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extrakeys: add secp256k1_pubkey_sort
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jonasnick committed Jan 23, 2024
1 parent e4af41c commit 26dde29
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15 changes: 15 additions & 0 deletions include/secp256k1_extrakeys.h
Original file line number Diff line number Diff line change
Expand Up @@ -240,6 +240,21 @@ SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_keypair_xonly_tweak_add
const unsigned char *tweak32
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);

/** Sort public keys using lexicographic order of their compressed
* serialization.
*
* Returns: 0 if the arguments are invalid. 1 otherwise.
*
* Args: ctx: pointer to a context object
* In: pubkeys: array of pointers to pubkeys to sort
* n_pubkeys: number of elements in the pubkeys array
*/
SECP256K1_API int secp256k1_pubkey_sort(
const secp256k1_context *ctx,
const secp256k1_pubkey **pubkeys,
size_t n_pubkeys
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2);

#ifdef __cplusplus
}
#endif
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2 changes: 2 additions & 0 deletions src/modules/extrakeys/Makefile.am.include
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Expand Up @@ -2,3 +2,5 @@ include_HEADERS += include/secp256k1_extrakeys.h
noinst_HEADERS += src/modules/extrakeys/tests_impl.h
noinst_HEADERS += src/modules/extrakeys/tests_exhaustive_impl.h
noinst_HEADERS += src/modules/extrakeys/main_impl.h
noinst_HEADERS += src/modules/extrakeys/hsort.h
noinst_HEADERS += src/modules/extrakeys/hsort_impl.h
22 changes: 22 additions & 0 deletions src/modules/extrakeys/hsort.h
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@@ -0,0 +1,22 @@
/***********************************************************************
* Copyright (c) 2021 Russell O'Connor, Jonas Nick *
* Distributed under the MIT software license, see the accompanying *
* file COPYING or https://www.opensource.org/licenses/mit-license.php.*
***********************************************************************/

#ifndef SECP256K1_HSORT_H
#define SECP256K1_HSORT_H

#include <stddef.h>
#include <string.h>

/* In-place, iterative heapsort with an interface matching glibc's qsort_r. This
* is preferred over standard library implementations because they generally
* make no guarantee about being fast for malicious inputs.
*
* See the qsort_r manpage for a description of the interface.
*/
static void secp256k1_hsort(void *ptr, size_t count, size_t size,
int (*cmp)(const void *, const void *, void *),
void *cmp_data);
#endif
116 changes: 116 additions & 0 deletions src/modules/extrakeys/hsort_impl.h
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@@ -0,0 +1,116 @@
/***********************************************************************
* Copyright (c) 2021 Russell O'Connor, Jonas Nick *
* Distributed under the MIT software license, see the accompanying *
* file COPYING or https://www.opensource.org/licenses/mit-license.php.*
***********************************************************************/

#ifndef SECP256K1_HSORT_IMPL_H
#define SECP256K1_HSORT_IMPL_H

#include "hsort.h"

/* An array is a heap when, for all non-zero indexes i, the element at index i
* compares as less than or equal to the element at index parent(i) = (i-1)/2.
*/

static SECP256K1_INLINE size_t child1(size_t i) {
VERIFY_CHECK(i <= (SIZE_MAX - 1)/2);
return 2*i + 1;
}

static SECP256K1_INLINE size_t child2(size_t i) {
VERIFY_CHECK(i <= SIZE_MAX/2 - 1);
return child1(i)+1;
}

static SECP256K1_INLINE void heap_swap64(unsigned char *a, size_t i, size_t j, size_t stride) {
unsigned char tmp[64];
VERIFY_CHECK(stride <= 64);
memcpy(tmp, a + i*stride, stride);
memmove(a + i*stride, a + j*stride, stride);
memcpy(a + j*stride, tmp, stride);
}

static SECP256K1_INLINE void heap_swap(unsigned char *a, size_t i, size_t j, size_t stride) {
while (64 < stride) {
heap_swap64(a + (stride - 64), i, j, 64);
stride -= 64;
}
heap_swap64(a, i, j, stride);
}

static SECP256K1_INLINE void heap_down(unsigned char *a, size_t i, size_t heap_size, size_t stride,
int (*cmp)(const void *, const void *, void *), void *cmp_data) {
while (i < heap_size/2) {
VERIFY_CHECK(i <= SIZE_MAX/2 - 1);
/* Proof:
* i < heap_size/2
* i + 1 <= heap_size/2
* 2*i + 2 <= heap_size <= SIZE_MAX
* 2*i <= SIZE_MAX - 2
*/

VERIFY_CHECK(child1(i) < heap_size);
/* Proof:
* i < heap_size/2
* i + 1 <= heap_size/2
* 2*i + 2 <= heap_size
* 2*i + 1 < heap_size
* child1(i) < heap_size
*/

/* Let [x] be notation for the contents at a[x*stride].
*
* If [child1(i)] > [i] and [child2(i)] > [i],
* swap [i] with the larger child to ensure the new parent is larger
* than both children. When [child1(i)] == [child2(i)], swap [i] with
* [child2(i)].
* Else if [child1(i)] > [i], swap [i] with [child1(i)].
* Else if [child2(i)] > [i], swap [i] with [child2(i)].
*/
if (child2(i) < heap_size
&& 0 <= cmp(a + child2(i)*stride, a + child1(i)*stride, cmp_data)) {
if (0 < cmp(a + child2(i)*stride, a + i*stride, cmp_data)) {
heap_swap(a, i, child2(i), stride);
i = child2(i);
} else {
/* At this point we have [child2(i)] >= [child1(i)] and we have
* [child2(i)] <= [i], and thus [child1(i)] <= [i] which means
* that the next comparison can be skipped. */
return;
}
} else if (0 < cmp(a + child1(i)*stride, a + i*stride, cmp_data)) {
heap_swap(a, i, child1(i), stride);
i = child1(i);
} else {
return;
}
}
/* heap_size/2 <= i
* heap_size/2 < i + 1
* heap_size < 2*i + 2
* heap_size <= 2*i + 1
* heap_size <= child1(i)
* Thus child1(i) and child2(i) are now out of bounds and we are at a leaf.
*/
}

/* In-place heap sort. */
static void secp256k1_hsort(void *ptr, size_t count, size_t size,
int (*cmp)(const void *, const void *, void *),
void *cmp_data ) {
size_t i;

for(i = count/2; 0 < i; --i) {
heap_down(ptr, i-1, count, size, cmp, cmp_data);
}
for(i = count; 1 < i; --i) {
/* Extract the largest value from the heap */
heap_swap(ptr, 0, i-1, size);

/* Repair the heap condition */
heap_down(ptr, 0, i-1, size, cmp, cmp_data);
}
}

#endif
35 changes: 35 additions & 0 deletions src/modules/extrakeys/main_impl.h
Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,7 @@

#include "../../../include/secp256k1.h"
#include "../../../include/secp256k1_extrakeys.h"
#include "hsort_impl.h"
#include "../../util.h"

static SECP256K1_INLINE int secp256k1_xonly_pubkey_load(const secp256k1_context* ctx, secp256k1_ge *ge, const secp256k1_xonly_pubkey *pubkey) {
Expand Down Expand Up @@ -282,4 +283,38 @@ int secp256k1_keypair_xonly_tweak_add(const secp256k1_context* ctx, secp256k1_ke
return ret;
}

/* This struct wraps a const context pointer to satisfy the secp256k1_hsort api
* which expects a non-const cmp_data pointer. */
typedef struct {
const secp256k1_context *ctx;
} secp256k1_pubkey_sort_cmp_data;

static int secp256k1_pubkey_sort_cmp(const void* pk1, const void* pk2, void *cmp_data) {
return secp256k1_ec_pubkey_cmp(((secp256k1_pubkey_sort_cmp_data*)cmp_data)->ctx,
*(secp256k1_pubkey **)pk1,
*(secp256k1_pubkey **)pk2);
}

int secp256k1_pubkey_sort(const secp256k1_context* ctx, const secp256k1_pubkey **pubkeys, size_t n_pubkeys) {
secp256k1_pubkey_sort_cmp_data cmp_data;
VERIFY_CHECK(ctx != NULL);
ARG_CHECK(pubkeys != NULL);

cmp_data.ctx = ctx;

/* Suppress wrong warning (fixed in MSVC 19.33) */
#if defined(_MSC_VER) && (_MSC_VER < 1933)
#pragma warning(push)
#pragma warning(disable: 4090)
#endif

secp256k1_hsort(pubkeys, n_pubkeys, sizeof(*pubkeys), secp256k1_pubkey_sort_cmp, &cmp_data);

#if defined(_MSC_VER) && (_MSC_VER < 1933)
#pragma warning(pop)
#endif

return 1;
}

#endif
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