mirror of
https://git.videolan.org/git/ffmpeg.git
synced 2024-09-08 16:56:57 +02:00
157 lines
3.4 KiB
Plaintext
157 lines
3.4 KiB
Plaintext
@chapter Expression Evaluation
|
|
@c man begin EXPRESSION EVALUATION
|
|
|
|
When evaluating an arithmetic expression, Libav uses an internal
|
|
formula evaluator, implemented through the @file{libavutil/eval.h}
|
|
interface.
|
|
|
|
An expression may contain unary, binary operators, constants, and
|
|
functions.
|
|
|
|
Two expressions @var{expr1} and @var{expr2} can be combined to form
|
|
another expression "@var{expr1};@var{expr2}".
|
|
@var{expr1} and @var{expr2} are evaluated in turn, and the new
|
|
expression evaluates to the value of @var{expr2}.
|
|
|
|
The following binary operators are available: @code{+}, @code{-},
|
|
@code{*}, @code{/}, @code{^}.
|
|
|
|
The following unary operators are available: @code{+}, @code{-}.
|
|
|
|
The following functions are available:
|
|
@table @option
|
|
@item sinh(x)
|
|
@item cosh(x)
|
|
@item tanh(x)
|
|
@item sin(x)
|
|
@item cos(x)
|
|
@item tan(x)
|
|
@item atan(x)
|
|
@item asin(x)
|
|
@item acos(x)
|
|
@item exp(x)
|
|
@item log(x)
|
|
@item abs(x)
|
|
@item squish(x)
|
|
@item gauss(x)
|
|
@item isinf(x)
|
|
Return 1.0 if @var{x} is +/-INFINITY, 0.0 otherwise.
|
|
@item isnan(x)
|
|
Return 1.0 if @var{x} is NAN, 0.0 otherwise.
|
|
|
|
@item mod(x, y)
|
|
@item max(x, y)
|
|
@item min(x, y)
|
|
@item eq(x, y)
|
|
@item gte(x, y)
|
|
@item gt(x, y)
|
|
@item lte(x, y)
|
|
@item lt(x, y)
|
|
@item st(var, expr)
|
|
Allow to store the value of the expression @var{expr} in an internal
|
|
variable. @var{var} specifies the number of the variable where to
|
|
store the value, and it is a value ranging from 0 to 9. The function
|
|
returns the value stored in the internal variable.
|
|
|
|
@item ld(var)
|
|
Allow to load the value of the internal variable with number
|
|
@var{var}, which was previously stored with st(@var{var}, @var{expr}).
|
|
The function returns the loaded value.
|
|
|
|
@item while(cond, expr)
|
|
Evaluate expression @var{expr} while the expression @var{cond} is
|
|
non-zero, and returns the value of the last @var{expr} evaluation, or
|
|
NAN if @var{cond} was always false.
|
|
|
|
@item ceil(expr)
|
|
Round the value of expression @var{expr} upwards to the nearest
|
|
integer. For example, "ceil(1.5)" is "2.0".
|
|
|
|
@item floor(expr)
|
|
Round the value of expression @var{expr} downwards to the nearest
|
|
integer. For example, "floor(-1.5)" is "-2.0".
|
|
|
|
@item trunc(expr)
|
|
Round the value of expression @var{expr} towards zero to the nearest
|
|
integer. For example, "trunc(-1.5)" is "-1.0".
|
|
|
|
@item sqrt(expr)
|
|
Compute the square root of @var{expr}. This is equivalent to
|
|
"(@var{expr})^.5".
|
|
|
|
@item not(expr)
|
|
Return 1.0 if @var{expr} is zero, 0.0 otherwise.
|
|
@end table
|
|
|
|
Note that:
|
|
|
|
@code{*} works like AND
|
|
|
|
@code{+} works like OR
|
|
|
|
thus
|
|
@example
|
|
if A then B else C
|
|
@end example
|
|
is equivalent to
|
|
@example
|
|
A*B + not(A)*C
|
|
@end example
|
|
|
|
In your C code, you can extend the list of unary and binary functions,
|
|
and define recognized constants, so that they are available for your
|
|
expressions.
|
|
|
|
The evaluator also recognizes the International System number
|
|
postfixes. If 'i' is appended after the postfix, powers of 2 are used
|
|
instead of powers of 10. The 'B' postfix multiplies the value for 8,
|
|
and can be appended after another postfix or used alone. This allows
|
|
using for example 'KB', 'MiB', 'G' and 'B' as postfix.
|
|
|
|
Follows the list of available International System postfixes, with
|
|
indication of the corresponding powers of 10 and of 2.
|
|
@table @option
|
|
@item y
|
|
-24 / -80
|
|
@item z
|
|
-21 / -70
|
|
@item a
|
|
-18 / -60
|
|
@item f
|
|
-15 / -50
|
|
@item p
|
|
-12 / -40
|
|
@item n
|
|
-9 / -30
|
|
@item u
|
|
-6 / -20
|
|
@item m
|
|
-3 / -10
|
|
@item c
|
|
-2
|
|
@item d
|
|
-1
|
|
@item h
|
|
2
|
|
@item k
|
|
3 / 10
|
|
@item K
|
|
3 / 10
|
|
@item M
|
|
6 / 20
|
|
@item G
|
|
9 / 30
|
|
@item T
|
|
12 / 40
|
|
@item P
|
|
15 / 40
|
|
@item E
|
|
18 / 50
|
|
@item Z
|
|
21 / 60
|
|
@item Y
|
|
24 / 70
|
|
@end table
|
|
|
|
@c man end
|