Table of Contents
This function will evaluate a mathematical expression that may contain variables and format the result according to the provided formatt string.
The formatting string uses the standard POSIX printf format.
All the mathematical computations are done using floats.
The supported infix mathematical syntax, in order of precedence, is:
-
(and)parentheses for grouping expressions -
^operator for exponentiation -
*and/operators for multiplication and division -
%operators for modulo operation -
+and-operators for addition and subtraction -
=="close enough" operator to tell if two expressions evaluate to the same number, with a tiny margin to tolerate floating point errors. It returns 1 or 0. -
>="greater or close enough" operator with a tiny margin to tolerate floating point errors. It returns 1 or 0. -
>"greater than" operator. It returns 1 or 0. -
<="less than or close enough" operator with a tiny margin to tolerate floating point errors. It returns 1 or 0. -
<"less than" operator. It returns 1 or 0.
The numbers can be in any format acceptable to the C scanf function
with the %lf format specifier, followed by the k, m, g, t, or
p SI units. So e.g. -100 and 2.34m are valid numbers.
In addition, the following constants are recognized:
-
e: 2.7182818284590452354 -
log2e: 1.4426950408889634074 -
log10e: 0.43429448190325182765 -
ln2: 0.69314718055994530942 -
ln10: 2.30258509299404568402 -
pi: 3.14159265358979323846 -
pi_2: 1.57079632679489661923 (pi over 2) -
pi_4: 0.78539816339744830962 (pi over 4) -
1_pi: 0.31830988618379067154 (1 over pi) -
2_pi: 0.63661977236758134308 (2 over pi) -
2_sqrtpi: 1.12837916709551257390 (2 over square root of pi) -
sqrt2: 1.41421356237309504880 (square root of 2) -
sqrt1_2: 0.70710678118654752440 (square root of 1/2)
The following functions can be used, with parentheses:
-
ceilandfloor: the next highest or the previous highest integer -
log10,log2,log -
sqrt -
sin,cos,tan,asin,acos,atan -
abs: absolute value -
step: 0 if the argument is negative, 1 otherwise
The format field supports the following specifiers:
-
%dfor decimal integer -
%xfor hexadecimal integer -
%ofor octal integer -
%ffor decimal floating point
You can use usual flags, width and precision syntax.
If you use:
variable_string("prefix", "var", "10");
variable_string_from_math_expression("prefix", "sum", "2.0+3.0", "%d");
variable_string_from_math_expression("prefix", "product", "3*${prefix.var}", "%d");
The prefix.sum string variable will contain 5 and prefix.product
will contain 30.
- variable_prefix: The prefix of the variable name
- variable_name: The variable to define, the full name will be variable_prefix.variable_name
- expression: The mathematical expression to evaluate
- format: The format string to use
variable_string_from_math_expression_${variable_name}_{kept, repaired, not_ok, reached}
