On date Thursday 2023-12-28 16:00:57 +0100, Stefano Sabatini wrote:
> On date Thursday 2023-12-28 12:02:59 +0100, Andreas Rheinhardt wrote:
> > Stefano Sabatini:
> > > This is useful to simulate random jitter.
> > > ---
> > > Changelog | 1 +
> > > doc/filters.texi | 10 +++++++++-
> > > libavfilter/setpts.c | 39 +++++++++++++++++++++++++++++++++------
> > > 3 files changed, 43 insertions(+), 7 deletions(-)
[...]
> > Why is this added here and not in lavu/eval so that it is available with
> > all expressions?
>
> There is no specific reason. Sometimes you need to have a control over
> the seed, in this case you need to provide the PRNG context.
>
> For the general case, probably we can place a global LFG in the eval
> module and fetch its generated values.
Another possible solution in attachment, leveraging the same affine
PRNG used in random(). For other use cases you might need to use a
high-quality PRNG and this might not be good enough.
>From 4dc5213b0913a2585f75dfd03b497ca2efc093de Mon Sep 17 00:00:00 2001
From: Stefano Sabatini <stefa...@gmail.com>
Date: Thu, 28 Dec 2023 19:09:22 +0100
Subject: [PATCH] lavu/eval: add randomi function to compute random value in
interval
---
libavutil/eval.c | 18 +++++++++++++++---
1 file changed, 15 insertions(+), 3 deletions(-)
diff --git a/libavutil/eval.c b/libavutil/eval.c
index 344bebbf69..e94597ccf4 100644
--- a/libavutil/eval.c
+++ b/libavutil/eval.c
@@ -164,7 +164,7 @@ struct AVExpr {
e_last, e_st, e_while, e_taylor, e_root, e_floor, e_ceil, e_trunc, e_round,
e_sqrt, e_not, e_random, e_hypot, e_gcd,
e_if, e_ifnot, e_print, e_bitand, e_bitor, e_between, e_clip, e_atan2, e_lerp,
- e_sgn,
+ e_sgn, e_randomi
} type;
double value; // is sign in other types
int const_index;
@@ -230,13 +230,23 @@ static double eval_expr(Parser *p, AVExpr *e)
av_log(p, level, "%f\n", x);
return x;
}
- case e_random:{
+#define COMPUTE_RANDOM(seed_) (seed_)*1664525+1013904223
+ case e_random:{
int idx= av_clip(eval_expr(p, e->param[0]), 0, VARS-1);
uint64_t r= isnan(p->var[idx]) ? 0 : p->var[idx];
- r= r*1664525+1013904223;
+ r = COMPUTE_RANDOM(r);
p->var[idx]= r;
return e->value * (r * (1.0/UINT64_MAX));
}
+ case e_randomi: {
+ int idx = av_clip(eval_expr(p, e->param[0]), 0, VARS-1);
+ uint64_t r = isnan(p->var[idx]) ? 0 : p->var[idx];
+ r = COMPUTE_RANDOM(r);
+ p->var[idx] = r;
+ double min = eval_expr(p, e->param[1]);
+ double max = eval_expr(p, e->param[2]);
+ return min + (max - min) * r / UINT64_MAX;
+ }
case e_while: {
double d = NAN;
while (eval_expr(p, e->param[0]))
@@ -463,6 +473,7 @@ static int parse_primary(AVExpr **e, Parser *p)
else if (strmatch(next, "pow" )) d->type = e_pow;
else if (strmatch(next, "print" )) d->type = e_print;
else if (strmatch(next, "random")) d->type = e_random;
+ else if (strmatch(next, "randomi")) d->type = e_randomi;
else if (strmatch(next, "hypot" )) d->type = e_hypot;
else if (strmatch(next, "gcd" )) d->type = e_gcd;
else if (strmatch(next, "if" )) d->type = e_if;
@@ -676,6 +687,7 @@ static int verify_expr(AVExpr *e)
case e_between:
case e_clip:
case e_lerp:
+ case e_randomi:
return verify_expr(e->param[0]) &&
verify_expr(e->param[1]) &&
verify_expr(e->param[2]);
--
2.34.1
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