SET (/A) Command (floating point)

The SET /A command enables the value of an arithmetical expression to be stored into a variable.

This manual pages is only about the use of the /A of the SET command. To learn more about the general use of the command, please see the SET manual page.

Synopsis

SET [/a] variable=expression

Computes the value of the arithmetical expression expression and stores it into variable. Unlike the original batch command of cmd, the SET command also provide support for floating point numbers, if floating-point values are given inside the expression. This behaviour is explained in detail in the Toogling floating-point expression section.

The = sign can be prefixed with one the of the supported binary operator, in which case, SET /a stores the result of variable binary_operator (expression) inside variable. For instance:

:: equivalent to SET /a var=var+3
SET /a var+=3

The given expression must consist of a sequence of operands separated by operators.

Operands

Operands represent the numbers to which a sequence of operations will be applies. Operands must be of one the following types:

• A number litteral, that is a string representing a number. Number can be specified using one of the following syntaxes:

  • As floating point value, if the number conforms to the following format : [+|-]d.ddddd[E[+|-]nnn]. If any floating point value are specified, then the evaluating mode switches to floating-point mode and divisions are handled as floating point division.

  • As integer values. Three different numeric bases are available: decimal, octal and hexadecimal. By default, numbers are suposed to be decimal, unless it is prefixed by one of the following prefix:

    • 0x : Hexadecimal number.

    • 0 : Octal number.

• A function call, that is a function name followed by a expression :

    function_name(expression)
  

  A list of functions provided by the SET command is provided in the Functions subsection. Note that using functions also toogles the use of floating-point mode.

• A mathematical constant name. A list of constant names are provided in the constant section. Note that using constants also trigger the use of floating-point mode.

• Special numbers, that are values that are not techniacally numbers but are encountered when an illegal operation (dividing by 0 for example) is performed, or when a operation overflows the capacity of the integer.

• inf (INFINITY) : Infinite value.

• nan (NotANumber) : not a number.

• If the operand does not meet any of the preceeding rules, then the operand is considered to be a variable name which will be expanded to the variable value when computing the expression result.

Operators

The SET /a provides a wide variety of operators that can be used with both integers and floating point numbers.

The topmost precedence is given to the 3 following unary operators (an unary operator is an operator that only takes one operand to the right):

• - : Minus sign.

• ! : Logical negation. Note this operation is usually only applied to integer numbers. If the expression toogles the use of floating-point numbers, then the value of the operand is converted to integer (that is, the value is truncated toward 0), then the logical negation is applied and the result is converted back to floating-point number.

• ~ : Bitwise negation. The same remark as above also applies to this operator.

Then, the following binary operators are processed (a binary operator is an operator that takes two operands):

• * : Multiplication.

• / : Division. Note that if floating-point is not toogled by expression (see below), the result of the division is rounded towards 0 (if the result overflows the behaviours is not defined).

• % : Modulo.

• + : Addition.

• - : Subtraction.

  • » : Right shift. As for the ! operator, this operation is usually only applied to integers. Thus if floating point numbers are used, both operands are rounded towards 0, the operation is performed and the result is converted back.

  • « : Left shift. Same remark as above apply.

  • & : Bitwise and. Same remark as above apply.

  • ^ : Bitwise xor. Same remark as above apply.

  • | : Bitwise or. Same remark as above apply.

  • && : Logical and. Same remark as above apply.

  • || : Logical or. Same remark as above apply.

• = : Assignment.

Operators have the following precedence (from greatest to lowest):

• unary operators

• ^

• =

• *, /, %

• +, -

• «, »

• &

• ^

• |

• &&

• ||

To avoid precedence issues, use the parenthesis ( and ).

Functions

Available functions are:

• exp : Exponential.

• log : Neperian logarithm.

• log10 : Decimal logarithm.

• sqrt : Square root.

• Trigonometry :

  • sin : Sine.

  • cos : Cosine.

  • tan : Tangent.

  • cot : Cotangent.

  • sec : Secant.

  • csc : Cosecant.

• Reverse Trigonometry :

  • asin : Reverse sine.

  • acos : Reverse cosine.

  • atan : Reverse tangent.

  • acot : Reverse cotangent.

  • acec : Reverse secant.

  • acsc : Reverse cosecant.

• Hyperbolic trigonometry :

  • sinh : Hyperbolic sine.

  • cosh : Hyperbolic cosine.

  • tanh : Hyperbolic tangent.

  • coth : Hyperbolic cotangent.

  • sech : Hyperbolic secant.

  • csch : Hyperbolic cosecant.

• Reverse hyperbolic trigonometry :

  • asinh : Reverse hyperbolic sine.

  • acosh : Reverse hyperbolic cosine.

  • atanh : Reverse hyperbolic tangent.

  • acoth : Reverse hyperbolic cotangent.

  • acech : Reverse hyperbolic secant.

  • acsch : Reverse hyperbolic cosecant.

• abs : Absolute value.

• step : Step function (Heaviside’s function). Returns 0 if x < 0, 1 else.

• delta : Dirac’s function. Returns plus infinity if x = 0 and 0 else.

• nandelta : Dirac’s function returning NAN instead of infinity.

Constants

Finally, the following constants are defined

• e

• log2e : log2(e)

• log10e : log10(e)

• ln2 : ln(2)

• ln10 : ln(10)

• pi

• pi_2 : pi/2

• pi_4 : pi/4

• 1_pi : 1/pi

• 2_pi : 2/pi

• 2_sqrtpi : 2/sqrt(pi)

• sqrt2 : sqrt(2)

• sqrt1_2 : sqrt(1/2), or 1/sqrt(2) or sqrt(2)/2.

Toogling floating-point expressions

The use of floating-point arithmetics is triggered by the use of one of the following features :

• Specifying a number as a floating-point value

• Using one of the provided functions

• Using one of the provided constants

If none of these conditions are met and the use of floating point is required, one can force it using an operation that does not change the result but use floats (for example adding 0.0) as in the following sample:

:: By default this use integers arithmetics
SET /a var=a/b
:: Trigger the use of floating point arithmetics
SET /a var=a/b+0.0

Precisness

Integers wich are usually bound between -2 147 483 648 and +2 147 483 647.

Floating-point numbers offer a much greater range, between 2,2250738585072014e-308 à 1,7976931348623157e+308. However, this gain on range causes a loss of precision because of approached computing.

Bugs

It is possible to encounter preciseness bug as floating-point number have a finite precision of about 15 decimal places. As a result some expression may be subject to approximation errors when dealing with numbers several orders of magnitude away from one another. Here is an example:

(2e60+1)-2e60)

Computing this expression using floating points arithmetics will lead to a precision error as the result would be 0 even though it is clearly 1. This happen because 10^60 is several orders of magnitude greater than 1. Changing slightly the expression can fix this issue :

2e60-2e60+1

Notes

This command uses a modified version of the GNU libmatheval library.

Compatibility

Available since 0.7.1.0, before the support of expressions was incomplete, supporting neither the % operating system nor functions.

Not compatible with cmd.exe that does not support floating point arithmetics.

See also

SET Command, SET (/a) Command (integers)