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test-mergesort: use repeatable random numbers 

Use MINSTD to generate pseudo-random numbers consistently instead of
using rand(3), whose output can vary from system to system, and reset
its seed before filling in the test values.  This gives repeatable
results across versions and systems, which simplifies sharing and
comparing of results between developers.

Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
maint
René Scharfe 2021-10-08 06:04:42 +02:00 committed by Junio C Hamano
parent afc72b5d3a
commit c90cfc225b
1 changed files with 10 additions and 2 deletions
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12
t/helper/test-mergesort.c
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@ -2,6 +2,12 @@
#include "cache.h"
#include "mergesort.h"

static uint32_t minstd_rand(uint32_t *state)
{
*state = (uint64_t)*state * 48271 % 2147483647;
return *state;
}

struct line {
char *text;
struct line *next;
@ -60,8 +66,9 @@ static void dist_sawtooth(int *arr, int n, int m)
static void dist_rand(int *arr, int n, int m)
{
int i;
uint32_t seed = 1;
for (i = 0; i < n; i++)
arr[i] = rand() % m;
arr[i] = minstd_rand(&seed) % m;
}

static void dist_stagger(int *arr, int n, int m)
@ -81,8 +88,9 @@ static void dist_plateau(int *arr, int n, int m)
static void dist_shuffle(int *arr, int n, int m)
{
int i, j, k;
uint32_t seed = 1;
for (i = j = 0, k = 1; i < n; i++)
arr[i] = (rand() % m) ? (j += 2) : (k += 2);
arr[i] = minstd_rand(&seed) % m ? (j += 2) : (k += 2);
}

#define DIST(name) { #name, dist_##name }