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patch 8.1.2343: using time() for srand() is not very random

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Problem:    Using time() for srand() is not very random.
Solution:   use /dev/urandom if available
This commit is contained in:
Bram Moolenaar
2019-11-26 12:23:30 +01:00
parent 06b0b4bc27
commit 07e4a19795
3 changed files with 50 additions and 5 deletions
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39
src/evalfunc.c
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@@ -7095,10 +7095,45 @@ f_sqrt(typval_T *argvars, typval_T *rettv)
static void
f_srand(typval_T *argvars, typval_T *rettv)
{
static int dev_urandom_state = -1; // FAIL or OK once tried
if (rettv_list_alloc(rettv) == FAIL)
return;
if (argvars[0].v_type == VAR_UNKNOWN)
list_append_number(rettv->vval.v_list, (varnumber_T)vim_time());
{
if (dev_urandom_state != FAIL)
{
int fd = open("/dev/urandom", O_RDONLY);
struct {
union {
UINT32_T number;
char bytes[sizeof(UINT32_T)];
} cont;
} buf;
// Attempt reading /dev/urandom.
if (fd == -1)
dev_urandom_state = FAIL;
else
{
buf.cont.number = 0;
if (read(fd, buf.cont.bytes, sizeof(UINT32_T))
!= sizeof(UINT32_T))
dev_urandom_state = FAIL;
else
{
dev_urandom_state = OK;
list_append_number(rettv->vval.v_list,
(varnumber_T)buf.cont.number);
}
close(fd);
}
}
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());
}
else
{
int error = FALSE;
@@ -7107,7 +7142,7 @@ f_srand(typval_T *argvars, typval_T *rettv)
if (error)
return;
list_append_number(rettv->vval.v_list, x);
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);