/*

  * Copyright (c) 2002-2006 Michael Niedermayer <michaelni@gmx.at>

  * Copyright (c) 2006 Oded Shimon <ods15@ods15.dyndns.org>

  *

  * This file is part of FFmpeg.
  *
  * FFmpeg is free software; you can redistribute it and/or

  * modify it under the terms of the GNU Lesser General Public
  * License as published by the Free Software Foundation; either

  * version 2.1 of the License, or (at your option) any later version.

  *

  * FFmpeg is distributed in the hope that it will be useful,

  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Lesser General Public License for more details.
  *
  * You should have received a copy of the GNU Lesser General Public

  * License along with FFmpeg; if not, write to the Free Software

  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA

  */
 

 /**

  * @file

  * simple arithmetic expression evaluator.
  *

  * see http://joe.hotchkiss.com/programming/eval/eval.html
  */
 

 #include <float.h>

 #include "attributes.h"

 #include "avutil.h"

 #include "common.h"

 #include "eval.h"

 #include "ffmath.h"

 #include "internal.h"

 #include "log.h"

 #include "mathematics.h"

 #include "time.h"

 #include "avstring.h"

 #include "timer.h"

 #include "reverse.h"

 typedef struct Parser {

     const AVClass *class;

     int stack_index;
     char *s;

     const double *const_values;
     const char * const *const_names;          // NULL terminated
     double (* const *funcs1)(void *, double a);           // NULL terminated
     const char * const *func1_names;          // NULL terminated
     double (* const *funcs2)(void *, double a, double b); // NULL terminated
     const char * const *func2_names;          // NULL terminated

     void *opaque;

     int log_offset;
     void *log_ctx;

 #define VARS 10

     double *var;

 } Parser;
 

 static const AVClass eval_class = {

     .class_name                = "Eval",
     .item_name                 = av_default_item_name,
     .option                    = NULL,
     .version                   = LIBAVUTIL_VERSION_INT,
     .log_level_offset_offset   = offsetof(Parser, log_offset),
     .parent_log_context_offset = offsetof(Parser, log_ctx),
 };

 static const struct {
     double bin_val;
     double dec_val;
     int8_t exp;
 } si_prefixes['z' - 'E' + 1] = {
     ['y'-'E']= { 8.271806125530276749e-25, 1e-24, -24 },
     ['z'-'E']= { 8.4703294725430034e-22, 1e-21, -21 },
     ['a'-'E']= { 8.6736173798840355e-19, 1e-18, -18 },
     ['f'-'E']= { 8.8817841970012523e-16, 1e-15, -15 },
     ['p'-'E']= { 9.0949470177292824e-13, 1e-12, -12 },
     ['n'-'E']= { 9.3132257461547852e-10, 1e-9,  -9 },
     ['u'-'E']= { 9.5367431640625e-7, 1e-6, -6 },
     ['m'-'E']= { 9.765625e-4, 1e-3, -3 },
     ['c'-'E']= { 9.8431332023036951e-3, 1e-2, -2 },
     ['d'-'E']= { 9.921256574801246e-2, 1e-1, -1 },
     ['h'-'E']= { 1.0159366732596479e2, 1e2, 2 },
     ['k'-'E']= { 1.024e3, 1e3, 3 },
     ['K'-'E']= { 1.024e3, 1e3, 3 },
     ['M'-'E']= { 1.048576e6, 1e6, 6 },
     ['G'-'E']= { 1.073741824e9, 1e9, 9 },
     ['T'-'E']= { 1.099511627776e12, 1e12, 12 },
     ['P'-'E']= { 1.125899906842624e15, 1e15, 15 },
     ['E'-'E']= { 1.152921504606847e18, 1e18, 18 },
     ['Z'-'E']= { 1.1805916207174113e21, 1e21, 21 },
     ['Y'-'E']= { 1.2089258196146292e24, 1e24, 24 },

 };
 

 static const struct {
     const char *name;
     double value;
 } constants[] = {
     { "E",   M_E   },
     { "PI",  M_PI  },
     { "PHI", M_PHI },

     { "QP2LAMBDA", FF_QP2LAMBDA },

 };
 

 double av_strtod(const char *numstr, char **tail)
 {

     double d;
     char *next;

     if(numstr[0]=='0' && (numstr[1]|0x20)=='x') {

         d = strtoul(numstr, &next, 16);

     } else
         d = strtod(numstr, &next);

     /* if parsing succeeded, check for and interpret postfixes */

     if (next!=numstr) {

         if (next[0] == 'd' && next[1] == 'B') {
             /* treat dB as decibels instead of decibytes */

             d = ff_exp10(d / 20);

             next += 2;
         } else if (*next >= 'E' && *next <= 'z') {

             int e= si_prefixes[*next - 'E'].exp;

             if (e) {
                 if (next[1] == 'i') {

                     d*= si_prefixes[*next - 'E'].bin_val;

                     next+=2;

                 } else {

                     d*= si_prefixes[*next - 'E'].dec_val;

                     next++;
                 }
             }
         }
 

         if (*next=='B') {

             d*=8;

             next++;

         }
     }
     /* if requested, fill in tail with the position after the last parsed
        character */
     if (tail)
         *tail = next;
     return d;
 }
 

 #define IS_IDENTIFIER_CHAR(c) ((c) - '0' <= 9U || (c) - 'a' <= 25U || (c) - 'A' <= 25U || (c) == '_')
 

 static int strmatch(const char *s, const char *prefix)
 {

     int i;

     for (i=0; prefix[i]; i++) {
         if (prefix[i] != s[i]) return 0;

     }

     /* return 1 only if the s identifier is terminated */
     return !IS_IDENTIFIER_CHAR(s[i]);

 }
 

 struct AVExpr {

     enum {
         e_value, e_const, e_func0, e_func1, e_func2,

         e_squish, e_gauss, e_ld, e_isnan, e_isinf,

         e_mod, e_max, e_min, e_eq, e_gt, e_gte, e_lte, e_lt,

         e_pow, e_mul, e_div, e_add,

         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,

     } type;
     double value; // is sign in other types
     union {
         int const_index;
         double (*func0)(double);
         double (*func1)(void *, double);
         double (*func2)(void *, double, double);
     } a;

     struct AVExpr *param[3];

     double *var;

 };
 

 static double etime(double v)
 {
     return av_gettime() * 0.000001;
 }
 

 static double eval_expr(Parser *p, AVExpr *e)
 {

     switch (e->type) {
         case e_value:  return e->value;

         case e_const:  return e->value * p->const_values[e->a.const_index];

         case e_func0:  return e->value * e->a.func0(eval_expr(p, e->param[0]));
         case e_func1:  return e->value * e->a.func1(p->opaque, eval_expr(p, e->param[0]));
         case e_func2:  return e->value * e->a.func2(p->opaque, eval_expr(p, e->param[0]), eval_expr(p, e->param[1]));
         case e_squish: return 1/(1+exp(4*eval_expr(p, e->param[0])));
         case e_gauss: { double d = eval_expr(p, e->param[0]); return exp(-d*d/2)/sqrt(2*M_PI); }

         case e_ld:     return e->value * p->var[av_clip(eval_expr(p, e->param[0]), 0, VARS-1)];

         case e_isnan:  return e->value * !!isnan(eval_expr(p, e->param[0]));

         case e_isinf:  return e->value * !!isinf(eval_expr(p, e->param[0]));

         case e_floor:  return e->value * floor(eval_expr(p, e->param[0]));
         case e_ceil :  return e->value * ceil (eval_expr(p, e->param[0]));
         case e_trunc:  return e->value * trunc(eval_expr(p, e->param[0]));

         case e_round:  return e->value * round(eval_expr(p, e->param[0]));

         case e_sqrt:   return e->value * sqrt (eval_expr(p, e->param[0]));

         case e_not:    return e->value * (eval_expr(p, e->param[0]) == 0);

         case e_if:     return e->value * (eval_expr(p, e->param[0]) ? eval_expr(p, e->param[1]) :
                                           e->param[2] ? eval_expr(p, e->param[2]) : 0);
         case e_ifnot:  return e->value * (!eval_expr(p, e->param[0]) ? eval_expr(p, e->param[1]) :
                                           e->param[2] ? eval_expr(p, e->param[2]) : 0);

         case e_clip: {
             double x = eval_expr(p, e->param[0]);
             double min = eval_expr(p, e->param[1]), max = eval_expr(p, e->param[2]);
             if (isnan(min) || isnan(max) || isnan(x) || min > max)
                 return NAN;
             return e->value * av_clipd(eval_expr(p, e->param[0]), min, max);
         }

         case e_between: {
             double d = eval_expr(p, e->param[0]);
             return e->value * (d >= eval_expr(p, e->param[1]) &&
                                d <= eval_expr(p, e->param[2]));
         }

         case e_lerp: {
             double v0 = eval_expr(p, e->param[0]);
             double v1 = eval_expr(p, e->param[1]);
             double f  = eval_expr(p, e->param[2]);
             return v0 + (v1 - v0) * f;
         }

         case e_print: {
             double x = eval_expr(p, e->param[0]);
             int level = e->param[1] ? av_clip(eval_expr(p, e->param[1]), INT_MIN, INT_MAX) : AV_LOG_INFO;
             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));
         }

         case e_while: {

             double d = NAN;

             while (eval_expr(p, e->param[0]))

                 d=eval_expr(p, e->param[1]);
             return d;
         }

         case e_taylor: {
             double t = 1, d = 0, v;
             double x = eval_expr(p, e->param[1]);

             int id = e->param[2] ? av_clip(eval_expr(p, e->param[2]), 0, VARS-1) : 0;

             int i;

             double var0 = p->var[id];

             for(i=0; i<1000; i++) {
                 double ld = d;

                 p->var[id] = i;

                 v = eval_expr(p, e->param[0]);
                 d += t*v;
                 if(ld==d && v)
                     break;
                 t *= x / (i+1);
             }

             p->var[id] = var0;

             return d;
         }

         case e_root: {

             int i, j;

             double low = -1, high = -1, v, low_v = -DBL_MAX, high_v = DBL_MAX;
             double var0 = p->var[0];
             double x_max = eval_expr(p, e->param[1]);
             for(i=-1; i<1024; i++) {
                 if(i<255) {

                     p->var[0] = ff_reverse[i&255]*x_max/255;

                 } else {
                     p->var[0] = x_max*pow(0.9, i-255);
                     if (i&1) p->var[0] *= -1;
                     if (i&2) p->var[0] += low;
                     else     p->var[0] += high;
                 }
                 v = eval_expr(p, e->param[0]);
                 if (v<=0 && v>low_v) {
                     low    = p->var[0];
                     low_v  = v;
                 }
                 if (v>=0 && v<high_v) {
                     high   = p->var[0];
                     high_v = v;
                 }
                 if (low>=0 && high>=0){

                     for (j=0; j<1000; j++) {

                         p->var[0] = (low+high)*0.5;
                         if (low == p->var[0] || high == p->var[0])
                             break;
                         v = eval_expr(p, e->param[0]);
                         if (v<=0) low = p->var[0];
                         if (v>=0) high= p->var[0];
                         if (isnan(v)) {
                             low = high = v;
                             break;
                         }
                     }
                     break;
                 }
             }
             p->var[0] = var0;
             return -low_v<high_v ? low : high;
         }

         default: {
             double d = eval_expr(p, e->param[0]);
             double d2 = eval_expr(p, e->param[1]);
             switch (e->type) {

                 case e_mod: return e->value * (d - floor((!CONFIG_FTRAPV || d2) ? d / d2 : d * INFINITY) * d2);

                 case e_gcd: return e->value * av_gcd(d,d2);

                 case e_max: return e->value * (d >  d2 ?   d : d2);
                 case e_min: return e->value * (d <  d2 ?   d : d2);
                 case e_eq:  return e->value * (d == d2 ? 1.0 : 0.0);
                 case e_gt:  return e->value * (d >  d2 ? 1.0 : 0.0);
                 case e_gte: return e->value * (d >= d2 ? 1.0 : 0.0);

                 case e_lt:  return e->value * (d <  d2 ? 1.0 : 0.0);
                 case e_lte: return e->value * (d <= d2 ? 1.0 : 0.0);

                 case e_pow: return e->value * pow(d, d2);
                 case e_mul: return e->value * (d * d2);

                 case e_div: return e->value * ((!CONFIG_FTRAPV || d2 ) ? (d / d2) : d * INFINITY);

                 case e_add: return e->value * (d + d2);

                 case e_last:return e->value * d2;

                 case e_st : return e->value * (p->var[av_clip(d, 0, VARS-1)]= d2);

                 case e_hypot:return e->value * hypot(d, d2);

                 case e_atan2:return e->value * atan2(d, d2);

                 case e_bitand: return isnan(d) || isnan(d2) ? NAN : e->value * ((long int)d & (long int)d2);
                 case e_bitor:  return isnan(d) || isnan(d2) ? NAN : e->value * ((long int)d | (long int)d2);

             }
         }
     }
     return NAN;
 }
 

 static int parse_expr(AVExpr **e, Parser *p);

 void av_expr_free(AVExpr *e)

 {

     if (!e) return;

     av_expr_free(e->param[0]);
     av_expr_free(e->param[1]);

     av_expr_free(e->param[2]);

     av_freep(&e->var);

     av_freep(&e);
 }
 

 static int parse_primary(AVExpr **e, Parser *p)
 {

     AVExpr *d = av_mallocz(sizeof(AVExpr));

     char *next = p->s, *s0 = p->s;

     int ret, i;

     if (!d)

         return AVERROR(ENOMEM);

     /* number */

     d->value = av_strtod(p->s, &next);

     if (next != p->s) {

         d->type = e_value;

         p->s= next;

         *e = d;
         return 0;

     }

     d->value = 1;

     /* named constants */

     for (i=0; p->const_names && p->const_names[i]; i++) {
         if (strmatch(p->s, p->const_names[i])) {

             p->s+= strlen(p->const_names[i]);

             d->type = e_const;
             d->a.const_index = i;

             *e = d;
             return 0;

         }
     }

     for (i = 0; i < FF_ARRAY_ELEMS(constants); i++) {
         if (strmatch(p->s, constants[i].name)) {
             p->s += strlen(constants[i].name);
             d->type = e_value;
             d->value = constants[i].value;
             *e = d;
             return 0;
         }
     }

     p->s= strchr(p->s, '(');

     if (!p->s) {

         av_log(p, AV_LOG_ERROR, "Undefined constant or missing '(' in '%s'\n", s0);

         p->s= next;

         av_expr_free(d);

         return AVERROR(EINVAL);

     }
     p->s++; // "("

     if (*next == '(') { // special case do-nothing
         av_freep(&d);

         if ((ret = parse_expr(&d, p)) < 0)
             return ret;

         if (p->s[0] != ')') {

             av_log(p, AV_LOG_ERROR, "Missing ')' in '%s'\n", s0);

             av_expr_free(d);

             return AVERROR(EINVAL);

         }
         p->s++; // ")"

         *e = d;
         return 0;
     }
     if ((ret = parse_expr(&(d->param[0]), p)) < 0) {

         av_expr_free(d);

         return ret;

     }

     if (p->s[0]== ',') {

         p->s++; // ","

         parse_expr(&d->param[1], p);

     }

     if (p->s[0]== ',') {
         p->s++; // ","
         parse_expr(&d->param[2], p);
     }

     if (p->s[0] != ')') {

         av_log(p, AV_LOG_ERROR, "Missing ')' or too many args in '%s'\n", s0);

         av_expr_free(d);

         return AVERROR(EINVAL);

     }
     p->s++; // ")"

     d->type = e_func0;

          if (strmatch(next, "sinh"  )) d->a.func0 = sinh;
     else if (strmatch(next, "cosh"  )) d->a.func0 = cosh;
     else if (strmatch(next, "tanh"  )) d->a.func0 = tanh;
     else if (strmatch(next, "sin"   )) d->a.func0 = sin;
     else if (strmatch(next, "cos"   )) d->a.func0 = cos;
     else if (strmatch(next, "tan"   )) d->a.func0 = tan;
     else if (strmatch(next, "atan"  )) d->a.func0 = atan;
     else if (strmatch(next, "asin"  )) d->a.func0 = asin;
     else if (strmatch(next, "acos"  )) d->a.func0 = acos;
     else if (strmatch(next, "exp"   )) d->a.func0 = exp;
     else if (strmatch(next, "log"   )) d->a.func0 = log;
     else if (strmatch(next, "abs"   )) d->a.func0 = fabs;

     else if (strmatch(next, "time"  )) d->a.func0 = etime;

     else if (strmatch(next, "squish")) d->type = e_squish;
     else if (strmatch(next, "gauss" )) d->type = e_gauss;
     else if (strmatch(next, "mod"   )) d->type = e_mod;
     else if (strmatch(next, "max"   )) d->type = e_max;
     else if (strmatch(next, "min"   )) d->type = e_min;
     else if (strmatch(next, "eq"    )) d->type = e_eq;
     else if (strmatch(next, "gte"   )) d->type = e_gte;
     else if (strmatch(next, "gt"    )) d->type = e_gt;

     else if (strmatch(next, "lte"   )) d->type = e_lte;
     else if (strmatch(next, "lt"    )) d->type = e_lt;

     else if (strmatch(next, "ld"    )) d->type = e_ld;

     else if (strmatch(next, "isnan" )) d->type = e_isnan;

     else if (strmatch(next, "isinf" )) d->type = e_isinf;

     else if (strmatch(next, "st"    )) d->type = e_st;
     else if (strmatch(next, "while" )) d->type = e_while;

     else if (strmatch(next, "taylor")) d->type = e_taylor;

     else if (strmatch(next, "root"  )) d->type = e_root;

     else if (strmatch(next, "floor" )) d->type = e_floor;
     else if (strmatch(next, "ceil"  )) d->type = e_ceil;
     else if (strmatch(next, "trunc" )) d->type = e_trunc;

     else if (strmatch(next, "round" )) d->type = e_round;

     else if (strmatch(next, "sqrt"  )) d->type = e_sqrt;

     else if (strmatch(next, "not"   )) d->type = e_not;

     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, "hypot" )) d->type = e_hypot;

     else if (strmatch(next, "gcd"   )) d->type = e_gcd;

     else if (strmatch(next, "if"    )) d->type = e_if;
     else if (strmatch(next, "ifnot" )) d->type = e_ifnot;

     else if (strmatch(next, "bitand")) d->type = e_bitand;
     else if (strmatch(next, "bitor" )) d->type = e_bitor;

     else if (strmatch(next, "between"))d->type = e_between;

     else if (strmatch(next, "clip"  )) d->type = e_clip;

     else if (strmatch(next, "atan2" )) d->type = e_atan2;

     else if (strmatch(next, "lerp"  )) d->type = e_lerp;

     else {

         for (i=0; p->func1_names && p->func1_names[i]; i++) {
             if (strmatch(next, p->func1_names[i])) {

                 d->a.func1 = p->funcs1[i];

                 d->type = e_func1;

                 *e = d;
                 return 0;

             }
         }
 

         for (i=0; p->func2_names && p->func2_names[i]; i++) {
             if (strmatch(next, p->func2_names[i])) {

                 d->a.func2 = p->funcs2[i];

                 d->type = e_func2;

                 *e = d;
                 return 0;

             }
         }
 

         av_log(p, AV_LOG_ERROR, "Unknown function in '%s'\n", s0);

         av_expr_free(d);

         return AVERROR(EINVAL);

     }

     *e = d;
     return 0;

 }

 static AVExpr *make_eval_expr(int type, int value, AVExpr *p0, AVExpr *p1)

 {
     AVExpr *e = av_mallocz(sizeof(AVExpr));

     if (!e)
         return NULL;

     e->type     =type   ;
     e->value    =value  ;
     e->param[0] =p0     ;
     e->param[1] =p1     ;
     return e;
 }
 

 static int parse_pow(AVExpr **e, Parser *p, int *sign)
 {

     *sign= (*p->s == '+') - (*p->s == '-');
     p->s += *sign&1;

     return parse_primary(e, p);

 }
 

 static int parse_dB(AVExpr **e, Parser *p, int *sign)
 {
     /* do not filter out the negative sign when parsing a dB value.
        for example, -3dB is not the same as -(3dB) */
     if (*p->s == '-') {
         char *next;

         double av_unused ignored = strtod(p->s, &next);

         if (next != p->s && next[0] == 'd' && next[1] == 'B') {
             *sign = 0;
             return parse_primary(e, p);
         }
     }
     return parse_pow(e, p, sign);
 }
 

 static int parse_factor(AVExpr **e, Parser *p)
 {
     int sign, sign2, ret;
     AVExpr *e0, *e1, *e2;

     if ((ret = parse_dB(&e0, p, &sign)) < 0)

         return ret;

     while(p->s[0]=='^'){

         e1 = e0;

         p->s++;

         if ((ret = parse_dB(&e2, p, &sign2)) < 0) {

             av_expr_free(e1);

             return ret;
         }

         e0 = make_eval_expr(e_pow, 1, e1, e2);

         if (!e0) {

             av_expr_free(e1);
             av_expr_free(e2);

             return AVERROR(ENOMEM);
         }
         if (e0->param[1]) e0->param[1]->value *= (sign2|1);

     }

     if (e0) e0->value *= (sign|1);
 
     *e = e0;
     return 0;

 }
 

 static int parse_term(AVExpr **e, Parser *p)
 {
     int ret;
     AVExpr *e0, *e1, *e2;
     if ((ret = parse_factor(&e0, p)) < 0)
         return ret;

     while (p->s[0]=='*' || p->s[0]=='/') {

         int c= *p->s++;

         e1 = e0;
         if ((ret = parse_factor(&e2, p)) < 0) {

             av_expr_free(e1);

             return ret;
         }

         e0 = make_eval_expr(c == '*' ? e_mul : e_div, 1, e1, e2);

         if (!e0) {

             av_expr_free(e1);
             av_expr_free(e2);

             return AVERROR(ENOMEM);
         }

     }

     *e = e0;
     return 0;

 }
 

 static int parse_subexpr(AVExpr **e, Parser *p)
 {
     int ret;
     AVExpr *e0, *e1, *e2;
     if ((ret = parse_term(&e0, p)) < 0)
         return ret;

     while (*p->s == '+' || *p->s == '-') {

         e1 = e0;
         if ((ret = parse_term(&e2, p)) < 0) {

             av_expr_free(e1);

             return ret;
         }

         e0 = make_eval_expr(e_add, 1, e1, e2);

         if (!e0) {

             av_expr_free(e1);
             av_expr_free(e2);

             return AVERROR(ENOMEM);
         }

     };
 

     *e = e0;
     return 0;

 }
 

 static int parse_expr(AVExpr **e, Parser *p)
 {
     int ret;
     AVExpr *e0, *e1, *e2;

     if (p->stack_index <= 0) //protect against stack overflows

         return AVERROR(EINVAL);

     p->stack_index--;
 

     if ((ret = parse_subexpr(&e0, p)) < 0)
         return ret;

     while (*p->s == ';') {

         p->s++;

         e1 = e0;
         if ((ret = parse_subexpr(&e2, p)) < 0) {

             av_expr_free(e1);

             return ret;
         }

         e0 = make_eval_expr(e_last, 1, e1, e2);

         if (!e0) {

             av_expr_free(e1);
             av_expr_free(e2);

             return AVERROR(ENOMEM);
         }

     };

 
     p->stack_index++;

     *e = e0;
     return 0;

 }
 

 static int verify_expr(AVExpr *e)
 {

     if (!e) return 0;
     switch (e->type) {
         case e_value:
         case e_const: return 1;
         case e_func0:
         case e_func1:
         case e_squish:

         case e_ld:

         case e_gauss:

         case e_isnan:

         case e_isinf:

         case e_floor:
         case e_ceil:
         case e_trunc:

         case e_round:

         case e_sqrt:

         case e_not:

         case e_random:

             return verify_expr(e->param[0]) && !e->param[1];

         case e_print:
             return verify_expr(e->param[0])
                    && (!e->param[1] || verify_expr(e->param[1]));

         case e_if:
         case e_ifnot:

         case e_taylor:
             return verify_expr(e->param[0]) && verify_expr(e->param[1])
                    && (!e->param[2] || verify_expr(e->param[2]));

         case e_between:

         case e_clip:

         case e_lerp:

             return verify_expr(e->param[0]) &&
                    verify_expr(e->param[1]) &&
                    verify_expr(e->param[2]);

         default: return verify_expr(e->param[0]) && verify_expr(e->param[1]) && !e->param[2];

     }
 }
 

 int av_expr_parse(AVExpr **expr, const char *s,

                   const char * const *const_names,
                   const char * const *func1_names, double (* const *funcs1)(void *, double),
                   const char * const *func2_names, double (* const *funcs2)(void *, double, double),

                   int log_offset, void *log_ctx)

 {

     Parser p = { 0 };

     AVExpr *e = NULL;

     char *w = av_malloc(strlen(s) + 1);
     char *wp = w;

     const char *s0 = s;

     int ret = 0;

 
     if (!w)

         return AVERROR(ENOMEM);

 
     while (*s)

         if (!av_isspace(*s++)) *wp++ = s[-1];

     *wp++ = 0;

     p.class      = &eval_class;

     p.stack_index=100;

     p.s= w;

     p.const_names = const_names;
     p.funcs1      = funcs1;
     p.func1_names = func1_names;
     p.funcs2      = funcs2;
     p.func2_names = func2_names;

     p.log_offset = log_offset;
     p.log_ctx    = log_ctx;

     if ((ret = parse_expr(&e, &p)) < 0)
         goto end;

     if (*p.s) {
         av_log(&p, AV_LOG_ERROR, "Invalid chars '%s' at the end of expression '%s'\n", p.s, s0);
         ret = AVERROR(EINVAL);
         goto end;
     }

     if (!verify_expr(e)) {

         ret = AVERROR(EINVAL);
         goto end;

     }

     e->var= av_mallocz(sizeof(double) *VARS);

     if (!e->var) {
         ret = AVERROR(ENOMEM);
         goto end;
     }

     *expr = e;

     e = NULL;

 end:

     av_expr_free(e);

     av_free(w);

     return ret;

 }
 

 double av_expr_eval(AVExpr *e, const double *const_values, void *opaque)

 {

     Parser p = { 0 };

     p.var= e->var;

     p.const_values = const_values;

     p.opaque     = opaque;
     return eval_expr(&p, e);
 }
 

 int av_expr_parse_and_eval(double *d, const char *s,

                            const char * const *const_names, const double *const_values,
                            const char * const *func1_names, double (* const *funcs1)(void *, double),
                            const char * const *func2_names, double (* const *funcs2)(void *, double, double),

                            void *opaque, int log_offset, void *log_ctx)

 {

     AVExpr *e = NULL;

     int ret = av_expr_parse(&e, s, const_names, func1_names, funcs1, func2_names, funcs2, log_offset, log_ctx);

 
     if (ret < 0) {
         *d = NAN;
         return ret;
     }

     *d = av_expr_eval(e, const_values, opaque);
     av_expr_free(e);

     return isnan(*d) ? AVERROR(EINVAL) : 0;

 }