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1c23abc88f
1)Some filters allow cross-referenced expressions e.g. x=y+10. In such cases, filters evaluate expressions multiple times for successful evaluation of all expressions. If the expression for one or more variables contains a RNG, the result may vary across evaluation leading to inconsistent values across the cross-referenced expressions. 2)A related case is circular expressions e.g. x=y+10 and y=x+10 which cannot be succesfully resolved. 3)Certain filter variables may only be applicable in specific eval modes and lead to a failure of evaluation in other modes e.g. pts is only relevant for frame eval mode. At present, there is no reliable means to identify these occurrences and thus the error messages provided are broad or inaccurate. The helper function introduced - av_expr_count_vars - allows developers to identify the use and count of variables in expressions and thus tailor the error message, allow for a graceful fallback and/or decide evaluation order.
124 lines
5.6 KiB
C
124 lines
5.6 KiB
C
/*
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* Copyright (c) 2002 Michael Niedermayer <michaelni@gmx.at>
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*
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* This file is part of FFmpeg.
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*
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* FFmpeg is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* FFmpeg is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with FFmpeg; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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/**
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* @file
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* simple arithmetic expression evaluator
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*/
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#ifndef AVUTIL_EVAL_H
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#define AVUTIL_EVAL_H
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#include "avutil.h"
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typedef struct AVExpr AVExpr;
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/**
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* Parse and evaluate an expression.
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* Note, this is significantly slower than av_expr_eval().
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*
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* @param res a pointer to a double where is put the result value of
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* the expression, or NAN in case of error
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* @param s expression as a zero terminated string, for example "1+2^3+5*5+sin(2/3)"
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* @param const_names NULL terminated array of zero terminated strings of constant identifiers, for example {"PI", "E", 0}
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* @param const_values a zero terminated array of values for the identifiers from const_names
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* @param func1_names NULL terminated array of zero terminated strings of funcs1 identifiers
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* @param funcs1 NULL terminated array of function pointers for functions which take 1 argument
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* @param func2_names NULL terminated array of zero terminated strings of funcs2 identifiers
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* @param funcs2 NULL terminated array of function pointers for functions which take 2 arguments
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* @param opaque a pointer which will be passed to all functions from funcs1 and funcs2
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* @param log_ctx parent logging context
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* @return >= 0 in case of success, a negative value corresponding to an
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* AVERROR code otherwise
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*/
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int av_expr_parse_and_eval(double *res, const char *s,
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const char * const *const_names, const double *const_values,
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const char * const *func1_names, double (* const *funcs1)(void *, double),
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const char * const *func2_names, double (* const *funcs2)(void *, double, double),
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void *opaque, int log_offset, void *log_ctx);
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/**
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* Parse an expression.
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*
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* @param expr a pointer where is put an AVExpr containing the parsed
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* value in case of successful parsing, or NULL otherwise.
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* The pointed to AVExpr must be freed with av_expr_free() by the user
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* when it is not needed anymore.
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* @param s expression as a zero terminated string, for example "1+2^3+5*5+sin(2/3)"
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* @param const_names NULL terminated array of zero terminated strings of constant identifiers, for example {"PI", "E", 0}
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* @param func1_names NULL terminated array of zero terminated strings of funcs1 identifiers
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* @param funcs1 NULL terminated array of function pointers for functions which take 1 argument
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* @param func2_names NULL terminated array of zero terminated strings of funcs2 identifiers
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* @param funcs2 NULL terminated array of function pointers for functions which take 2 arguments
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* @param log_ctx parent logging context
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* @return >= 0 in case of success, a negative value corresponding to an
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* AVERROR code otherwise
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*/
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int av_expr_parse(AVExpr **expr, const char *s,
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const char * const *const_names,
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const char * const *func1_names, double (* const *funcs1)(void *, double),
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const char * const *func2_names, double (* const *funcs2)(void *, double, double),
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int log_offset, void *log_ctx);
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/**
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* Evaluate a previously parsed expression.
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*
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* @param const_values a zero terminated array of values for the identifiers from av_expr_parse() const_names
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* @param opaque a pointer which will be passed to all functions from funcs1 and funcs2
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* @return the value of the expression
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*/
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double av_expr_eval(AVExpr *e, const double *const_values, void *opaque);
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/**
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* Track the presence of variables and their number of occurrences in a parsed expression
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*
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* @param counter a zero-initialized array where the count of each variable will be stored
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* @param size size of array
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* @return 0 on success, a negative value indicates that no expression or array was passed
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* or size was zero
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*/
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int av_expr_count_vars(AVExpr *e, unsigned *counter, int size);
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/**
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* Free a parsed expression previously created with av_expr_parse().
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*/
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void av_expr_free(AVExpr *e);
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/**
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* Parse the string in numstr and return its value as a double. If
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* the string is empty, contains only whitespaces, or does not contain
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* an initial substring that has the expected syntax for a
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* floating-point number, no conversion is performed. In this case,
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* returns a value of zero and the value returned in tail is the value
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* of numstr.
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*
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* @param numstr a string representing a number, may contain one of
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* the International System number postfixes, for example 'K', 'M',
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* 'G'. If 'i' is appended after the postfix, powers of 2 are used
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* instead of powers of 10. The 'B' postfix multiplies the value by
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* 8, and can be appended after another postfix or used alone. This
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* allows using for example 'KB', 'MiB', 'G' and 'B' as postfix.
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* @param tail if non-NULL puts here the pointer to the char next
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* after the last parsed character
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*/
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double av_strtod(const char *numstr, char **tail);
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#endif /* AVUTIL_EVAL_H */
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