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common: add tal_arr_randomize() to shuffle an array.

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Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
This commit is contained in:
Rusty Russell 2023-08-11 12:34:47 +09:30
parent 846cec4f2a
commit 66a5765725
3 changed files with 226 additions and 0 deletions
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29
common/pseudorand.c
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@ -4,6 +4,7 @@
#include <ccan/crypto/siphash24/siphash24.h>
#include <ccan/isaac/isaac64.h>
#include <ccan/likely/likely.h>
#include <ccan/tal/tal.h>
#include <common/pseudorand.h>
#include <sodium/randombytes.h>
#include <string.h>
@ -56,3 +57,31 @@ const struct siphash_seed *siphash_seed(void)
return &siphashseed;
}
void tal_arr_randomize_(void *arr, size_t elemsize)
{
/* Easier arith. */
char *carr = arr;
size_t n = tal_bytelen(arr) / elemsize;
assert(tal_bytelen(arr) % elemsize == 0);
/* From Wikipedia's Fischer-Yates shuffle article:
*
* for i from 0 to n−2 do
* j ← random integer such that i ≤ j < n
* exchange a[i] and a[j]
*/
if (n < 2)
return;
for (size_t i = 0; i < n - 1; i++) {
size_t j = i + pseudorand(n - i);
char tmp[elemsize];
memcpy(tmp, carr + i * elemsize, elemsize);
memcpy(carr + i * elemsize, carr + j * elemsize, elemsize);
memcpy(carr + j * elemsize, tmp, elemsize);
}
}

6
common/pseudorand.h
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@ -2,6 +2,7 @@
#define LIGHTNING_COMMON_PSEUDORAND_H
#include "config.h"
#include <stdint.h>
#include <stdlib.h>
/**
* pseudorand - pseudo (guessable!) random number between 0 and max-1.
@ -24,4 +25,9 @@ double pseudorand_double(void);
*/
const struct siphash_seed *siphash_seed(void);
/* Shuffle a tal array of type type. */
#define tal_arr_randomize(arr, type) \
tal_arr_randomize_((arr), sizeof(type) + 0*sizeof(arr == (type *)NULL))
void tal_arr_randomize_(void *arr, size_t elemsize);
#endif /* LIGHTNING_COMMON_PSEUDORAND_H */

191
common/test/run-tal_arr_randomize.c Normal file
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@ -0,0 +1,191 @@
#include "config.h"
#include "../pseudorand.c"
#include <ccan/array_size/array_size.h>
#include <common/amount.h>
#include <common/setup.h>
#include <common/utils.h>
#include <stdio.h>
#include <wire/wire.h>
/* AUTOGENERATED MOCKS START */
/* Generated stub for amount_asset_is_main */
bool amount_asset_is_main(struct amount_asset *asset UNNEEDED)
{ fprintf(stderr, "amount_asset_is_main called!\n"); abort(); }
/* Generated stub for amount_asset_to_sat */
struct amount_sat amount_asset_to_sat(struct amount_asset *asset UNNEEDED)
{ fprintf(stderr, "amount_asset_to_sat called!\n"); abort(); }
/* Generated stub for amount_sat */
struct amount_sat amount_sat(u64 satoshis UNNEEDED)
{ fprintf(stderr, "amount_sat called!\n"); abort(); }
/* Generated stub for amount_sat_add */
bool amount_sat_add(struct amount_sat *val UNNEEDED,
struct amount_sat a UNNEEDED,
struct amount_sat b UNNEEDED)
{ fprintf(stderr, "amount_sat_add called!\n"); abort(); }
/* Generated stub for amount_sat_div */
struct amount_sat amount_sat_div(struct amount_sat sat UNNEEDED, u64 div UNNEEDED)
{ fprintf(stderr, "amount_sat_div called!\n"); abort(); }
/* Generated stub for amount_sat_eq */
bool amount_sat_eq(struct amount_sat a UNNEEDED, struct amount_sat b UNNEEDED)
{ fprintf(stderr, "amount_sat_eq called!\n"); abort(); }
/* Generated stub for amount_sat_greater_eq */
bool amount_sat_greater_eq(struct amount_sat a UNNEEDED, struct amount_sat b UNNEEDED)
{ fprintf(stderr, "amount_sat_greater_eq called!\n"); abort(); }
/* Generated stub for amount_sat_mul */
bool amount_sat_mul(struct amount_sat *res UNNEEDED, struct amount_sat sat UNNEEDED, u64 mul UNNEEDED)
{ fprintf(stderr, "amount_sat_mul called!\n"); abort(); }
/* Generated stub for amount_sat_sub */
bool amount_sat_sub(struct amount_sat *val UNNEEDED,
struct amount_sat a UNNEEDED,
struct amount_sat b UNNEEDED)
{ fprintf(stderr, "amount_sat_sub called!\n"); abort(); }
/* Generated stub for amount_sat_to_asset */
struct amount_asset amount_sat_to_asset(struct amount_sat *sat UNNEEDED, const u8 *asset UNNEEDED)
{ fprintf(stderr, "amount_sat_to_asset called!\n"); abort(); }
/* Generated stub for amount_tx_fee */
struct amount_sat amount_tx_fee(u32 fee_per_kw UNNEEDED, size_t weight UNNEEDED)
{ fprintf(stderr, "amount_tx_fee called!\n"); abort(); }
/* Generated stub for fromwire */
const u8 *fromwire(const u8 **cursor UNNEEDED, size_t *max UNNEEDED, void *copy UNNEEDED, size_t n UNNEEDED)
{ fprintf(stderr, "fromwire called!\n"); abort(); }
/* Generated stub for fromwire_bool */
bool fromwire_bool(const u8 **cursor UNNEEDED, size_t *max UNNEEDED)
{ fprintf(stderr, "fromwire_bool called!\n"); abort(); }
/* Generated stub for fromwire_fail */
void *fromwire_fail(const u8 **cursor UNNEEDED, size_t *max UNNEEDED)
{ fprintf(stderr, "fromwire_fail called!\n"); abort(); }
/* Generated stub for fromwire_secp256k1_ecdsa_signature */
void fromwire_secp256k1_ecdsa_signature(const u8 **cursor UNNEEDED, size_t *max UNNEEDED,
secp256k1_ecdsa_signature *signature UNNEEDED)
{ fprintf(stderr, "fromwire_secp256k1_ecdsa_signature called!\n"); abort(); }
/* Generated stub for fromwire_sha256 */
void fromwire_sha256(const u8 **cursor UNNEEDED, size_t *max UNNEEDED, struct sha256 *sha256 UNNEEDED)
{ fprintf(stderr, "fromwire_sha256 called!\n"); abort(); }
/* Generated stub for fromwire_tal_arrn */
u8 *fromwire_tal_arrn(const tal_t *ctx UNNEEDED,
const u8 **cursor UNNEEDED, size_t *max UNNEEDED, size_t num UNNEEDED)
{ fprintf(stderr, "fromwire_tal_arrn called!\n"); abort(); }
/* Generated stub for fromwire_u32 */
u32 fromwire_u32(const u8 **cursor UNNEEDED, size_t *max UNNEEDED)
{ fprintf(stderr, "fromwire_u32 called!\n"); abort(); }
/* Generated stub for fromwire_u64 */
u64 fromwire_u64(const u8 **cursor UNNEEDED, size_t *max UNNEEDED)
{ fprintf(stderr, "fromwire_u64 called!\n"); abort(); }
/* Generated stub for fromwire_u8 */
u8 fromwire_u8(const u8 **cursor UNNEEDED, size_t *max UNNEEDED)
{ fprintf(stderr, "fromwire_u8 called!\n"); abort(); }
/* Generated stub for fromwire_u8_array */
void fromwire_u8_array(const u8 **cursor UNNEEDED, size_t *max UNNEEDED, u8 *arr UNNEEDED, size_t num UNNEEDED)
{ fprintf(stderr, "fromwire_u8_array called!\n"); abort(); }
/* Generated stub for towire */
void towire(u8 **pptr UNNEEDED, const void *data UNNEEDED, size_t len UNNEEDED)
{ fprintf(stderr, "towire called!\n"); abort(); }
/* Generated stub for towire_bool */
void towire_bool(u8 **pptr UNNEEDED, bool v UNNEEDED)
{ fprintf(stderr, "towire_bool called!\n"); abort(); }
/* Generated stub for towire_secp256k1_ecdsa_signature */
void towire_secp256k1_ecdsa_signature(u8 **pptr UNNEEDED,
const secp256k1_ecdsa_signature *signature UNNEEDED)
{ fprintf(stderr, "towire_secp256k1_ecdsa_signature called!\n"); abort(); }
/* Generated stub for towire_sha256 */
void towire_sha256(u8 **pptr UNNEEDED, const struct sha256 *sha256 UNNEEDED)
{ fprintf(stderr, "towire_sha256 called!\n"); abort(); }
/* Generated stub for towire_u32 */
void towire_u32(u8 **pptr UNNEEDED, u32 v UNNEEDED)
{ fprintf(stderr, "towire_u32 called!\n"); abort(); }
/* Generated stub for towire_u64 */
void towire_u64(u8 **pptr UNNEEDED, u64 v UNNEEDED)
{ fprintf(stderr, "towire_u64 called!\n"); abort(); }
/* Generated stub for towire_u8 */
void towire_u8(u8 **pptr UNNEEDED, u8 v UNNEEDED)
{ fprintf(stderr, "towire_u8 called!\n"); abort(); }
/* Generated stub for towire_u8_array */
void towire_u8_array(u8 **pptr UNNEEDED, const u8 *arr UNNEEDED, size_t num UNNEEDED)
{ fprintf(stderr, "towire_u8_array called!\n"); abort(); }
/* AUTOGENERATED MOCKS END */
static bool any_equal(const char **arr, size_t n)
{
for (size_t i = 0; i < n; i++) {
for (size_t j = i+1; j < n; j++) {
if (arr[i] == arr[j])
return true;
}
}
return false;
}
static bool one_of(const char **arr, size_t n, const char *word)
{
for (size_t i = 0; i < n; i++) {
if (word == arr[i])
return true;
}
return false;
}
int main(int argc, char *argv[])
{
const char *words[] = {
"hello",
"world",
"this",
"is",
"a",
"pay_test",
"with",
"many",
"elements",
"so",
"the",
"chances",
"of",
"it",
"remaining",
"unshuffled",
"are",
"insignficant",
"and",
"we",
"expect",
"almost",
"every",
"word",
"to",
"be",
"in",
"some",
"different",
"place",
"after",
"shuffling."
};
common_setup(argv[0]);
for (size_t i = 0; i < ARRAY_SIZE(words); i++) {
const char **arr = tal_arr(tmpctx, const char *, i);
memcpy(arr, words, tal_bytelen(arr));
tal_arr_randomize(arr, const char *);
/* They should all point to distinct words */
assert(!any_equal(arr, i));
/* They should point to our expected words. */
for (size_t j = 0; j < i; j++)
assert(one_of(words, i, arr[j]));
/* It will actually shuffle! */
if (i == ARRAY_SIZE(words) - 1) {
size_t num_same = 0;
for (size_t j = 0; j < i; j++) {
printf("%s ", arr[j]);
if (arr[j] == words[j])
num_same++;
}
assert(num_same < i/2);
printf("\n%zu\n", num_same);
}
}
common_shutdown();
return 0;
}