1 @chapter Expression Evaluation
2 @c man begin EXPRESSION EVALUATION
4 When evaluating an arithemetic 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.
55 Allow to load the value of the internal variable with number
56 @var{var}, which was previosly stored with st(@var{var}, @var{expr}).
57 The function returns the loaded value.
59 @item while(cond, expr)
60 Evaluate expression @var{expr} while the expression @var{cond} is
61 non-zero, and returns the value of the last @var{expr} evaluation, or
62 NAN if @var{cond} was always false.
65 Round the value of expression @var{expr} upwards to the nearest
66 integer. For example, "ceil(1.5)" is "2.0".
69 Round the value of expression @var{expr} downwards to the nearest
70 integer. For example, "floor(-1.5)" is "-2.0".
73 Round the value of expression @var{expr} towards zero to the nearest
74 integer. For example, "trunc(-1.5)" is "-1.0".
77 Compute the square root of @var{expr}. This is equivalent to
81 Return 1.0 if @var{expr} is zero, 0.0 otherwise.
84 Compute the power of @var{x} elevated @var{y}, it is equivalent to
85 "(@var{x})^(@var{y})".
88 Return a pseudo random value between 0.0 and 1.0. @var{x} is the index of the
89 internal variable which will be used to save the seed/state.
92 This function is similar to the C function with the same name; it returns
93 "sqrt(@var{x}*@var{x} + @var{y}*@var{y})", the length of the hypotenuse of a
94 right triangle with sides of length @var{x} and @var{y}, or the distance of the
95 point (@var{x}, @var{y}) from the origin.
98 Return the greatest common divisor of @var{x} and @var{y}. If both @var{x} and
99 @var{y} are 0 or either or both are less than zero then behavior is undefined.
102 The following constants are available:
105 area of the unit disc, approximatively 3.14
107 exp(1) (Euler's number), approximatively 2.718
109 golden ratio (1+sqrt(5))/2, approximatively 1.618
114 @code{*} works like AND
116 @code{+} works like OR
127 In your C code, you can extend the list of unary and binary functions,
128 and define recognized constants, so that they are available for your
131 The evaluator also recognizes the International System number
132 postfixes. If 'i' is appended after the postfix, powers of 2 are used
133 instead of powers of 10. The 'B' postfix multiplies the value for 8,
134 and can be appended after another postfix or used alone. This allows
135 using for example 'KB', 'MiB', 'G' and 'B' as postfix.
137 Follows the list of available International System postfixes, with
138 indication of the corresponding powers of 10 and of 2.