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lavu/eval: add randomi function to compute random value in interval

This commit is contained in:
Stefano Sabatini 2023-12-28 19:09:22 +01:00
parent 933c7ff0b9
commit 7769afcab4
3 changed files with 29 additions and 10 deletions
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1
Changelog
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@ -15,6 +15,7 @@ version <next>:
- tiltandshift filter
- qrencode filter and qrencodesrc source
- quirc filter
- lavu/eval: introduce randomi() function in expressions
version 6.1:
- libaribcaption decoder

12
doc/utils.texi
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@ -939,9 +939,15 @@ Returns the value of the expression printed.
Prints t with loglevel l
@item random(x)
Return a pseudo random value between 0.0 and 1.0. @var{x} is the index of the
internal variable which will be used to save the seed/state.
@item random(idx)
Return a pseudo random value between 0.0 and 1.0. @var{idx} is the
index of the internal variable which will be used to save the
seed/state.
@item randomi(idx, min, max)
Return a pseudo random value in the interval between @var{min} and
@var{max}. @var{idx} is the index of the internal variable which will
be used to save the seed/state.
@item root(expr, max)
Find an input value for which the function represented by @var{expr}

26
libavutil/eval.c
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@ -162,7 +162,7 @@ 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;
@ -228,12 +228,22 @@ static double eval_expr(Parser *p, AVExpr *e)
av_log(p, level, "%f\n", x);
return x;
}
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;
p->var[idx]= r;
return e->value * (r * (1.0/UINT64_MAX));
#define COMPUTE_NEXT_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; \
p->var[idx] = r; \
case e_random: {
COMPUTE_NEXT_RANDOM();
return r * (1.0/UINT64_MAX);
}
case e_randomi: {
double min = eval_expr(p, e->param[1]);
double max = eval_expr(p, e->param[2]);
COMPUTE_NEXT_RANDOM();
return min + (max - min) * r / UINT64_MAX;
}
case e_while: {
double d = NAN;
@ -461,6 +471,7 @@ 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;
@ -674,6 +685,7 @@ 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]);