1 @chapter Expression Evaluation
2 @c man begin EXPRESSION EVALUATION
4 When evaluating an arithmetic expression, FFmpeg uses an internal
5 formula evaluator, implemented through the @file{libavutil/eval.h}
8 An expression may contain unary, binary operators, constants, and
11 Two expressions @var{expr1} and @var{expr2} can be combined to form
12 another expression "@var{expr1};@var{expr2}".
13 @var{expr1} and @var{expr2} are evaluated in turn, and the new
14 expression evaluates to the value of @var{expr2}.
16 The following binary operators are available: @code{+}, @code{-},
17 @code{*}, @code{/}, @code{^}.
19 The following unary operators are available: @code{+}, @code{-}.
21 The following functions are available:
38 Return 1.0 if @var{x} is NAN, 0.0 otherwise.
49 Allow to store the value of the expression @var{expr} in an internal
50 variable. @var{var} specifies the number of the variable where to
51 store the value, and it is a value ranging from 0 to 9. The function
52 returns the value stored in the internal variable.
53 Note, Variables are currently not shared between expressions.
56 Allow to load the value of the internal variable with number
57 @var{var}, which was previously stored with st(@var{var}, @var{expr}).
58 The function returns the loaded value.
60 @item while(cond, expr)
61 Evaluate expression @var{expr} while the expression @var{cond} is
62 non-zero, and returns the value of the last @var{expr} evaluation, or
63 NAN if @var{cond} was always false.
66 Round the value of expression @var{expr} upwards to the nearest
67 integer. For example, "ceil(1.5)" is "2.0".
70 Round the value of expression @var{expr} downwards to the nearest
71 integer. For example, "floor(-1.5)" is "-2.0".
74 Round the value of expression @var{expr} towards zero to the nearest
75 integer. For example, "trunc(-1.5)" is "-1.0".
78 Compute the square root of @var{expr}. This is equivalent to
82 Return 1.0 if @var{expr} is zero, 0.0 otherwise.
85 Compute the power of @var{x} elevated @var{y}, it is equivalent to
86 "(@var{x})^(@var{y})".
89 Return a pseudo random value between 0.0 and 1.0. @var{x} is the index of the
90 internal variable which will be used to save the seed/state.
93 This function is similar to the C function with the same name; it returns
94 "sqrt(@var{x}*@var{x} + @var{y}*@var{y})", the length of the hypotenuse of a
95 right triangle with sides of length @var{x} and @var{y}, or the distance of the
96 point (@var{x}, @var{y}) from the origin.
99 Return the greatest common divisor of @var{x} and @var{y}. If both @var{x} and
100 @var{y} are 0 or either or both are less than zero then behavior is undefined.
103 Evaluate @var{x}, and if the result is non-zero return the result of
104 the evaluation of @var{y}, return 0 otherwise.
107 Evaluate @var{x}, and if the result is zero return the result of the
108 evaluation of @var{y}, return 0 otherwise.
110 @item taylor(expr, x) taylor(expr, x, id)
111 Evaluate a taylor series at x.
112 expr represents the LD(id)-th derivates of f(x) at 0. If id is not specified
114 note, when you have the derivatives at y instead of 0
115 taylor(expr, x-y) can be used
116 When the series does not converge the results are undefined.
118 @item root(expr, max)
119 Finds x where f(x)=0 in the interval 0..max.
120 f() must be continuous or the result is undefined.
123 The following constants are available:
126 area of the unit disc, approximately 3.14
128 exp(1) (Euler's number), approximately 2.718
130 golden ratio (1+sqrt(5))/2, approximately 1.618
133 Assuming that an expression is considered "true" if it has a non-zero
136 @code{*} works like AND
138 @code{+} works like OR
149 In your C code, you can extend the list of unary and binary functions,
150 and define recognized constants, so that they are available for your
153 The evaluator also recognizes the International System number
154 postfixes. If 'i' is appended after the postfix, powers of 2 are used
155 instead of powers of 10. The 'B' postfix multiplies the value for 8,
156 and can be appended after another postfix or used alone. This allows
157 using for example 'KB', 'MiB', 'G' and 'B' as postfix.
159 Follows the list of available International System postfixes, with
160 indication of the corresponding powers of 10 and of 2.