->error_callback, scratch, 500) == NULL);
CHECK(secp256k1_scratch_max_allocation(&none->error_callback, scratch, 0) == 1000);
CHECK(secp256k1_scratch_max_allocation(&none->error_callback, scratch, 1) == 1000 - (ALIGNMENT - 1));
CHECK(scratch->alloc_size == 0);
CHECK(scratch->alloc_size % ALIGNMENT == 0);

/* ...but pushing a new stack frame does affect the max allocation */
CHECK(secp256k1_scratch_allocate_frame(&none->error_callback, scratch, 500, 1) == 1);
CHECK(secp256k1_scratch_max_allocation(&none->error_callback, scratch, 1) < 500); /* 500 - (ALIGNMENT - 1) */
/* Allocating 500 bytes succeeds */
checkpoint = secp256k1_scratch_checkpoint(&none->error_callback, scratch);
CHECK(secp256k1_scratch_alloc(&none->error_callback, scratch, 500) != NULL);
CHECK(secp256k1_scratch_alloc(&none->error_callback, scratch, 500) == NULL);

CHECK(secp256k1_scratch_allocate_frame(&none->error_callback, scratch, 500, 1) == 0);
CHECK(secp256k1_scratch_max_allocation(&none->error_callback, scratch, 0) == 1000 - adj_alloc);
CHECK(secp256k1_scratch_max_allocation(&none->error_callback, scratch, 1) == 1000 - adj_alloc - (ALIGNMENT - 1));
CHECK(scratch->alloc_size != 0);
CHECK(scratch->alloc_size % ALIGNMENT == 0);

/* ...and this effect is undone by popping the frame */
secp256k1_scratch_deallocate_frame(&none->error_callback, scratch);
CHECK(secp256k1_scratch_max_allocation(&none->error_callback, scratch, 0) == 1000);
/* Allocating another 500 bytes fails */
CHECK(secp256k1_scratch_alloc(&none->error_callback, scratch, 500) == NULL);
CHECK(secp256k1_scratch_max_allocation(&none->error_callback, scratch, 0) == 1000 - adj_alloc);
CHECK(secp256k1_scratch_max_allocation(&none->error_callback, scratch, 1) == 1000 - adj_alloc - (ALIGNMENT - 1));
CHECK(scratch->alloc_size != 0);
CHECK(scratch->alloc_size % ALIGNMENT == 0);

/* ...but it succeeds once we apply the checkpoint to undo it */
secp256k1_scratch_apply_checkpoint(&none->error_callback, scratch, checkpoint);
CHECK(scratch->alloc_size == 0);
CHECK(secp256k1_scratch_max_allocation(&none->error_callback, scratch, 0) == 1000);
CHECK(secp256k1_scratch_alloc(&none->error_callback, scratch, 500) != NULL);
CHECK(scratch->alloc_size != 0);

/* cleanup */
secp256k1_scratch_space_destroy(none, scratch);
/* try to apply a bad checkpoint */
checkpoint_2 = secp256k1_scratch_checkpoint(&none->error_callback, scratch);
secp256k1_scratch_apply_checkpoint(&none->error_callback, scratch, checkpoint);
CHECK(ecount == 0);
secp256k1_scratch_apply_checkpoint(&none->error_callback, scratch, checkpoint_2); /* checkpoint_2 is after checkpoint */
CHECK(ecount == 1);
secp256k1_scratch_apply_checkpoint(&none->error_callback, scratch, (size_t) -1); /* this is just wildly invalid */
CHECK(ecount == 2);

/* try to use badly initialized scratch space */
secp256k1_scratch_space_destroy(none, scratch);
memset(&local_scratch, 0, sizeof(local_scratch));
scratch = &local_scratch;
CHECK(!secp256k1_scratch_max_allocation(&none->error_callback, scratch, 0));
CHECK(ecount == 1);
CHECK(secp256k1_scratch_allocate_frame(&none->error_callback, scratch, 500, 1) == 0);
CHECK(ecount == 2);
CHECK(secp256k1_scratch_alloc(&none->error_callback, scratch, 500) == NULL);
CHECK(ecount == 3);
secp256k1_scratch_deallocate_frame(&none->error_callback, scratch);
CHECK(secp256k1_scratch_alloc(&none->error_callback, scratch, 500) == NULL);
CHECK(ecount == 4);
secp256k1_scratch_space_destroy(none, scratch);
CHECK(ecount == 5);

/* cleanup */
secp256k1_scratch_space_destroy(none, NULL); /* no-op */
secp256k1_context_destroy(none);
}

Expand Down Expand Up @@ -2946,16 +2961,26 @@ void test_ecmult_multi_pippenger_max_points(void) {
int bucket_window = 0;

for(; scratch_size < max_size; scratch_size+=256) {
size_t i;
size_t total_alloc;
size_t checkpoint;
scratch = secp256k1_scratch_create(&ctx->error_callback, scratch_size);
CHECK(scratch != NULL);
checkpoint = secp256k1_scratch_checkpoint(&ctx->error_callback, scratch);
n_points_supported = secp256k1_pippenger_max_points(&ctx->error_callback, scratch);
if (n_points_supported == 0) {
secp256k1_scratch_destroy(&ctx->error_callback, scratch);
continue;
}
bucket_window = secp256k1_pippenger_bucket_window(n_points_supported);
CHECK(secp256k1_scratch_allocate_frame(&ctx->error_callback, scratch, secp256k1_pippenger_scratch_size(n_points_supported, bucket_window), PIPPENGER_SCRATCH_OBJECTS));
secp256k1_scratch_deallocate_frame(&ctx->error_callback, scratch);
/* allocate `total_alloc` bytes over `PIPPENGER_SCRATCH_OBJECTS` many allocations */
total_alloc = secp256k1_pippenger_scratch_size(n_points_supported, bucket_window);
for (i = 0; i < PIPPENGER_SCRATCH_OBJECTS - 1; i++) {
CHECK(secp256k1_scratch_alloc(&ctx->error_callback, scratch, 1));
total_alloc--;
}
CHECK(secp256k1_scratch_alloc(&ctx->error_callback, scratch, total_alloc));
secp256k1_scratch_apply_checkpoint(&ctx->error_callback, scratch, checkpoint);
secp256k1_scratch_destroy(&ctx->error_callback, scratch);
}
CHECK(bucket_window == PIPPENGER_MAX_BUCKET_WINDOW);
Expand Down

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