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patch 8.1.2356: rand() does not use the best algorithm

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Problem:    rand() does not use the best algorithm.
Solution:   use xoshiro128** instead of xorshift. (Kaito Udagawa,
            closes #5279)
This commit is contained in:
Bram Moolenaar
2019-11-28 22:13:14 +01:00
parent c7d2a57b3a
commit f8c1f9200c
4 changed files with 80 additions and 67 deletions
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14
runtime/doc/eval.txt
View File

@@ -1,4 +1,4 @@
*eval.txt* For Vim version 8.1. Last change: 2019 Nov 25
*eval.txt* For Vim version 8.1. Last change: 2019 Nov 28
VIM REFERENCE MANUAL by Bram Moolenaar
@@ -7641,7 +7641,7 @@ range({expr} [, {max} [, {stride}]]) *range()*
<
rand([{expr}]) *rand()*
Return a pseudo-random Number generated with an xorshift
Return a pseudo-random Number generated with an xoshiro128**
algorithm using seed {expr}. The returned number is 32 bits,
also on 64 bits systems, for consistency.
{expr} can be initialized by |srand()| and will be updated by
@@ -9150,11 +9150,11 @@ sqrt({expr}) *sqrt()*
srand([{expr}]) *srand()*
Initialize seed used by |rand()|:
- If {expr} is not given, seed values are initialized by
time(NULL) a.k.a. epoch time. This only has second
accuracy.
- If {expr} is given, return seed values which x element is
{expr}. This is useful for testing or when a predictable
sequence is expected.
reading from /dev/urandom, if possible, or using time(NULL)
a.k.a. epoch time otherwise; this only has second accuracy.
- If {expr} is given it must be a Number. It is used to
initialize the seed values. This is useful for testing or
when a predictable sequence is intended.
Examples: >
:let seed = srand()

119
src/evalfunc.c
View File

@@ -5139,70 +5139,74 @@ f_pyxeval(typval_T *argvars, typval_T *rettv)
f_rand(typval_T *argvars, typval_T *rettv)
{
list_T *l = NULL;
UINT32_T x, y, z, w, t;
static int rand_seed_initialized = FALSE;
static UINT32_T xyzw[4] = {123456789, 362436069, 521288629, 88675123};
#define SHUFFLE_XORSHIFT128 \
t = x ^ (x << 11); \
x = y; y = z; z = w; \
w = (w ^ (w >> 19)) ^ (t ^ (t >> 8));
static list_T *globl = NULL;
UINT32_T x, y, z, w, t, result;
listitem_T *lx, *ly, *lz, *lw;
if (argvars[0].v_type == VAR_UNKNOWN)
{
// When argument is not given, return random number initialized
// statically.
if (!rand_seed_initialized)
// When no argument is given use the global seed list.
if (globl == NULL)
{
xyzw[0] = (varnumber_T)time(NULL);
rand_seed_initialized = TRUE;
// Initialize the global seed list.
f_srand(argvars, rettv);
l = rettv->vval.v_list;
if (l == NULL || list_len(l) != 4)
{
clear_tv(rettv);
goto theend;
}
globl = l;
}
x = xyzw[0];
y = xyzw[1];
z = xyzw[2];
w = xyzw[3];
SHUFFLE_XORSHIFT128;
xyzw[0] = x;
xyzw[1] = y;
xyzw[2] = z;
xyzw[3] = w;
else
l = globl;
}
else if (argvars[0].v_type == VAR_LIST)
{
listitem_T *lx, *ly, *lz, *lw;
l = argvars[0].vval.v_list;
if (list_len(l) != 4)
if (l == NULL || list_len(l) != 4)
goto theend;
lx = list_find(l, 0L);
ly = list_find(l, 1L);
lz = list_find(l, 2L);
lw = list_find(l, 3L);
if (lx->li_tv.v_type != VAR_NUMBER) goto theend;
if (ly->li_tv.v_type != VAR_NUMBER) goto theend;
if (lz->li_tv.v_type != VAR_NUMBER) goto theend;
if (lw->li_tv.v_type != VAR_NUMBER) goto theend;
x = (UINT32_T)lx->li_tv.vval.v_number;
y = (UINT32_T)ly->li_tv.vval.v_number;
z = (UINT32_T)lz->li_tv.vval.v_number;
w = (UINT32_T)lw->li_tv.vval.v_number;
SHUFFLE_XORSHIFT128;
lx->li_tv.vval.v_number = (varnumber_T)x;
ly->li_tv.vval.v_number = (varnumber_T)y;
lz->li_tv.vval.v_number = (varnumber_T)z;
lw->li_tv.vval.v_number = (varnumber_T)w;
}
else
goto theend;
lx = list_find(l, 0L);
ly = list_find(l, 1L);
lz = list_find(l, 2L);
lw = list_find(l, 3L);
if (lx->li_tv.v_type != VAR_NUMBER) goto theend;
if (ly->li_tv.v_type != VAR_NUMBER) goto theend;
if (lz->li_tv.v_type != VAR_NUMBER) goto theend;
if (lw->li_tv.v_type != VAR_NUMBER) goto theend;
x = (UINT32_T)lx->li_tv.vval.v_number;
y = (UINT32_T)ly->li_tv.vval.v_number;
z = (UINT32_T)lz->li_tv.vval.v_number;
w = (UINT32_T)lw->li_tv.vval.v_number;
// SHUFFLE_XOSHIRO128STARSTAR
#define ROTL(x, k) ((x << k) | (x >> (32 - k)))
result = ROTL(y * 5, 7) * 9;
t = y << 9;
z ^= x;
w ^= y;
y ^= z, x ^= w;
z ^= t;
w = ROTL(w, 11);
#undef ROTL
lx->li_tv.vval.v_number = (varnumber_T)x;
ly->li_tv.vval.v_number = (varnumber_T)y;
lz->li_tv.vval.v_number = (varnumber_T)z;
lw->li_tv.vval.v_number = (varnumber_T)w;
rettv->v_type = VAR_NUMBER;
rettv->vval.v_number = (varnumber_T)w;
rettv->vval.v_number = (varnumber_T)result;
return;
theend:
semsg(_(e_invarg2), tv_get_string(&argvars[0]));
rettv->v_type = VAR_NUMBER;
rettv->vval.v_number = -1;
}
/*
@@ -7096,6 +7100,7 @@ f_sqrt(typval_T *argvars, typval_T *rettv)
f_srand(typval_T *argvars, typval_T *rettv)
{
static int dev_urandom_state = -1; // FAIL or OK once tried
UINT32_T x = 0, z;
if (rettv_list_alloc(rettv) == FAIL)
return;
@@ -7123,8 +7128,7 @@ f_srand(typval_T *argvars, typval_T *rettv)
else
{
dev_urandom_state = OK;
list_append_number(rettv->vval.v_list,
(varnumber_T)buf.cont.number);
x = buf.cont.number;
}
close(fd);
}
@@ -7132,21 +7136,28 @@ f_srand(typval_T *argvars, typval_T *rettv)
}
if (dev_urandom_state != OK)
// Reading /dev/urandom doesn't work, fall back to time().
list_append_number(rettv->vval.v_list, (varnumber_T)vim_time());
x = vim_time();
}
else
{
int error = FALSE;
UINT32_T x = (UINT32_T)tv_get_number_chk(&argvars[0], &error);
x = (UINT32_T)tv_get_number_chk(&argvars[0], &error);
if (error)
return;
list_append_number(rettv->vval.v_list, (varnumber_T)x);
}
list_append_number(rettv->vval.v_list, 362436069);
list_append_number(rettv->vval.v_list, 521288629);
list_append_number(rettv->vval.v_list, 88675123);
#define SPLITMIX32 ( \
z = (x += 0x9e3779b9), \
z = (z ^ (z >> 16)) * 0x85ebca6b, \
z = (z ^ (z >> 13)) * 0xc2b2ae35, \
z ^ (z >> 16) \
)
list_append_number(rettv->vval.v_list, (varnumber_T)SPLITMIX32);
list_append_number(rettv->vval.v_list, (varnumber_T)SPLITMIX32);
list_append_number(rettv->vval.v_list, (varnumber_T)SPLITMIX32);
list_append_number(rettv->vval.v_list, (varnumber_T)SPLITMIX32);
}
/*

12
src/testdir/test_random.vim
View File

@@ -2,12 +2,12 @@
func Test_Rand()
let r = srand(123456789)
call assert_equal([123456789, 362436069, 521288629, 88675123], r)
call assert_equal(3701687786, rand(r))
call assert_equal(458299110, rand(r))
call assert_equal(2500872618, rand(r))
call assert_equal(3633119408, rand(r))
call assert_equal(516391518, rand(r))
call assert_equal([1573771921, 319883699, 2742014374, 1324369493], r)
call assert_equal(4284103975, rand(r))
call assert_equal(1001954530, rand(r))
call assert_equal(2701803082, rand(r))
call assert_equal(2658065534, rand(r))
call assert_equal(3104308804, rand(r))
call test_settime(12341234)
let s = srand()

2
src/version.c
View File

@@ -737,6 +737,8 @@ static char *(features[]) =
static int included_patches[] =
{ /* Add new patch number below this line */
/**/
2356,
/**/
2355,
/**/