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 Stefano Sabatini committed Nov 03, 2010 1 2 3 ``````@chapter Expression Evaluation @c man begin EXPRESSION EVALUATION `````` Diego Biurrun committed Dec 11, 2011 4 ``````When evaluating an arithmetic expression, Libav uses an internal `````` Stefano Sabatini committed Nov 03, 2010 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 ``````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) `````` Martin Storsjö committed Jul 04, 2012 37 38 ``````@item isinf(x) Return 1.0 if @var{x} is +/-INFINITY, 0.0 otherwise. `````` Stefano Sabatini committed Nov 03, 2010 39 40 41 ``````@item isnan(x) Return 1.0 if @var{x} is NAN, 0.0 otherwise. `````` Stefano Sabatini committed Nov 03, 2010 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 ``````@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 `````` Diego Biurrun committed Dec 11, 2011 58 ``````@var{var}, which was previously stored with st(@var{var}, @var{expr}). `````` Stefano Sabatini committed Nov 03, 2010 59 60 61 62 63 64 ``````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. `````` Stefano Sabatini committed Apr 10, 2011 65 66 67 68 69 70 71 72 73 74 75 76 `````` @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". `````` Stefano Sabatini committed Sep 19, 2011 77 78 79 80 `````` @item sqrt(expr) Compute the square root of @var{expr}. This is equivalent to "(@var{expr})^.5". `````` Stefano Sabatini committed Sep 19, 2011 81 82 83 `````` @item not(expr) Return 1.0 if @var{expr} is zero, 0.0 otherwise. `````` Stefano Sabatini committed Nov 03, 2010 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 ``````@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``````